SQLite

    if( rc==SQLITE_OK ){
      rc = sqlite3Fts5ConfigSetValue(pTab->pConfig, z, pVal, &bError);
    }
    if( rc==SQLITE_OK ){
      if( bError ){
        rc = SQLITE_ERROR;
      }else{
        rc = sqlite3Fts5StorageConfigValue(pTab->pStorage, z, pVal);
      }
    }
  }
  return rc;
}

static int fts5SpecialDelete(

  int iCookie;                    /* Incremented when %_config is modified */
  int pgsz;                       /* Approximate page size used in %_data */
  int nAutomerge;                 /* 'automerge' setting */
  int nCrisisMerge;               /* Maximum allowed segments per level */
  char *zRank;                    /* Name of rank function */
  char *zRankArgs;                /* Arguments to rank function */
};




#define FTS5_CONTENT_NORMAL   0
#define FTS5_CONTENT_NONE     1
#define FTS5_CONTENT_EXTERNAL 2




int sqlite3Fts5ConfigParse(
    Fts5Global*, sqlite3*, int, const char **, Fts5Config**, char**
);
void sqlite3Fts5ConfigFree(Fts5Config*);

void sqlite3Fts5HashFree(Fts5Hash*);

int sqlite3Fts5HashWrite(
  Fts5Hash*,
  i64 iRowid,                     /* Rowid for this entry */
  int iCol,                       /* Column token appears in (-ve -> delete) */
  int iPos,                       /* Position of token within column */

  const char *pToken, int nToken  /* Token to add or remove to or from index */
);

/*
** Empty (but do not delete) a hash table.
*/
void sqlite3Fts5HashClear(Fts5Hash*);

int sqlite3Fts5StorageDocsize(Fts5Storage *p, i64 iRowid, int *aCol);
int sqlite3Fts5StorageSize(Fts5Storage *p, int iCol, i64 *pnAvg);
int sqlite3Fts5StorageRowCount(Fts5Storage *p, i64 *pnRow);

int sqlite3Fts5StorageSync(Fts5Storage *p, int bCommit);
int sqlite3Fts5StorageRollback(Fts5Storage *p);

int sqlite3Fts5StorageConfigValue(Fts5Storage *p, const char*, sqlite3_value*);



int sqlite3Fts5StorageSpecialDelete(Fts5Storage *p, i64 iDel, sqlite3_value**);

int sqlite3Fts5StorageDeleteAll(Fts5Storage *p);
int sqlite3Fts5StorageRebuild(Fts5Storage *p);
int sqlite3Fts5StorageOptimize(Fts5Storage *p);
int sqlite3Fts5StorageMerge(Fts5Storage *p, int nMerge);

  assert( 0==fts5_iswhitespace(z[0]) );
  quote = z[0];
  if( quote=='[' || quote=='\'' || quote=='"' || quote=='`' ){
    fts5Dequote(z);
  }
}

/*
** Argument z points to a nul-terminated string containing an SQL identifier.
** This function returns a copy of the identifier enclosed in backtick 
** quotes.
*/
static char *fts5EscapeName(int *pRc, const char *z){
  char *pRet = 0;
  if( *pRc==SQLITE_OK ){
    int n = strlen(z);
    pRet = (char*)sqlite3_malloc(2 + 2*n + 1);
    if( pRet==0 ){
      *pRc = SQLITE_NOMEM;
    }else{
      int i;
      char *p = pRet;
      *p++ = '`';
      for(i=0; i<n; i++){
        if( z[i]=='`' ) *p++ = '`';
        *p++ = z[i];
      }
      *p++ = '`';
      *p++ = '\0';
    }
  }
  return pRet;
}

/*
** Parse the "special" CREATE VIRTUAL TABLE directive and update
** configuration object pConfig as appropriate.
**
** If successful, object pConfig is updated and SQLITE_OK returned. If
** an error occurs, an SQLite error code is returned and an error message
** may be left in *pzErr. It is the responsibility of the caller to

/*
** Populate the Fts5Config.zContentExprlist string.
*/
static int fts5ConfigMakeExprlist(Fts5Config *p){
  int i;
  int rc = SQLITE_OK;
  Fts5Buffer buf = {0, 0, 0};
  const char *zSep = "";

  sqlite3Fts5BufferAppendPrintf(&rc, &buf, "T.%Q", p->zContentRowid);
  if( p->eContent!=FTS5_CONTENT_NONE ){
    for(i=0; i<p->nCol; i++){
      if( p->eContent==FTS5_CONTENT_EXTERNAL ){
        sqlite3Fts5BufferAppendPrintf(&rc, &buf, ", T.%Q", p->azCol[i]);
      }else{

** Load the contents of the %_config table into memory.
*/
int sqlite3Fts5ConfigLoad(Fts5Config *pConfig, int iCookie){
  const char *zSelect = "SELECT k, v FROM %Q.'%q_config'";
  char *zSql;
  sqlite3_stmt *p = 0;
  int rc;


  /* Set default values */
  pConfig->pgsz = FTS5_DEFAULT_PAGE_SIZE;
  pConfig->nAutomerge = FTS5_DEFAULT_AUTOMERGE;
  pConfig->nCrisisMerge = FTS5_DEFAULT_CRISISMERGE;

  zSql = sqlite3_mprintf(zSelect, pConfig->zDb, pConfig->zName);
  if( zSql==0 ){
    rc = SQLITE_NOMEM;
  }else{
    rc = sqlite3_prepare_v2(pConfig->db, zSql, -1, &p, 0);
    sqlite3_free(zSql);
  }

  assert( rc==SQLITE_OK || p==0 );
  if( rc==SQLITE_OK ){
    while( SQLITE_ROW==sqlite3_step(p) ){
      const char *zK = (const char*)sqlite3_column_text(p, 0);
      sqlite3_value *pVal = sqlite3_column_value(p, 1);



      sqlite3Fts5ConfigSetValue(pConfig, zK, pVal, 0);
    }

    rc = sqlite3_finalize(p);




  }

  if( rc==SQLITE_OK ){
    pConfig->iCookie = iCookie;
  }
  return rc;
}

#endif /* SQLITE_ENABLE_FTS5 */

static char *fts5PrintfAppend(char *zApp, const char *zFmt, ...){
  char *zNew;
  va_list ap;
  va_start(ap, zFmt);
  zNew = sqlite3_vmprintf(zFmt, ap);
  va_end(ap);
  if( zApp ){
    char *zNew2 = sqlite3_mprintf("%s%s", zApp, zNew);
    sqlite3_free(zNew);
    zNew = zNew2;
  }
  sqlite3_free(zApp);
  return zNew;
}

  int rc;
  int i;

  const char **azConfig;          /* Array of arguments for Fts5Config */
  const char *zNearsetCmd = "nearset";
  int nConfig;                    /* Size of azConfig[] */
  Fts5Config *pConfig = 0;


  if( bTcl && nArg>1 ){
    zNearsetCmd = (const char*)sqlite3_value_text(apVal[1]);

  }

  nConfig = nArg + 2 - bTcl;
  azConfig = (const char**)sqlite3_malloc(sizeof(char*) * nConfig);
  if( azConfig==0 ){
    sqlite3_result_error_nomem(pCtx);
    return;
  }
  azConfig[0] = 0;
  azConfig[1] = "main";
  azConfig[2] = "tbl";
  for(i=1+bTcl; i<nArg; i++){
    azConfig[i+2-bTcl] = (const char*)sqlite3_value_text(apVal[i]);
  }

  zExpr = (const char*)sqlite3_value_text(apVal[0]);

  rc = sqlite3Fts5ConfigParse(pGlobal, db, nConfig, azConfig, &pConfig, &zErr);
  if( rc==SQLITE_OK ){
    rc = sqlite3Fts5ExprNew(pConfig, zExpr, &pExpr, &zErr);
  }
  if( rc==SQLITE_OK ){
    char *zText;
    if( pExpr->pRoot==0 ){
      zText = sqlite3_mprintf("");
    }else if( bTcl ){
      zText = fts5ExprPrintTcl(pConfig, zNearsetCmd, pExpr->pRoot);
    }else{
      zText = fts5ExprPrint(pConfig, pExpr->pRoot);
    }

    if( rc==SQLITE_OK ){

      sqlite3_result_text(pCtx, zText, -1, SQLITE_TRANSIENT);
      sqlite3_free(zText);
    }
  }

  if( rc!=SQLITE_OK ){
    if( zErr ){

  int i;
  unsigned int h = 13;
  for(i=n-1; i>=0; i--){
    h = (h << 3) ^ h ^ p[i];
  }
  return (h % nSlot);
}











/*
** Resize the hash table by doubling the number of slots.
*/
static int fts5HashResize(Fts5Hash *pHash){
  int nNew = pHash->nSlot*2;
  int i;

}

int sqlite3Fts5HashWrite(
  Fts5Hash *pHash,
  i64 iRowid,                     /* Rowid for this entry */
  int iCol,                       /* Column token appears in (-ve -> delete) */
  int iPos,                       /* Position of token within column */

  const char *pToken, int nToken  /* Token to add or remove to or from index */
){
  unsigned int iHash = fts5HashKey(pHash->nSlot, pToken, nToken);
  Fts5HashEntry *p;
  u8 *pPtr;
  int nIncr = 0;                  /* Amount to increment (*pHash->pnByte) by */

  /* Attempt to locate an existing hash entry */
  for(p=pHash->aSlot[iHash]; p; p=p->pHashNext){


    if( memcmp(p->zKey, pToken, nToken)==0 && p->zKey[nToken]==0 ) break;



  }

  /* If an existing hash entry cannot be found, create a new one. */
  if( p==0 ){
    int nByte = sizeof(Fts5HashEntry) + nToken + 1 + 64;
    if( nByte<128 ) nByte = 128;

    if( (pHash->nEntry*2)>=pHash->nSlot ){
      int rc = fts5HashResize(pHash);
      if( rc!=SQLITE_OK ) return rc;
      iHash = fts5HashKey(pHash->nSlot, pToken, nToken);
    }

    p = (Fts5HashEntry*)sqlite3_malloc(nByte);
    if( !p ) return SQLITE_NOMEM;
    memset(p, 0, sizeof(Fts5HashEntry));
    p->nAlloc = nByte;

    memcpy(p->zKey, pToken, nToken);

    p->zKey[nToken] = '\0';
    p->nData = nToken + 1 + sizeof(Fts5HashEntry);
    p->nData += sqlite3PutVarint(&((u8*)p)[p->nData], iRowid);
    p->iSzPoslist = p->nData;
    p->nData += 1;
    p->iRowid = iRowid;
    p->pHashNext = pHash->aSlot[iHash];
    pHash->aSlot[iHash] = p;
    pHash->nEntry++;

#define FTS5_OPT_WORK_UNIT  1000  /* Number of leaf pages per optimize step */
#define FTS5_WORK_UNIT      64    /* Number of leaf pages in unit of work */

#define FTS5_MIN_DLIDX_SIZE 4     /* Add dlidx if this many empty pages */







/*
** Details:
**
** The %_data table managed by this module,
**
**     CREATE TABLE %_data(id INTEGER PRIMARY KEY, block BLOB);
**

**   representing the first docid on the page otherwise.
*/

/*
** Rowids for the averages and structure records in the %_data table.
*/
#define FTS5_AVERAGES_ROWID     1    /* Rowid used for the averages record */
#define FTS5_STRUCTURE_ROWID(iIdx) (10 + (iIdx))     /* For structure records */

/*
** Macros determining the rowids used by segment nodes. All nodes in all
** segments for all indexes (the regular FTS index and any prefix indexes)
** are stored in the %_data table with large positive rowids.
**
** The %_data table may contain up to (1<<FTS5_SEGMENT_INDEX_BITS) 

** a nodes page number is always one more than its left sibling.
**
** The rowid for a node is then found using the FTS5_SEGMENT_ROWID() macro
** below. The FTS5_SEGMENT_*_BITS macros define the number of bits used
** to encode the three FTS5_SEGMENT_ROWID() arguments. This module returns
** SQLITE_FULL and fails the current operation if they ever prove too small.
*/
#define FTS5_DATA_IDX_B     5     /* Max of 31 prefix indexes */
#define FTS5_DATA_ID_B     16     /* Max seg id number 65535 */
#define FTS5_DATA_HEIGHT_B  5     /* Max b-tree height of 32 */
#define FTS5_DATA_PAGE_B   31     /* Max page number of 2147483648 */

#define FTS5_SEGMENT_ROWID(idx, segid, height, pgno) (                         \
 ((i64)(idx)    << (FTS5_DATA_ID_B + FTS5_DATA_PAGE_B + FTS5_DATA_HEIGHT_B)) + \
 ((i64)(segid)  << (FTS5_DATA_PAGE_B + FTS5_DATA_HEIGHT_B)) +                  \
 ((i64)(height) << (FTS5_DATA_PAGE_B)) +                                       \
 ((i64)(pgno))                                                                 \
)

#if FTS5_MAX_PREFIX_INDEXES > ((1<<FTS5_DATA_IDX_B)-1) 
# error "FTS5_MAX_PREFIX_INDEXES is too large"
#endif

/*
** The height of segment b-trees is actually limited to one less than 
** (1<<HEIGHT_BITS). This is because the rowid address space for nodes
** with such a height is used by doclist indexes.
*/
#define FTS5_SEGMENT_MAX_HEIGHT ((1 << FTS5_DATA_HEIGHT_B)-1)

/*
** Maximum segments permitted in a single index 
*/
#define FTS5_MAX_SEGMENT 2000

/*
** The rowid for the doclist index associated with leaf page pgno of segment
** segid in index idx.
*/
#define FTS5_DOCLIST_IDX_ROWID(idx, segid, pgno) \
        FTS5_SEGMENT_ROWID(idx, segid, FTS5_SEGMENT_MAX_HEIGHT, pgno)

#ifdef SQLITE_DEBUG
int sqlite3Fts5Corrupt() { return SQLITE_CORRUPT_VTAB; }
#endif


/*

  char *zDataTbl;                 /* Name of %_data table */
  int nWorkUnit;                  /* Leaf pages in a "unit" of work */

  /*
  ** Variables related to the accumulation of tokens and doclists within the
  ** in-memory hash tables before they are flushed to disk.
  */
  Fts5Hash **apHash;              /* Array of hash tables */
  int nMaxPendingData;            /* Max pending data before flush to disk */
  int nPendingData;               /* Current bytes of pending data */
  i64 iWriteRowid;                /* Rowid for current doc being written */


  /* Error state. */
  int rc;                         /* Current error code */

  /* State used by the fts5DataXXX() functions. */
  sqlite3_blob *pReader;          /* RO incr-blob open on %_data table */
  sqlite3_stmt *pWriter;          /* "INSERT ... %_data VALUES(?,?)" */

*/
struct Fts5PageWriter {
  int pgno;                       /* Page number for this page */
  Fts5Buffer buf;                 /* Buffer containing page data */
  Fts5Buffer term;                /* Buffer containing previous term on page */
};
struct Fts5SegWriter {
  int iIdx;                       /* Index to write to */
  int iSegid;                     /* Segid to write to */
  int nWriter;                    /* Number of entries in aWriter */
  Fts5PageWriter *aWriter;        /* Array of PageWriter objects */
  i64 iPrevRowid;                 /* Previous docid written to current leaf */
  u8 bFirstRowidInDoclist;        /* True if next rowid is first in doclist */
  u8 bFirstRowidInPage;           /* True if next rowid is first in page */
  u8 bFirstTermInPage;            /* True if next term will be first in leaf */

**
**     For each rowid on the page corresponding to the current term, the
**     corresponding aRowidOffset[] entry is set to the byte offset of the
**     start of the "position-list-size" field within the page.
*/
struct Fts5SegIter {
  Fts5StructureSegment *pSeg;     /* Segment to iterate through */
  int iIdx;                       /* Byte offset within current leaf */
  int flags;                      /* Mask of configuration flags */
  int iLeafPgno;                  /* Current leaf page number */
  Fts5Data *pLeaf;                /* Current leaf data */
  int iLeafOffset;                /* Byte offset within current leaf */

  /* The page and offset from which the current term was read. The offset 
  ** is the offset of the first rowid in the current doclist.  */

struct Fts5BtreeIterLevel {
  Fts5NodeIter s;                 /* Iterator for the current node */
  Fts5Data *pData;                /* Data for the current node */
};
struct Fts5BtreeIter {
  Fts5Index *p;                   /* FTS5 backend object */
  Fts5StructureSegment *pSeg;     /* Iterate through this segment's b-tree */
  int iIdx;                       /* Index pSeg belongs to */
  int nLvl;                       /* Size of aLvl[] array */
  Fts5BtreeIterLevel *aLvl;       /* Level for each tier of b-tree */

  /* Output variables */
  Fts5Buffer term;                /* Current term */
  int iLeaf;                      /* Leaf containing terms >= current term */
  int nEmpty;                     /* Number of "empty" leaves following iLeaf */

    sqlite3_blob_close(p->pReader);
    p->pReader = 0;
  }
}
#endif

/*
** Remove all records associated with segment iSegid in index iIdx.
*/
static void fts5DataRemoveSegment(Fts5Index *p, int iIdx, int iSegid){
  i64 iFirst = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, 0);
  i64 iLast = FTS5_SEGMENT_ROWID(iIdx, iSegid+1, 0, 0)-1;
  fts5DataDelete(p, iFirst, iLast);
}

/*
** Release a reference to an Fts5Structure object returned by an earlier 
** call to fts5StructureRead() or fts5StructureDecode().
*/

    }else{
      *pRc = SQLITE_NOMEM;
    }
  }
}

/*
** Read, deserialize and return the structure record for index iIdx.
**
** The Fts5Structure.aLevel[] and each Fts5StructureLevel.aSeg[] array
** are over-allocated as described for function fts5StructureDecode() 
** above.
**
** If an error occurs, NULL is returned and an error code left in the
** Fts5Index handle. If an error has already occurred when this function
** is called, it is a no-op.
*/
static Fts5Structure *fts5StructureRead(Fts5Index *p, int iIdx){
  Fts5Config *pConfig = p->pConfig;
  Fts5Structure *pRet = 0;        /* Object to return */
  Fts5Data *pData;                /* %_data entry containing structure record */
  int iCookie;                    /* Configuration cookie */

  assert( iIdx<=pConfig->nPrefix );
  pData = fts5DataRead(p, FTS5_STRUCTURE_ROWID(iIdx));
  if( !pData ) return 0;
  p->rc = fts5StructureDecode(pData->p, pData->n, &iCookie, &pRet);

  if( p->rc==SQLITE_OK && pConfig->iCookie!=iCookie ){
    p->rc = sqlite3Fts5ConfigLoad(pConfig, iCookie);
  }

  }

  return nSegment;
}
#endif

/*
** Serialize and store the "structure" record for index iIdx.
**
** If an error occurs, leave an error code in the Fts5Index object. If an
** error has already occurred, this function is a no-op.
*/
static void fts5StructureWrite(Fts5Index *p, int iIdx, Fts5Structure *pStruct){
  if( p->rc==SQLITE_OK ){
    Fts5Buffer buf;               /* Buffer to serialize record into */
    int iLvl;                     /* Used to iterate through levels */
    int iCookie;                  /* Cookie value to store */

    assert( pStruct->nSegment==fts5StructureCountSegments(pStruct) );
    memset(&buf, 0, sizeof(Fts5Buffer));

        fts5BufferAppendVarint(&p->rc, &buf, pLvl->aSeg[iSeg].iSegid);
        fts5BufferAppendVarint(&p->rc, &buf, pLvl->aSeg[iSeg].nHeight);
        fts5BufferAppendVarint(&p->rc, &buf, pLvl->aSeg[iSeg].pgnoFirst);
        fts5BufferAppendVarint(&p->rc, &buf, pLvl->aSeg[iSeg].pgnoLast);
      }
    }

    fts5DataWrite(p, FTS5_STRUCTURE_ROWID(iIdx), buf.p, buf.n);
    fts5BufferFree(&buf);
  }
}

#if 0
static void fts5DebugStructure(int*,Fts5Buffer*,Fts5Structure*);
static void fts5PrintStructure(const char *zCaption, Fts5Structure *pStruct){

  return pIter->bEof;
}

static Fts5DlidxIter *fts5DlidxIterInit(
  Fts5Index *p,                   /* Fts5 Backend to iterate within */
  int bRev,                       /* True for ORDER BY ASC */
  int iIdx, int iSegid,           /* Segment iSegid within index iIdx */
  int iLeafPg                     /* Leaf page number to load dlidx for */
){
  Fts5DlidxIter *pIter;

  pIter = (Fts5DlidxIter*)fts5IdxMalloc(p, sizeof(Fts5DlidxIter));
  if( pIter==0 ) return 0;

  pIter->pData = fts5DataRead(p, FTS5_DOCLIST_IDX_ROWID(iIdx, iSegid, iLeafPg));
  if( pIter->pData==0 ){
    sqlite3_free(pIter);
    pIter = 0;
  }else{
    pIter->iLeafPgno = iLeafPg;
    if( bRev==0 ){
      fts5DlidxIterFirst(pIter);

  Fts5SegIter *pIter              /* Iterator to advance to next page */
){
  Fts5StructureSegment *pSeg = pIter->pSeg;
  fts5DataRelease(pIter->pLeaf);
  pIter->iLeafPgno++;
  if( pIter->iLeafPgno<=pSeg->pgnoLast ){
    pIter->pLeaf = fts5DataRead(p, 
        FTS5_SEGMENT_ROWID(pIter->iIdx, pSeg->iSegid, 0, pIter->iLeafPgno)
    );
  }else{
    pIter->pLeaf = 0;
  }
}

/*

  }
  iOff += sqlite3GetVarint(&a[iOff], (u64*)&pIter->iRowid);
  pIter->iLeafOffset = iOff;
}

/*
** Initialize the iterator object pIter to iterate through the entries in
** segment pSeg within index iIdx. The iterator is left pointing to the 
** first entry when this function returns.
**
** If an error occurs, Fts5Index.rc is set to an appropriate error code. If 
** an error has already occurred when this function is called, it is a no-op.
*/
static void fts5SegIterInit(
  Fts5Index *p,          
  int iIdx,                       /* Config.aHash[] index of FTS index */
  Fts5StructureSegment *pSeg,     /* Description of segment */
  Fts5SegIter *pIter              /* Object to populate */
){
  if( pSeg->pgnoFirst==0 ){
    /* This happens if the segment is being used as an input to an incremental
    ** merge and all data has already been "trimmed". See function
    ** fts5TrimSegments() for details. In this case leave the iterator empty.
    ** The caller will see the (pIter->pLeaf==0) and assume the iterator is
    ** at EOF already. */
    assert( pIter->pLeaf==0 );
    return;
  }

  if( p->rc==SQLITE_OK ){
    memset(pIter, 0, sizeof(*pIter));
    pIter->pSeg = pSeg;
    pIter->iIdx = iIdx;
    pIter->iLeafPgno = pSeg->pgnoFirst-1;
    fts5SegIterNextPage(p, pIter);
  }

  if( p->rc==SQLITE_OK ){
    u8 *a = pIter->pLeaf->p;
    pIter->iLeafOffset = fts5GetU16(&a[2]);

  fts5DataRelease(pIter->pLeaf);
  pIter->pLeaf = 0;
  while( p->rc==SQLITE_OK && pIter->iLeafPgno>pIter->iTermLeafPgno ){
    Fts5Data *pNew;
    pIter->iLeafPgno--;
    pNew = fts5DataRead(p, FTS5_SEGMENT_ROWID(
          pIter->iIdx, pIter->pSeg->iSegid, 0, pIter->iLeafPgno
    ));
    if( pNew ){
      if( pIter->iLeafPgno==pIter->iTermLeafPgno ){
        if( pIter->iTermLeafOffset<pNew->n ){
          pIter->pLeaf = pNew;
          pIter->iLeafOffset = pIter->iTermLeafOffset;
        }

          pIter->iRowid += iDelta;
        }
      }else if( pIter->pSeg==0 ){
        const u8 *pList = 0;
        const char *zTerm;
        int nList;
        if( 0==(pIter->flags & FTS5_SEGITER_ONETERM) ){
          sqlite3Fts5HashScanNext(p->apHash[0]);
          sqlite3Fts5HashScanEntry(p->apHash[0], &zTerm, &pList, &nList);
        }
        if( pList==0 ){
          fts5DataRelease(pIter->pLeaf);
          pIter->pLeaf = 0;
        }else{
          pIter->pLeaf->p = (u8*)pList;
          pIter->pLeaf->n = nList;

#define SWAPVAL(T, a, b) { T tmp; tmp=a; a=b; b=tmp; }

/*
** Iterator pIter currently points to the first rowid in a doclist. This
** function sets the iterator up so that iterates in reverse order through
** the doclist.
*/
static void fts5SegIterReverse(Fts5Index *p, int iIdx, Fts5SegIter *pIter){
  Fts5DlidxIter *pDlidx = pIter->pDlidx;
  Fts5Data *pLast = 0;
  int pgnoLast = 0;

  if( pDlidx ){
    /* If the doclist-iterator is already at EOF, then the current doclist
    ** contains no entries except those on the current page. */
    if( fts5DlidxIterEof(p, pDlidx)==0 ){
      int iSegid = pIter->pSeg->iSegid;
      pgnoLast = pDlidx->iLeafPgno;
      pLast = fts5DataRead(p, FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, pgnoLast));
    }else{
      pIter->iLeafOffset -= sqlite3Fts5GetVarintLen(pIter->nPos*2+pIter->bDel);
    }
  }else{
    int iOff;                               /* Byte offset within pLeaf */
    Fts5Data *pLeaf = pIter->pLeaf;         /* Current leaf data */

    if( iOff>=pLeaf->n ){
      int pgno;
      Fts5StructureSegment *pSeg = pIter->pSeg;

      /* The last rowid in the doclist may not be on the current page. Search
      ** forward to find the page containing the last rowid.  */
      for(pgno=pIter->iLeafPgno+1; !p->rc && pgno<=pSeg->pgnoLast; pgno++){
        i64 iAbs = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, pgno);
        Fts5Data *pNew = fts5DataRead(p, iAbs);
        if( pNew ){
          int iRowid, iTerm;
          fts5LeafHeader(pNew, &iRowid, &iTerm);
          if( iRowid ){
            SWAPVAL(Fts5Data*, pNew, pLast);
            pgnoLast = pgno;

    pIter->iLeafOffset = iOff;
  }

  fts5SegIterReverseInitPage(p, pIter);
}

/*
** Iterator pIter currently points to the first rowid of a doclist within
** index iIdx. There is a doclist-index associated with the final term on
** the current page. If the current term is the last term on the page, 
** load the doclist-index from disk and initialize an iterator at 
** (pIter->pDlidx).
*/
static void fts5SegIterLoadDlidx(Fts5Index *p, int iIdx, Fts5SegIter *pIter){
  int iSeg = pIter->pSeg->iSegid;
  int bRev = (pIter->flags & FTS5_SEGITER_REVERSE);
  Fts5Data *pLeaf = pIter->pLeaf; /* Current leaf data */

  assert( pIter->flags & FTS5_SEGITER_ONETERM );
  assert( pIter->pDlidx==0 );

      if( iDelta==0 ) return;
      assert_nc( iOff<pLeaf->n );
      iOff += fts5GetPoslistSize(&pLeaf->p[iOff], &nPos, &bDummy);
      iOff += nPos;
    }
  }

  pIter->pDlidx = fts5DlidxIterInit(p, bRev, iIdx, iSeg, pIter->iTermLeafPgno);
}

/*
** Initialize the object pIter to point to term pTerm/nTerm within segment
** pSeg, index iIdx. If there is no such term in the index, the iterator
** is set to EOF.
**
** If an error occurs, Fts5Index.rc is set to an appropriate error code. If 
** an error has already occurred when this function is called, it is a no-op.
*/
static void fts5SegIterSeekInit(
  Fts5Index *p,                   /* FTS5 backend */
  int iIdx,                       /* Config.aHash[] index of FTS index */
  const u8 *pTerm, int nTerm,     /* Term to seek to */
  int flags,                      /* Mask of FTS5INDEX_XXX flags */
  Fts5StructureSegment *pSeg,     /* Description of segment */
  Fts5SegIter *pIter              /* Object to populate */
){
  int iPg = 1;
  int h;
  int bGe = ((flags & FTS5INDEX_QUERY_PREFIX) && iIdx==0);
  int bDlidx = 0;                 /* True if there is a doclist-index */

  assert( bGe==0 || (flags & FTS5INDEX_QUERY_DESC)==0 );
  assert( pTerm && nTerm );
  memset(pIter, 0, sizeof(*pIter));
  pIter->pSeg = pSeg;
  pIter->iIdx = iIdx;

  /* This block sets stack variable iPg to the leaf page number that may
  ** contain term (pTerm/nTerm), if it is present in the segment. */
  for(h=pSeg->nHeight-1; h>0; h--){
    Fts5NodeIter node;              /* For iterating through internal nodes */
    i64 iRowid = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, h, iPg);
    Fts5Data *pNode = fts5DataRead(p, iRowid);
    if( pNode==0 ) break;

    fts5NodeIterInit(pNode->p, pNode->n, &node);
    assert( node.term.n==0 );

    iPg = node.iChild;

  if( p->rc==SQLITE_OK && bGe==0 ){
    pIter->flags |= FTS5_SEGITER_ONETERM;
    if( pIter->pLeaf ){
      if( flags & FTS5INDEX_QUERY_DESC ){
        pIter->flags |= FTS5_SEGITER_REVERSE;
      }
      if( bDlidx ){
        fts5SegIterLoadDlidx(p, iIdx, pIter);
      }
      if( flags & FTS5INDEX_QUERY_DESC ){
        fts5SegIterReverse(p, iIdx, pIter);
      }
    }
  }
}

/*
** Initialize the object pIter to point to term pTerm/nTerm within the
** in-memory hash table iIdx. If there is no such term in the table, the 
** iterator is set to EOF.
**
** If an error occurs, Fts5Index.rc is set to an appropriate error code. If 
** an error has already occurred when this function is called, it is a no-op.
*/
static void fts5SegIterHashInit(
  Fts5Index *p,                   /* FTS5 backend */
  int iIdx,                       /* Config.aHash[] index of FTS index */
  const u8 *pTerm, int nTerm,     /* Term to seek to */
  int flags,                      /* Mask of FTS5INDEX_XXX flags */
  Fts5SegIter *pIter              /* Object to populate */
){
  Fts5Hash *pHash = p->apHash[iIdx];
  const u8 *pList = 0;
  int nList = 0;
  const u8 *z = 0;
  int n = 0;

  assert( pHash );
  assert( p->rc==SQLITE_OK );

  if( pTerm==0 || (iIdx==0 && (flags & FTS5INDEX_QUERY_PREFIX)) ){
    p->rc = sqlite3Fts5HashScanInit(pHash, (const char*)pTerm, nTerm);
    sqlite3Fts5HashScanEntry(pHash, (const char**)&z, &pList, &nList);
    n = (z ? strlen((const char*)z) : 0);
  }else{
    pIter->flags |= FTS5_SEGITER_ONETERM;
    sqlite3Fts5HashQuery(pHash, (const char*)pTerm, nTerm, &pList, &nList);
    z = pTerm;
    n = nTerm;
  }

  if( pList ){
    Fts5Data *pLeaf;
    sqlite3Fts5BufferSet(&p->rc, &pIter->term, n, z);

**
** The iterator initially points to the first term/rowid entry in the 
** iterated data.
*/
static void fts5MultiIterNew(
  Fts5Index *p,                   /* FTS5 backend to iterate within */
  Fts5Structure *pStruct,         /* Structure of specific index */
  int iIdx,                       /* Config.aHash[] index of FTS index */
  int bSkipEmpty,                 /* True to ignore delete-keys */
  int flags,                      /* FTS5INDEX_QUERY_XXX flags */
  const u8 *pTerm, int nTerm,     /* Term to seek to (or NULL/0) */
  int iLevel,                     /* Level to iterate (-1 for all) */
  int nSegment,                   /* Number of segments to merge (iLevel>=0) */
  Fts5MultiSegIter **ppOut        /* New object */
){

  assert( (pTerm==0 && nTerm==0) || iLevel<0 );

  /* Allocate space for the new multi-seg-iterator. */
  if( p->rc==SQLITE_OK ){
    if( iLevel<0 ){
      assert( pStruct->nSegment==fts5StructureCountSegments(pStruct) );
      nSeg = pStruct->nSegment;
      nSeg += (p->apHash ? 1 : 0);
    }else{
      nSeg = MIN(pStruct->aLevel[iLevel].nSeg, nSegment);
    }
    for(nSlot=2; nSlot<nSeg; nSlot=nSlot*2);
  }

  *ppOut = pNew = fts5IdxMalloc(p, 

  pNew->aFirst = (Fts5CResult*)&pNew->aSeg[nSlot];
  pNew->bRev = (0!=(flags & FTS5INDEX_QUERY_DESC));
  pNew->bSkipEmpty = bSkipEmpty;

  /* Initialize each of the component segment iterators. */
  if( iLevel<0 ){
    Fts5StructureLevel *pEnd = &pStruct->aLevel[pStruct->nLevel];
    if( p->apHash ){
      /* Add a segment iterator for the current contents of the hash table. */
      Fts5SegIter *pIter = &pNew->aSeg[iIter++];
      fts5SegIterHashInit(p, iIdx, pTerm, nTerm, flags, pIter);
    }
    for(pLvl=&pStruct->aLevel[0]; pLvl<pEnd; pLvl++){
      for(iSeg=pLvl->nSeg-1; iSeg>=0; iSeg--){
        Fts5StructureSegment *pSeg = &pLvl->aSeg[iSeg];
        Fts5SegIter *pIter = &pNew->aSeg[iIter++];
        if( pTerm==0 ){
          fts5SegIterInit(p, iIdx, pSeg, pIter);
        }else{
          fts5SegIterSeekInit(p, iIdx, pTerm, nTerm, flags, pSeg, pIter);
        }
      }
    }
  }else{
    pLvl = &pStruct->aLevel[iLevel];
    for(iSeg=nSeg-1; iSeg>=0; iSeg--){
      fts5SegIterInit(p, iIdx, &pLvl->aSeg[iSeg], &pNew->aSeg[iIter++]);
    }
  }
  assert( iIter==nSeg );

  /* If the above was successful, each component iterators now points 
  ** to the first entry in its segment. In this case initialize the 
  ** aFirst[] array. Or, if an error has occurred, free the iterator

  int iOff = pSeg->iLeafOffset;

  memset(pIter, 0, sizeof(*pIter));
  /* If Fts5SegIter.pSeg is NULL, then this iterator iterates through data
  ** currently stored in a hash table. In this case there is no leaf-rowid
  ** to calculate.  */
  if( pSeg->pSeg ){
    int iId = pSeg->pSeg->iSegid;
    i64 rowid = FTS5_SEGMENT_ROWID(pSeg->iIdx, iId, 0, pSeg->iLeafPgno);
    pIter->iLeafRowid = rowid;
  }

  fts5DataReference(pLeaf);
  pIter->pLeaf = pLeaf;
  pIter->nRem = pSeg->nPos;
  pIter->n = MIN(pLeaf->n - iOff, pIter->nRem);

  return (int)iSegid;
}

/*
** Discard all data currently cached in the hash-tables.
*/
static void fts5IndexDiscardData(Fts5Index *p){
  assert( p->apHash || p->nPendingData==0 );
  if( p->apHash ){
    Fts5Config *pConfig = p->pConfig;
    int i;
    for(i=0; i<=pConfig->nPrefix; i++){
      sqlite3Fts5HashClear(p->apHash[i]);
    }
    p->nPendingData = 0;
  }
}

/*
** Return the size of the prefix, in bytes, that buffer (nNew/pNew) shares
** with buffer (nOld/pOld).

static void fts5WriteBtreeNEmpty(Fts5Index *p, Fts5SegWriter *pWriter){
  if( pWriter->nEmpty ){
    int bFlag = 0;
    Fts5PageWriter *pPg;
    pPg = &pWriter->aWriter[1];
    if( pWriter->nEmpty>=FTS5_MIN_DLIDX_SIZE ){
      i64 iKey = FTS5_DOCLIST_IDX_ROWID(
          pWriter->iIdx, pWriter->iSegid, 
          pWriter->aWriter[0].pgno - 1 - pWriter->nEmpty
      );
      assert( pWriter->cdlidx.n>0 );
      fts5DataWrite(p, iKey, pWriter->cdlidx.p, pWriter->cdlidx.n);
      bFlag = 1;
    }
    fts5BufferAppendVarint(&p->rc, &pPg->buf, bFlag);
    fts5BufferAppendVarint(&p->rc, &pPg->buf, pWriter->nEmpty);

    pPage = &pWriter->aWriter[iHeight];

    fts5WriteBtreeNEmpty(p, pWriter);

    if( pPage->buf.n>=p->pConfig->pgsz ){
      /* pPage will be written to disk. The term will be written into the
      ** parent of pPage.  */
      i64 iRowid = FTS5_SEGMENT_ROWID(
          pWriter->iIdx, pWriter->iSegid, iHeight, pPage->pgno
      );
      fts5DataWrite(p, iRowid, pPage->buf.p, pPage->buf.n);
      fts5BufferZero(&pPage->buf);
      fts5BufferZero(&pPage->term);
      fts5BufferAppendVarint(&p->rc, &pPage->buf, pPage[-1].pgno);
      pPage->pgno++;
    }else{
      int nPre = fts5PrefixCompress(pPage->term.n, pPage->term.p, nTerm, pTerm);

  if( pWriter->bFirstTermInPage ){
    /* No term was written to this page. */
    assert( 0==fts5GetU16(&pPage->buf.p[2]) );
    fts5WriteBtreeNoTerm(p, pWriter);
  }

  /* Write the current page to the db. */
  iRowid = FTS5_SEGMENT_ROWID(pWriter->iIdx, pWriter->iSegid, 0, pPage->pgno);
  fts5DataWrite(p, iRowid, pPage->buf.p, pPage->buf.n);

  /* Initialize the next page. */
  fts5BufferZero(&pPage->buf);
  fts5BufferAppendBlob(&p->rc, &pPage->buf, 4, zero);
  pPage->pgno++;

        fts5WriteBtreeNEmpty(p, pWriter);
      }
      *pnHeight = pWriter->nWriter;

      for(i=1; i<pWriter->nWriter; i++){
        Fts5PageWriter *pPg = &pWriter->aWriter[i];
        fts5DataWrite(p, 
            FTS5_SEGMENT_ROWID(pWriter->iIdx, pWriter->iSegid, i, pPg->pgno), 
            pPg->buf.p, pPg->buf.n
        );
      }
    }
  }
  for(i=0; i<pWriter->nWriter; i++){
    Fts5PageWriter *pPg = &pWriter->aWriter[i];
    fts5BufferFree(&pPg->term);
    fts5BufferFree(&pPg->buf);
  }
  sqlite3_free(pWriter->aWriter);
  sqlite3Fts5BufferFree(&pWriter->cdlidx);
}

static void fts5WriteInit(
  Fts5Index *p, 
  Fts5SegWriter *pWriter, 
  int iIdx, int iSegid
){
  memset(pWriter, 0, sizeof(Fts5SegWriter));
  pWriter->iIdx = iIdx;
  pWriter->iSegid = iSegid;

  pWriter->aWriter = (Fts5PageWriter*)fts5IdxMalloc(p,sizeof(Fts5PageWriter));
  if( pWriter->aWriter==0 ) return;
  pWriter->nWriter = 1;
  pWriter->aWriter[0].pgno = 1;
  pWriter->bFirstTermInPage = 1;
}

static void fts5WriteInitForAppend(
  Fts5Index *p,                   /* FTS5 backend object */
  Fts5SegWriter *pWriter,         /* Writer to initialize */
  int iIdx,                       /* Index segment is a part of */
  Fts5StructureSegment *pSeg      /* Segment object to append to */
){
  int nByte = pSeg->nHeight * sizeof(Fts5PageWriter);
  memset(pWriter, 0, sizeof(Fts5SegWriter));
  pWriter->iIdx = iIdx;
  pWriter->iSegid = pSeg->iSegid;
  pWriter->aWriter = (Fts5PageWriter*)fts5IdxMalloc(p, nByte);

  if( p->rc==SQLITE_OK ){
    int pgno = 1;
    int i;
    pWriter->nWriter = pSeg->nHeight;
    pWriter->aWriter[0].pgno = pSeg->pgnoLast+1;
    for(i=pSeg->nHeight-1; i>0; i--){
      i64 iRowid = FTS5_SEGMENT_ROWID(pWriter->iIdx, pWriter->iSegid, i, pgno);
      Fts5PageWriter *pPg = &pWriter->aWriter[i];
      pPg->pgno = pgno;
      fts5DataBuffer(p, &pPg->buf, iRowid);
      if( p->rc==SQLITE_OK ){
        Fts5NodeIter ss;
        fts5NodeIterInit(pPg->buf.p, pPg->buf.n, &ss);
        while( ss.aData ) fts5NodeIterNext(&p->rc, &ss);

    }else{
      int iOff = pSeg->iTermLeafOffset;     /* Offset on new first leaf page */
      i64 iLeafRowid;
      Fts5Data *pData;
      int iId = pSeg->pSeg->iSegid;
      u8 aHdr[4] = {0x00, 0x00, 0x00, 0x04};

      iLeafRowid = FTS5_SEGMENT_ROWID(pSeg->iIdx, iId, 0, pSeg->iTermLeafPgno);
      pData = fts5DataRead(p, iLeafRowid);
      if( pData ){
        fts5BufferZero(&buf);
        fts5BufferAppendBlob(&p->rc, &buf, sizeof(aHdr), aHdr);
        fts5BufferAppendVarint(&p->rc, &buf, pSeg->term.n);
        fts5BufferAppendBlob(&p->rc, &buf, pSeg->term.n, pSeg->term.p);
        fts5BufferAppendBlob(&p->rc, &buf, pData->n - iOff, &pData->p[iOff]);
        fts5DataRelease(pData);
        pSeg->pSeg->pgnoFirst = pSeg->iTermLeafPgno;
        fts5DataDelete(p, FTS5_SEGMENT_ROWID(pSeg->iIdx, iId, 0, 1),iLeafRowid);
        fts5DataWrite(p, iLeafRowid, buf.p, buf.n);
      }
    }
  }
  fts5BufferFree(&buf);
}

/*
**
*/
static void fts5IndexMergeLevel(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index to work on */
  Fts5Structure **ppStruct,       /* IN/OUT: Stucture of index iIdx */
  int iLvl,                       /* Level to read input from */
  int *pnRem                      /* Write up to this many output leaves */
){
  Fts5Structure *pStruct = *ppStruct;
  Fts5StructureLevel *pLvl = &pStruct->aLevel[iLvl];
  Fts5StructureLevel *pLvlOut;
  Fts5MultiSegIter *pIter = 0;    /* Iterator to read input data */
  int nRem = pnRem ? *pnRem : 0;  /* Output leaf pages left to write */
  int nInput;                     /* Number of input segments */
  Fts5SegWriter writer;           /* Writer object */
  Fts5StructureSegment *pSeg;     /* Output segment */
  Fts5Buffer term;
  int bRequireDoclistTerm = 0;    /* Doclist terminator (0x00) required */
  int bOldest;                    /* True if the output segment is the oldest */

  assert( iLvl<pStruct->nLevel );
  assert( pLvl->nMerge<=pLvl->nSeg );

  memset(&writer, 0, sizeof(Fts5SegWriter));
  memset(&term, 0, sizeof(Fts5Buffer));
  writer.iIdx = iIdx;
  if( pLvl->nMerge ){
    pLvlOut = &pStruct->aLevel[iLvl+1];
    assert( pLvlOut->nSeg>0 );
    nInput = pLvl->nMerge;
    fts5WriteInitForAppend(p, &writer, iIdx, &pLvlOut->aSeg[pLvlOut->nSeg-1]);
    pSeg = &pLvlOut->aSeg[pLvlOut->nSeg-1];
  }else{
    int iSegid = fts5AllocateSegid(p, pStruct);

    /* Extend the Fts5Structure object as required to ensure the output
    ** segment exists. */
    if( iLvl==pStruct->nLevel-1 ){
      fts5StructureAddLevel(&p->rc, ppStruct);
      pStruct = *ppStruct;
    }
    fts5StructureExtendLevel(&p->rc, pStruct, iLvl+1, 1, 0);
    if( p->rc ) return;
    pLvl = &pStruct->aLevel[iLvl];
    pLvlOut = &pStruct->aLevel[iLvl+1];

    fts5WriteInit(p, &writer, iIdx, iSegid);

    /* Add the new segment to the output level */
    pSeg = &pLvlOut->aSeg[pLvlOut->nSeg];
    pLvlOut->nSeg++;
    pSeg->pgnoFirst = 1;
    pSeg->iSegid = iSegid;
    pStruct->nSegment++;

    /* Read input from all segments in the input level */
    nInput = pLvl->nSeg;
  }
  bOldest = (pLvlOut->nSeg==1 && pStruct->nLevel==iLvl+2);

#if 0
fprintf(stdout, "merging %d segments from level %d!", nInput, iLvl);
fflush(stdout);
#endif

  assert( iLvl>=0 );
  for(fts5MultiIterNew(p, pStruct, iIdx, 0, 0, 0, 0, iLvl, nInput, &pIter);
      fts5MultiIterEof(p, pIter)==0;
      fts5MultiIterNext(p, pIter, 0, 0)
  ){
    Fts5SegIter *pSeg = &pIter->aSeg[ pIter->aFirst[1].iFirst ];
    Fts5ChunkIter sPos;           /* Used to iterate through position list */
    int nPos;                     /* position-list size field value */
    int nTerm;

  fts5WriteFinish(p, &writer, &pSeg->nHeight, &pSeg->pgnoLast);

  if( fts5MultiIterEof(p, pIter) ){
    int i;

    /* Remove the redundant segments from the %_data table */
    for(i=0; i<nInput; i++){
      fts5DataRemoveSegment(p, iIdx, pLvl->aSeg[i].iSegid);
    }

    /* Remove the redundant segments from the input level */
    if( pLvl->nSeg!=nInput ){
      int nMove = (pLvl->nSeg - nInput) * sizeof(Fts5StructureSegment);
      memmove(pLvl->aSeg, &pLvl->aSeg[nInput], nMove);
    }

  fts5MultiIterFree(p, pIter);
  fts5BufferFree(&term);
  if( pnRem ) *pnRem -= writer.nLeafWritten;
}

/*
** Do up to nPg pages of automerge work on index iIdx.
*/
static void fts5IndexMerge(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index to work on */
  Fts5Structure **ppStruct,       /* IN/OUT: Current structure of index */
  int nPg                         /* Pages of work to do */
){
  int nRem = nPg;
  Fts5Structure *pStruct = *ppStruct;
  while( nRem>0 && p->rc==SQLITE_OK ){
    int iLvl;                   /* To iterate through levels */

#endif

    if( nBest<p->pConfig->nAutomerge 
        && pStruct->aLevel[iBestLvl].nMerge==0 
      ){
      break;
    }
    fts5IndexMergeLevel(p, iIdx, &pStruct, iBestLvl, &nRem);
    if( p->rc==SQLITE_OK && pStruct->aLevel[iBestLvl].nMerge==0 ){
      fts5StructurePromote(p, iBestLvl+1, pStruct);
    }
  }
  *ppStruct = pStruct;
}

/*
** A total of nLeaf leaf pages of data has just been flushed to a level-0
** segments in index iIdx with structure pStruct. This function updates the
** write-counter accordingly and, if necessary, performs incremental merge
** work.
**
** If an error occurs, set the Fts5Index.rc error code. If an error has 
** already occurred, this function is a no-op.
*/
static void fts5IndexAutomerge(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index to work on */
  Fts5Structure **ppStruct,       /* IN/OUT: Current structure of index */
  int nLeaf                       /* Number of output leaves just written */
){
  if( p->rc==SQLITE_OK && p->pConfig->nAutomerge>0 ){
    Fts5Structure *pStruct = *ppStruct;
    i64 nWrite;                   /* Initial value of write-counter */
    int nWork;                    /* Number of work-quanta to perform */
    int nRem;                     /* Number of leaf pages left to write */

    /* Update the write-counter. While doing so, set nWork. */
    nWrite = pStruct->nWriteCounter;
    nWork = ((nWrite + nLeaf) / p->nWorkUnit) - (nWrite / p->nWorkUnit);
    pStruct->nWriteCounter += nLeaf;
    nRem = p->nWorkUnit * nWork * pStruct->nLevel;

    fts5IndexMerge(p, iIdx, ppStruct, nRem);
  }
}

static void fts5IndexCrisismerge(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index to work on */
  Fts5Structure **ppStruct        /* IN/OUT: Current structure of index */
){
  const int nCrisis = p->pConfig->nCrisisMerge;
  Fts5Structure *pStruct = *ppStruct;
  int iLvl = 0;

  assert( p->rc!=SQLITE_OK || pStruct->nLevel>0 );
  while( p->rc==SQLITE_OK && pStruct->aLevel[iLvl].nSeg>=nCrisis ){
    fts5IndexMergeLevel(p, iIdx, &pStruct, iLvl, 0);
    fts5StructurePromote(p, iLvl+1, pStruct);
    iLvl++;
  }
  *ppStruct = pStruct;
}

static int fts5IndexReturn(Fts5Index *p){

/*
** Flush the contents of in-memory hash table iHash to a new level-0 
** segment on disk. Also update the corresponding structure record.
**
** If an error occurs, set the Fts5Index.rc error code. If an error has 
** already occurred, this function is a no-op.
*/
static void fts5FlushOneHash(Fts5Index *p, int iHash, int *pnLeaf){
  Fts5Hash *pHash = p->apHash[iHash];
  Fts5Structure *pStruct;
  int iSegid;
  int pgnoLast = 0;                 /* Last leaf page number in segment */

  /* Obtain a reference to the index structure and allocate a new segment-id
  ** for the new level-0 segment.  */
  pStruct = fts5StructureRead(p, iHash);
  iSegid = fts5AllocateSegid(p, pStruct);

  if( iSegid ){
    const int pgsz = p->pConfig->pgsz;

    Fts5StructureSegment *pSeg;   /* New segment within pStruct */
    int nHeight;                  /* Height of new segment b-tree */
    Fts5Buffer *pBuf;             /* Buffer in which to assemble leaf page */
    const u8 *zPrev = 0;

    Fts5SegWriter writer;
    fts5WriteInit(p, &writer, iHash, iSegid);

    /* Pre-allocate the buffer used to assemble leaf pages to the target
    ** page size.  */
    assert( pgsz>0 );
    pBuf = &writer.aWriter[0].buf;
    fts5BufferGrow(&p->rc, pBuf, pgsz + 20);

      pSeg->pgnoLast = pgnoLast;
      pStruct->nSegment++;
    }
    fts5StructurePromote(p, 0, pStruct);
  }


  fts5IndexAutomerge(p, iHash, &pStruct, pgnoLast);
  fts5IndexCrisismerge(p, iHash, &pStruct);
  fts5StructureWrite(p, iHash, pStruct);
  fts5StructureRelease(pStruct);
}

/*
** Flush any data stored in the in-memory hash tables to the database.
*/
static void fts5IndexFlush(Fts5Index *p){
  Fts5Config *pConfig = p->pConfig;
  int i;                          /* Used to iterate through indexes */
  int nLeaf = 0;                  /* Number of leaves written */

  /* If an error has already occured this call is a no-op. */
  if( p->nPendingData==0 ) return;
  assert( p->apHash );

  /* Flush the terms and each prefix index to disk */
  for(i=0; i<=pConfig->nPrefix; i++){
    fts5FlushOneHash(p, i, &nLeaf);
  }
  p->nPendingData = 0;
}


int sqlite3Fts5IndexOptimize(Fts5Index *p){
  Fts5Config *pConfig = p->pConfig;

  int i;

  assert( p->rc==SQLITE_OK );
  fts5IndexFlush(p);
  for(i=0; i<=pConfig->nPrefix; i++){
    Fts5Structure *pStruct = fts5StructureRead(p, i);
    Fts5Structure *pNew = 0;
    int nSeg = 0;
    if( pStruct ){
      assert( pStruct->nSegment==fts5StructureCountSegments(pStruct) );
      nSeg = pStruct->nSegment;
      if( nSeg>1 ){
        int nByte = sizeof(Fts5Structure);
        nByte += (pStruct->nLevel+1) * sizeof(Fts5StructureLevel);
        pNew = (Fts5Structure*)sqlite3Fts5MallocZero(&p->rc, nByte);
      }
    }
    if( pNew ){
      Fts5StructureLevel *pLvl;
      int nByte = nSeg * sizeof(Fts5StructureSegment);
      pNew->nLevel = pStruct->nLevel+1;
      pNew->nWriteCounter = pStruct->nWriteCounter;
      pLvl = &pNew->aLevel[pStruct->nLevel];
      pLvl->aSeg = (Fts5StructureSegment*)sqlite3Fts5MallocZero(&p->rc, nByte);
      if( pLvl->aSeg ){
        int iLvl, iSeg;
        int iSegOut = 0;
        for(iLvl=0; iLvl<pStruct->nLevel; iLvl++){
          for(iSeg=0; iSeg<pStruct->aLevel[iLvl].nSeg; iSeg++){
            pLvl->aSeg[iSegOut] = pStruct->aLevel[iLvl].aSeg[iSeg];
            iSegOut++;
          }
        }
        pNew->nSegment = pLvl->nSeg = nSeg;
      }else{
        sqlite3_free(pNew);
        pNew = 0;
      }
    }

    if( pNew ){
      int iLvl = pNew->nLevel-1;
      while( p->rc==SQLITE_OK && pNew->aLevel[iLvl].nSeg>0 ){
        int nRem = FTS5_OPT_WORK_UNIT;
        fts5IndexMergeLevel(p, i, &pNew, iLvl, &nRem);
      }

      fts5StructureWrite(p, i, pNew);
      fts5StructureRelease(pNew);
    }

    fts5StructureRelease(pStruct);
  }

  return fts5IndexReturn(p); 
}

int sqlite3Fts5IndexMerge(Fts5Index *p, int nMerge){
  Fts5Structure *pStruct;

  pStruct = fts5StructureRead(p, 0);
  fts5IndexMerge(p, 0, &pStruct, nMerge);
  fts5StructureWrite(p, 0, pStruct);
  fts5StructureRelease(pStruct);

  return fts5IndexReturn(p);
}


/*

  Fts5IndexIter *pIter            /* Populate this object */
){
  Fts5Structure *pStruct;
  Fts5Buffer *aBuf;
  const int nBuf = 32;

  aBuf = (Fts5Buffer*)fts5IdxMalloc(p, sizeof(Fts5Buffer)*nBuf);
  pStruct = fts5StructureRead(p, 0);

  if( aBuf && pStruct ){
    Fts5DoclistIter *pDoclist;
    int i;
    i64 iLastRowid = 0;
    Fts5MultiSegIter *p1 = 0;     /* Iterator used to gather data from index */
    Fts5Buffer doclist;

    memset(&doclist, 0, sizeof(doclist));
    for(fts5MultiIterNew(p, pStruct, 0, 1, 1, pToken, nToken, -1, 0, &p1);
        fts5MultiIterEof(p, p1)==0;
        fts5MultiIterNext(p, p1, 0, 0)
    ){
      i64 iRowid = fts5MultiIterRowid(p1);
      int nTerm;
      const u8 *pTerm = fts5MultiIterTerm(p1, &nTerm);
      assert( memcmp(pToken, pTerm, MIN(nToken, nTerm))<=0 );

/*
** Indicate that all subsequent calls to sqlite3Fts5IndexWrite() pertain
** to the document with rowid iRowid.
*/
int sqlite3Fts5IndexBeginWrite(Fts5Index *p, i64 iRowid){
  assert( p->rc==SQLITE_OK );

  /* Allocate hash tables if they have not already been allocated */
  if( p->apHash==0 ){
    int i;
    int rc = SQLITE_OK;
    int nHash = p->pConfig->nPrefix + 1;
    Fts5Hash **apNew;

    apNew = (Fts5Hash**)sqlite3Fts5MallocZero(&rc, sizeof(Fts5Hash*)*nHash);
    for(i=0; rc==SQLITE_OK && i<nHash; i++){
      rc = sqlite3Fts5HashNew(&apNew[i], &p->nPendingData);
    }
    if( rc==SQLITE_OK ){
      p->apHash = apNew;
    }else{
      if( apNew ){
        for(i=0; i<nHash; i++){
          sqlite3Fts5HashFree(apNew[i]);
        }
        sqlite3_free(apNew);
      }
      return rc;
    }
  }

  if( iRowid<=p->iWriteRowid || (p->nPendingData > p->nMaxPendingData) ){
    assert( p->rc==SQLITE_OK );
    fts5IndexFlush(p);
  }
  p->iWriteRowid = iRowid;
  return fts5IndexReturn(p);
}

/*

/*
** The %_data table is completely empty when this function is called. This
** function populates it with the initial structure objects for each index,
** and the initial version of the "averages" record (a zero-byte blob).
*/
int sqlite3Fts5IndexReinit(Fts5Index *p){
  int i;
  Fts5Structure s;

  memset(&s, 0, sizeof(Fts5Structure));
  for(i=0; i<p->pConfig->nPrefix+1; i++){
    fts5StructureWrite(p, i, &s);
  }
  if( p->rc==SQLITE_OK ){
    p->rc = sqlite3Fts5IndexSetAverages(p, (const u8*)"", 0);
  }



  return fts5IndexReturn(p);
}

/*
** Open a new Fts5Index handle. If the bCreate argument is true, create
** and initialize the underlying %_data table.

*/
int sqlite3Fts5IndexClose(Fts5Index *p){
  int rc = SQLITE_OK;
  if( p ){
    assert( p->pReader==0 );
    sqlite3_finalize(p->pWriter);
    sqlite3_finalize(p->pDeleter);
    if( p->apHash ){
      int i;
      for(i=0; i<=p->pConfig->nPrefix; i++){
        sqlite3Fts5HashFree(p->apHash[i]);
      }
      sqlite3_free(p->apHash);
    }
    sqlite3_free(p->zDataTbl);
    sqlite3_free(p);
  }
  return rc;
}

/*

int sqlite3Fts5IndexWrite(
  Fts5Index *p,                   /* Index to write to */
  int iCol,                       /* Column token appears in (-ve -> delete) */
  int iPos,                       /* Position of token within column */
  const char *pToken, int nToken  /* Token to add or remove to or from index */
){
  int i;                          /* Used to iterate through indexes */
  int rc;                         /* Return code */
  Fts5Config *pConfig = p->pConfig;

  assert( p->rc==SQLITE_OK );

  /* Add the new token to the main terms hash table. And to each of the
  ** prefix hash tables that it is large enough for. */
  rc = sqlite3Fts5HashWrite(
      p->apHash[0], p->iWriteRowid, iCol, iPos, pToken, nToken
  );

  for(i=0; i<pConfig->nPrefix && rc==SQLITE_OK; i++){
    int nByte = fts5IndexCharlenToBytelen(pToken, nToken, pConfig->aPrefix[i]);
    if( nByte ){
      rc = sqlite3Fts5HashWrite(
          p->apHash[i+1], p->iWriteRowid, iCol, iPos, pToken, nByte
      );
    }
  }

  return rc;
}

/*
** Open a new iterator to iterate though all docids that match the 
** specified token or token prefix.
*/
int sqlite3Fts5IndexQuery(
  Fts5Index *p,                   /* FTS index to query */
  const char *pToken, int nToken, /* Token (or prefix) to query for */
  int flags,                      /* Mask of FTS5INDEX_QUERY_X flags */
  Fts5IndexIter **ppIter          /* OUT: New iterator object */
){
  Fts5Config *pConfig = p->pConfig;
  Fts5IndexIter *pRet;
  int iIdx = 0;






  if( flags & FTS5INDEX_QUERY_PREFIX ){
    if( flags & FTS5INDEX_QUERY_TEST_NOIDX ){
      iIdx = 1+pConfig->nPrefix;
    }else{
      int nChar = fts5IndexCharlen(pToken, nToken);
      for(iIdx=1; iIdx<=pConfig->nPrefix; iIdx++){
        if( pConfig->aPrefix[iIdx-1]==nChar ) break;
      }
    }
  }

  pRet = (Fts5IndexIter*)sqlite3Fts5MallocZero(&p->rc, sizeof(Fts5IndexIter));
  if( pRet ){
    memset(pRet, 0, sizeof(Fts5IndexIter));

    pRet->pIndex = p;
    if( iIdx<=pConfig->nPrefix ){

      pRet->pStruct = fts5StructureRead(p, iIdx);
      if( pRet->pStruct ){

        fts5MultiIterNew(p, pRet->pStruct, 
            iIdx, 1, flags, (const u8*)pToken, nToken, -1, 0, &pRet->pMulti
        );
      }
    }else{
      int bDesc = (flags & FTS5INDEX_QUERY_DESC)!=0;

      fts5SetupPrefixIter(p, bDesc, (const u8*)pToken, nToken, pRet);
    }
  }

  if( p->rc ){
    sqlite3Fts5IterClose(pRet);
    pRet = 0;
  }
  *ppIter = pRet;

  return fts5IndexReturn(p);
}

/*
** Return true if the iterator passed as the only argument is at EOF.
*/
int sqlite3Fts5IterEof(Fts5IndexIter *pIter){

** Set the 32-bit cookie value stored at the start of all structure 
** records to the value passed as the second argument.
**
** Return SQLITE_OK if successful, or an SQLite error code if an error
** occurs.
*/
int sqlite3Fts5IndexSetCookie(Fts5Index *p, int iNew){
  int rc = SQLITE_OK;
  Fts5Config *pConfig = p->pConfig;
  u8 aCookie[4];
  int i;

  assert( p->rc==SQLITE_OK );

  sqlite3Fts5Put32(aCookie, iNew);
  for(i=0; rc==SQLITE_OK && i<=pConfig->nPrefix; i++){
    sqlite3_blob *pBlob = 0;
    i64 iRowid = FTS5_STRUCTURE_ROWID(i);
    rc = sqlite3_blob_open(
        pConfig->db, pConfig->zDb, p->zDataTbl, "block", iRowid, 1, &pBlob
    );
    if( rc==SQLITE_OK ){
      sqlite3_blob_write(pBlob, aCookie, 4, 0);
      rc = sqlite3_blob_close(pBlob);
    }
  }

  return rc;
}

int sqlite3Fts5IndexLoadConfig(Fts5Index *p){
  Fts5Structure *pStruct;
  pStruct = fts5StructureRead(p, 0);
  fts5StructureRelease(pStruct);
  return fts5IndexReturn(p);
}


/*************************************************************************
**************************************************************************
** Below this point is the implementation of the integrity-check 
** functionality.
*/

/*
** Return a simple checksum value based on the arguments.
*/
static u64 fts5IndexEntryCksum(
  i64 iRowid, 
  int iCol, 
  int iPos, 

  const char *pTerm, 
  int nTerm
){
  int i;
  u64 ret = iRowid;
  ret += (ret<<3) + iCol;
  ret += (ret<<3) + iPos;

  for(i=0; i<nTerm; i++) ret += (ret<<3) + pTerm[i];
  return ret;
}

static void fts5BtreeIterInit(
  Fts5Index *p, 
  int iIdx,
  Fts5StructureSegment *pSeg, 
  Fts5BtreeIter *pIter
){
  int nByte;
  int i;
  nByte = sizeof(pIter->aLvl[0]) * (pSeg->nHeight-1);
  memset(pIter, 0, sizeof(*pIter));
  if( nByte ){
    pIter->aLvl = (Fts5BtreeIterLevel*)fts5IdxMalloc(p, nByte);
  }
  if( p->rc==SQLITE_OK ){
    pIter->nLvl = pSeg->nHeight-1;
    pIter->iIdx = iIdx;
    pIter->p = p;
    pIter->pSeg = pSeg;
  }
  for(i=0; p->rc==SQLITE_OK && i<pIter->nLvl; i++){
    i64 iRowid = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, i+1, 1);
    Fts5Data *pData;
    pIter->aLvl[i].pData = pData = fts5DataRead(p, iRowid);
    if( pData ){
      fts5NodeIterInit(pData->p, pData->n, &pIter->aLvl[i].s);
    }
  }

  }
  if( i==pIter->nLvl || p->rc ){
    pIter->bEof = 1;
  }else{
    int iSegid = pIter->pSeg->iSegid;
    for(i--; i>=0; i--){
      Fts5BtreeIterLevel *pLvl = &pIter->aLvl[i];
      i64 iRowid = FTS5_SEGMENT_ROWID(pIter->iIdx,iSegid,i+1,pLvl[1].s.iChild);
      pLvl->pData = fts5DataRead(p, iRowid);
      if( pLvl->pData ){
        fts5NodeIterInit(pLvl->pData->p, pLvl->pData->n, &pLvl->s);
      }
    }
  }

/*
** This function is purely an internal test. It does not contribute to 
** FTS functionality, or even the integrity-check, in any way.
**
** Instead, it tests that the same set of pgno/rowid combinations are 
** visited regardless of whether the doclist-index identified by parameters
** iIdx/iSegid/iLeaf is iterated in forwards or reverse order.
*/
#ifdef SQLITE_DEBUG
static void fts5DlidxIterTestReverse(
  Fts5Index *p, 
  int iIdx,                       /* Index to load doclist-index from */
  int iSegid,                     /* Segment id to load from */
  int iLeaf                       /* Load doclist-index for this leaf */
){
  Fts5DlidxIter *pDlidx = 0;
  i64 cksum1 = 13;
  i64 cksum2 = 13;

  for(pDlidx=fts5DlidxIterInit(p, 0, iIdx, iSegid, iLeaf);
      fts5DlidxIterEof(p, pDlidx)==0;
      fts5DlidxIterNext(pDlidx)
  ){
    assert( pDlidx->iLeafPgno>iLeaf );
    cksum1 = (cksum1 ^ ( (i64)(pDlidx->iLeafPgno) << 32 ));
    cksum1 = (cksum1 ^ pDlidx->iRowid);
  }
  fts5DlidxIterFree(pDlidx);
  pDlidx = 0;

  for(pDlidx=fts5DlidxIterInit(p, 1, iIdx, iSegid, iLeaf);
      fts5DlidxIterEof(p, pDlidx)==0;
      fts5DlidxIterPrev(pDlidx)
  ){
    assert( pDlidx->iLeafPgno>iLeaf );
    cksum2 = (cksum2 ^ ( (i64)(pDlidx->iLeafPgno) << 32 ));
    cksum2 = (cksum2 ^ pDlidx->iRowid);
  }
  fts5DlidxIterFree(pDlidx);
  pDlidx = 0;

  if( p->rc==SQLITE_OK && cksum1!=cksum2 ) p->rc = FTS5_CORRUPT; 
}
#else
# define fts5DlidxIterTestReverse(w,x,y,z)
#endif

static void fts5IndexIntegrityCheckSegment(
  Fts5Index *p,                   /* FTS5 backend object */
  int iIdx,                       /* Index that pSeg is a part of */
  Fts5StructureSegment *pSeg      /* Segment to check internal consistency */
){
  Fts5BtreeIter iter;             /* Used to iterate through b-tree hierarchy */

  if( pSeg->pgnoFirst==0 ) return;

  /* Iterate through the b-tree hierarchy.  */
  for(fts5BtreeIterInit(p, iIdx, pSeg, &iter);
      p->rc==SQLITE_OK && iter.bEof==0;
      fts5BtreeIterNext(&iter)
  ){
    i64 iRow;                     /* Rowid for this leaf */
    Fts5Data *pLeaf;              /* Data for this leaf */
    int iOff;                     /* Offset of first term on leaf */
    int i;                        /* Used to iterate through empty leaves */

    /* If the leaf in question has already been trimmed from the segment, 
    ** ignore this b-tree entry. Otherwise, load it into memory. */
    if( iter.iLeaf<pSeg->pgnoFirst ) continue;
    iRow = FTS5_SEGMENT_ROWID(iIdx, pSeg->iSegid, 0, iter.iLeaf);
    pLeaf = fts5DataRead(p, iRow);
    if( pLeaf==0 ) break;

    /* Check that the leaf contains at least one term, and that it is equal
    ** to or larger than the split-key in iter.term.  */
    iOff = fts5GetU16(&pLeaf->p[2]);
    if( iOff==0 ){

    if( iter.bDlidx ){
      Fts5DlidxIter *pDlidx = 0;  /* For iterating through doclist index */
      int iPrevLeaf = iter.iLeaf;
      int iSegid = pSeg->iSegid;
      int iPg;
      i64 iKey;

      for(pDlidx=fts5DlidxIterInit(p, 0, iIdx, iSegid, iter.iLeaf);
          fts5DlidxIterEof(p, pDlidx)==0;
          fts5DlidxIterNext(pDlidx)
      ){

        /* Check any rowid-less pages that occur before the current leaf. */
        for(iPg=iPrevLeaf+1; iPg<pDlidx->iLeafPgno; iPg++){
          iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, iPg);
          pLeaf = fts5DataRead(p, iKey);
          if( pLeaf ){
            if( fts5GetU16(&pLeaf->p[0])!=0 ) p->rc = FTS5_CORRUPT;
            fts5DataRelease(pLeaf);
          }
        }
        iPrevLeaf = pDlidx->iLeafPgno;

        /* Check that the leaf page indicated by the iterator really does
        ** contain the rowid suggested by the same. */
        iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, pDlidx->iLeafPgno);
        pLeaf = fts5DataRead(p, iKey);
        if( pLeaf ){
          i64 iRowid;
          int iRowidOff = fts5GetU16(&pLeaf->p[0]);
          getVarint(&pLeaf->p[iRowidOff], (u64*)&iRowid);
          if( iRowid!=pDlidx->iRowid ) p->rc = FTS5_CORRUPT;
          fts5DataRelease(pLeaf);
        }

      }

      for(iPg=iPrevLeaf+1; iPg<=(iter.iLeaf + iter.nEmpty); iPg++){
        iKey = FTS5_SEGMENT_ROWID(iIdx, iSegid, 0, iPg);
        pLeaf = fts5DataRead(p, iKey);
        if( pLeaf ){
          if( fts5GetU16(&pLeaf->p[0])!=0 ) p->rc = FTS5_CORRUPT;
          fts5DataRelease(pLeaf);
        }
      }

      fts5DlidxIterFree(pDlidx);
      fts5DlidxIterTestReverse(p, iIdx, iSegid, iter.iLeaf);
    }
  }

  /* Either iter.iLeaf must be the rightmost leaf-page in the segment, or 
  ** else the segment has been completely emptied by an ongoing merge
  ** operation. */
  if( p->rc==SQLITE_OK 
   && iter.iLeaf!=pSeg->pgnoLast 
   && (pSeg->pgnoFirst || pSeg->pgnoLast) 
  ){
    p->rc = FTS5_CORRUPT;
  }

  fts5BtreeIterFree(&iter);
}


static int fts5QueryCksum(
  Fts5Index *p,

  const char *z,
  int n,
  int flags,
  u64 *pCksum
){
  u64 cksum = *pCksum;
  Fts5IndexIter *pIdxIter = 0;
  int rc = sqlite3Fts5IndexQuery(p, z, n, flags, &pIdxIter);

  while( rc==SQLITE_OK && 0==sqlite3Fts5IterEof(pIdxIter) ){
    const u8 *pPos;
    int nPos;
    i64 rowid = sqlite3Fts5IterRowid(pIdxIter);
    rc = sqlite3Fts5IterPoslist(pIdxIter, &pPos, &nPos);
    if( rc==SQLITE_OK ){
      Fts5PoslistReader sReader;
      for(sqlite3Fts5PoslistReaderInit(-1, pPos, nPos, &sReader);
          sReader.bEof==0;
          sqlite3Fts5PoslistReaderNext(&sReader)
      ){
        int iCol = FTS5_POS2COLUMN(sReader.iPos);
        int iOff = FTS5_POS2OFFSET(sReader.iPos);
        cksum ^= fts5IndexEntryCksum(rowid, iCol, iOff, z, n);
      }
      rc = sqlite3Fts5IterNext(pIdxIter);
    }
  }
  sqlite3Fts5IterClose(pIdxIter);

  *pCksum = cksum;

**
** Return SQLITE_CORRUPT if any of the internal checks fail, or if the
** checksum does not match. Return SQLITE_OK if all checks pass without
** error, or some other SQLite error code if another error (e.g. OOM)
** occurs.
*/
int sqlite3Fts5IndexIntegrityCheck(Fts5Index *p, u64 cksum){
  Fts5Config *pConfig = p->pConfig;
  int iIdx;                       /* Used to iterate through indexes */
  u64 cksum2 = 0;                 /* Checksum based on contents of indexes */
  u64 cksum3 = 0;                 /* Checksum based on contents of indexes */
  Fts5Buffer term = {0,0,0};      /* Buffer used to hold most recent term */
  Fts5Buffer poslist = {0,0,0};   /* Buffer used to hold a poslist */






  /* Check that the internal nodes of each segment match the leaves */
  for(iIdx=0; p->rc==SQLITE_OK && iIdx<=pConfig->nPrefix; iIdx++){
    Fts5Structure *pStruct = fts5StructureRead(p, iIdx);
    if( pStruct ){
      int iLvl, iSeg;
      for(iLvl=0; iLvl<pStruct->nLevel; iLvl++){
        for(iSeg=0; iSeg<pStruct->aLevel[iLvl].nSeg; iSeg++){
          Fts5StructureSegment *pSeg = &pStruct->aLevel[iLvl].aSeg[iSeg];
          fts5IndexIntegrityCheckSegment(p, iIdx, pSeg);
        }
      }
    }
    fts5StructureRelease(pStruct);
  }

  /* The cksum argument passed to this function is a checksum calculated
  ** based on all expected entries in the FTS index (including prefix index
  ** entries). This block checks that a checksum calculated based on the
  ** actual contents of FTS index is identical.
  **
  ** Two versions of the same checksum are calculated. The first (stack
  ** variable cksum2) based on entries extracted from the full-text index
  ** while doing a linear scan of each individual index in turn. 
  **
  ** As each term visited by the linear scans, a separate query for the
  ** same term is performed. cksum3 is calculated based on the entries
  ** extracted by these queries.
  */
  for(iIdx=0; iIdx<=pConfig->nPrefix; iIdx++){
    Fts5MultiSegIter *pIter;
    Fts5Structure *pStruct = fts5StructureRead(p, iIdx);
    for(fts5MultiIterNew(p, pStruct, iIdx, 0, 0, 0, 0, -1, 0, &pIter);
        fts5MultiIterEof(p, pIter)==0;
        fts5MultiIterNext(p, pIter, 0, 0)
    ){
      int n;                      /* Size of term in bytes */
      i64 iPos = 0;               /* Position read from poslist */
      int iOff = 0;               /* Offset within poslist */
      i64 iRowid = fts5MultiIterRowid(pIter);
      char *z = (char*)fts5MultiIterTerm(pIter, &n);

      poslist.n = 0;
      fts5MultiIterPoslist(p, pIter, 0, &poslist);
      while( 0==sqlite3Fts5PoslistNext64(poslist.p, poslist.n, &iOff, &iPos) ){
        int iCol = FTS5_POS2COLUMN(iPos);
        int iTokOff = FTS5_POS2OFFSET(iPos);
        cksum2 ^= fts5IndexEntryCksum(iRowid, iCol, iTokOff, z, n);
      }

      /* If this is a new term, query for it. Update cksum3 with the results. */
      if( p->rc==SQLITE_OK && (term.n!=n || memcmp(term.p, z, n)) ){


        int rc;
        int flags = (iIdx==0 ? 0 : FTS5INDEX_QUERY_PREFIX);

        u64 ck1 = 0;
        u64 ck2 = 0;

        /* Check that the results returned for ASC and DESC queries are
        ** the same. If not, call this corruption.  */
        rc = fts5QueryCksum(p, z, n, flags, &ck1);
        if( rc==SQLITE_OK ){
          rc = fts5QueryCksum(p, z, n, flags|FTS5INDEX_QUERY_DESC, &ck2);

        }
        if( rc==SQLITE_OK && ck1!=ck2 ) rc = FTS5_CORRUPT;

        /* If this is a prefix query, check that the results returned if the
        ** the index is disabled are the same. In both ASC and DESC order. */
        if( iIdx>0 && rc==SQLITE_OK ){
          int f = flags|FTS5INDEX_QUERY_TEST_NOIDX;
          ck2 = 0;
          rc = fts5QueryCksum(p, z, n, f, &ck2);
          if( rc==SQLITE_OK && ck1!=ck2 ) rc = FTS5_CORRUPT;
        }
        if( iIdx>0 && rc==SQLITE_OK ){
          int f = flags|FTS5INDEX_QUERY_TEST_NOIDX|FTS5INDEX_QUERY_DESC;
          ck2 = 0;
          rc = fts5QueryCksum(p, z, n, f, &ck2);
          if( rc==SQLITE_OK && ck1!=ck2 ) rc = FTS5_CORRUPT;
        }

        cksum3 ^= ck1;
        fts5BufferSet(&rc, &term, n, (const u8*)z);
        p->rc = rc;
      }
    }
    fts5MultiIterFree(p, pIter);
    fts5StructureRelease(pStruct);
  }
  if( p->rc==SQLITE_OK && cksum!=cksum2 ) p->rc = FTS5_CORRUPT;
  if( p->rc==SQLITE_OK && cksum!=cksum3 ) p->rc = FTS5_CORRUPT;


  fts5BufferFree(&term);
  fts5BufferFree(&poslist);
  return fts5IndexReturn(p);
}


/*

  int iCol,                       /* Column term appears in */
  int iPos,                       /* Position term appears in */
  const char *pTerm, int nTerm    /* Term at iPos */
){
  u64 ret = 0;                    /* Return value */
  int iIdx;                       /* For iterating through indexes */

  ret = fts5IndexEntryCksum(iRowid, iCol, iPos, pTerm, nTerm);

  for(iIdx=0; iIdx<pConfig->nPrefix; iIdx++){
    int nByte = fts5IndexCharlenToBytelen(pTerm, nTerm, pConfig->aPrefix[iIdx]);
    if( nByte ){
      ret ^= fts5IndexEntryCksum(iRowid, iCol, iPos, pTerm, nByte);
    }
  }

  return ret;
}

/*************************************************************************
**************************************************************************
** Below this point is the implementation of the fts5_decode() scalar
** function only.
*/

/*
** Decode a segment-data rowid from the %_data table. This function is
** the opposite of macro FTS5_SEGMENT_ROWID().
*/
static void fts5DecodeRowid(
  i64 iRowid,                     /* Rowid from %_data table */
  int *piIdx,                     /* OUT: Index */
  int *piSegid,                   /* OUT: Segment id */
  int *piHeight,                  /* OUT: Height */
  int *piPgno                     /* OUT: Page number */
){
  *piPgno = (int)(iRowid & (((i64)1 << FTS5_DATA_PAGE_B) - 1));
  iRowid >>= FTS5_DATA_PAGE_B;

  *piHeight = (int)(iRowid & (((i64)1 << FTS5_DATA_HEIGHT_B) - 1));
  iRowid >>= FTS5_DATA_HEIGHT_B;

  *piSegid = (int)(iRowid & (((i64)1 << FTS5_DATA_ID_B) - 1));
  iRowid >>= FTS5_DATA_ID_B;

  *piIdx = (int)(iRowid & (((i64)1 << FTS5_DATA_IDX_B) - 1));
}

static void fts5DebugRowid(int *pRc, Fts5Buffer *pBuf, i64 iKey){
  int iIdx,iSegid,iHeight,iPgno;  /* Rowid compenents */
  fts5DecodeRowid(iKey, &iIdx, &iSegid, &iHeight, &iPgno);

  if( iSegid==0 ){
    if( iKey==FTS5_AVERAGES_ROWID ){
      sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "(averages) ");
    }else{
      sqlite3Fts5BufferAppendPrintf(pRc, pBuf, 
          "{structure idx=%d}", (int)(iKey-10)
      );
    }
  }
  else if( iHeight==FTS5_SEGMENT_MAX_HEIGHT ){
    sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "(dlidx idx=%d segid=%d pgno=%d)",
        iIdx, iSegid, iPgno
    );
  }else{
    sqlite3Fts5BufferAppendPrintf(pRc, pBuf, "(idx=%d segid=%d h=%d pgno=%d)",
        iIdx, iSegid, iHeight, iPgno
    );
  }
}

static void fts5DebugStructure(
  int *pRc,                       /* IN/OUT: error code */
  Fts5Buffer *pBuf,

*/
static void fts5DecodeFunction(
  sqlite3_context *pCtx,          /* Function call context */
  int nArg,                       /* Number of args (always 2) */
  sqlite3_value **apVal           /* Function arguments */
){
  i64 iRowid;                     /* Rowid for record being decoded */
  int iIdx,iSegid,iHeight,iPgno;  /* Rowid components */
  const u8 *aBlob; int n;         /* Record to decode */
  u8 *a = 0;
  Fts5Buffer s;                   /* Build up text to return here */
  int rc = SQLITE_OK;             /* Return code */
  int nSpace = 0;

  assert( nArg==2 );
  memset(&s, 0, sizeof(Fts5Buffer));
  iRowid = sqlite3_value_int64(apVal[0]);
  n = sqlite3_value_bytes(apVal[1]);
  aBlob = sqlite3_value_blob(apVal[1]);

  nSpace = n + FTS5_DATA_ZERO_PADDING;
  a = (u8*)sqlite3Fts5MallocZero(&rc, nSpace);
  if( a==0 ) goto decode_out;
  memcpy(a, aBlob, n);
  fts5DecodeRowid(iRowid, &iIdx, &iSegid, &iHeight, &iPgno);

  fts5DebugRowid(&rc, &s, iRowid);
  if( iHeight==FTS5_SEGMENT_MAX_HEIGHT ){
    Fts5Data dlidx;
    Fts5DlidxIter iter;

    dlidx.p = a;

  const char *zArg;
  if( nArg==0 ){
    sqlite3_result_error(pCtx, "should be: fts5_rowid(subject, ....)", -1);
  }else{
    zArg = (const char*)sqlite3_value_text(apVal[0]);
    if( 0==sqlite3_stricmp(zArg, "segment") ){
      i64 iRowid;
      int idx, segid, height, pgno;
      if( nArg!=5 ){
        sqlite3_result_error(pCtx, 
            "should be: fts5_rowid('segment', idx, segid, height, pgno))", -1
        );
      }else{
        idx = sqlite3_value_int(apVal[1]);
        segid = sqlite3_value_int(apVal[2]);
        height = sqlite3_value_int(apVal[3]);
        pgno = sqlite3_value_int(apVal[4]);
        iRowid = FTS5_SEGMENT_ROWID(idx, segid, height, pgno);
        sqlite3_result_int64(pCtx, iRowid);
      }

    }else if( 0==sqlite3_stricmp(zArg, "start-of-index") ){
      i64 iRowid;
      int idx;
      if( nArg!=2 ){
        sqlite3_result_error(pCtx, 
            "should be: fts5_rowid('start-of-index', idx)", -1
        );
      }else{
        idx = sqlite3_value_int(apVal[1]);
        iRowid = FTS5_SEGMENT_ROWID(idx, 1, 0, 0);
        sqlite3_result_int64(pCtx, iRowid);
      }

    }else {
      sqlite3_result_error(pCtx, 
        "first arg to fts5_rowid() must be 'segment' "
        "or 'start-of-index'"
        , -1
      );
    }

      );
    }
    if( rc==SQLITE_OK ){
      rc = sqlite3Fts5CreateTable(
          pConfig, "config", "k PRIMARY KEY, v", 1, pzErr
      );
    }



  }

  if( rc ){
    sqlite3Fts5StorageClose(p);
    *pp = 0;
  }
  return rc;

  );

  /* Reinitialize the %_data table. This call creates the initial structure
  ** and averages records.  */
  if( rc==SQLITE_OK ){
    rc = sqlite3Fts5IndexReinit(p->pIndex);
  }



  return rc;
}

int sqlite3Fts5StorageRebuild(Fts5Storage *p){
  Fts5Buffer buf = {0,0,0};
  Fts5Config *pConfig = p->pConfig;
  sqlite3_stmt *pScan = 0;

int sqlite3Fts5StorageRollback(Fts5Storage *p){
  p->bTotalsValid = 0;
  return sqlite3Fts5IndexRollback(p->pIndex);
}

int sqlite3Fts5StorageConfigValue(
  Fts5Storage *p, 
  const char *z, 
  sqlite3_value *pVal

){
  sqlite3_stmt *pReplace = 0;
  int rc = fts5StorageGetStmt(p, FTS5_STMT_REPLACE_CONFIG, &pReplace, 0);
  if( rc==SQLITE_OK ){
    sqlite3_bind_text(pReplace, 1, z, -1, SQLITE_STATIC);

    sqlite3_bind_value(pReplace, 2, pVal);



    sqlite3_step(pReplace);
    rc = sqlite3_reset(pReplace);
  }
  if( rc==SQLITE_OK ){
    int iNew = p->pConfig->iCookie + 1;
    rc = sqlite3Fts5IndexSetCookie(p->pIndex, iNew);
    if( rc==SQLITE_OK ){
      p->pConfig->iCookie = iNew;
    }
  }
  return rc;
}


#endif /* SQLITE_ENABLE_FTS5 */

  finish_test
  return
}

do_execsql_test 1.1 {
  CREATE VIRTUAL TABLE ft1 USING fts5(x);
  SELECT * FROM ft1_config;
} {}

do_execsql_test 1.2 {
  INSERT INTO ft1(ft1, rank) VALUES('pgsz', 32);
  SELECT * FROM ft1_config;
} {pgsz 32}

do_execsql_test 1.3 {
  INSERT INTO ft1(ft1, rank) VALUES('pgsz', 64);
  SELECT * FROM ft1_config;
} {pgsz 64}

#--------------------------------------------------------------------------
# Test the logic for parsing the rank() function definition.
#
foreach {tn defn} {
  1 "fname()"
  2 "fname(1)"

db_save

do_execsql_test 1.2 { INSERT INTO t1(t1) VALUES('integrity-check') }
set segid [lindex [fts5_level_segids t1] 0]

do_test 1.3 {
  execsql {
    DELETE FROM t1_data WHERE rowid = fts5_rowid('segment', 0, $segid, 0, 4);
  }
  catchsql { INSERT INTO t1(t1) VALUES('integrity-check') }
} {1 {database disk image is malformed}}

do_test 1.4 {
  db_restore_and_reopen
  execsql {
    UPDATE t1_data set block = X'00000000' || substr(block, 5) WHERE
    rowid = fts5_rowid('segment', 0, $segid, 0, 4);
  }
  catchsql { INSERT INTO t1(t1) VALUES('integrity-check') }
} {1 {database disk image is malformed}}

db_restore_and_reopen
#db eval {SELECT rowid, fts5_decode(rowid, block) aS r FROM t1_data} {puts $r}

  INSERT INTO x3(x3, rank) VALUES('pgsz', 32);
  WITH ii(i) AS (SELECT 1 UNION ALL SELECT i+1 FROM ii WHERE i<1000) 
  INSERT INTO x3 
  SELECT ($doc || CASE WHEN (i%50)==0 THEN 'X' ELSE 'Y' END) FROM ii;
}

foreach {tn hdr} {
  1 "\00\00\00\00"
  2 "\FF\FF\FF\FF"
} {
  set tn2 0
  set nCorrupt 0
  foreach rowid [db eval {SELECT rowid FROM x3_data WHERE rowid>10}] {
    if {$rowid & $mask} continue
    incr tn2
    do_test 3.$tn.$tn2 {

  11 {a AND "abc}                  {unterminated string}

  12 {NEAR(a b, xyz)}              {expected integer, got "xyz"}
  13 {NEAR(a b, // )}              {expected integer, got "//"}
} {
  do_catchsql_test 3.$tn {SELECT fts5_expr($expr, 'name', 'addr')} [list 1 $err]
}











finish_test

#   2: INSERT statement
#   3: DELETE statement
#   4: MATCH expressions
#
#

faultsim_save_and_close
do_faultsim_test 1 -prep {
  faultsim_restore_and_reopen
} -body {
  execsql { CREATE VIRTUAL TABLE t1 USING fts5(a, b, prefix='1, 2, 3') }
} -test {
  faultsim_test_result {0 {}} 
}

reset_db
do_execsql_test 2.0 {
  CREATE VIRTUAL TABLE t1 USING fts5(a, b, prefix='1, 2, 3');
}
faultsim_save_and_close

do_faultsim_test 6.2 -faults oom-t* -body {
  db eval { SELECT previc(x3) FROM x3 WHERE x3 MATCH 'a' }
} -test {
  faultsim_test_result {0 {0 2 7}} {1 SQLITE_NOMEM}
}

}

#-------------------------------------------------------------------------
# OOM error when querying for a phrase with many tokens.
#
reset_db
do_execsql_test 7.0 {
  CREATE VIRTUAL TABLE tt USING fts5(x, y);
  INSERT INTO tt VALUES('f b g b c b', 'f a d c c b');  -- 1

}

do_faultsim_test 9.1 -faults oom-* -body {
  db eval { SELECT rowid FROM tt WHERE tt MATCH 'a NOT x' }
} -test {
  faultsim_test_result {0 {50 100 150 200}} {1 SQLITE_NOMEM}
}

































finish_test

#
# This file containst tests focused on prefix indexes.
#

source [file join [file dirname [info script]] fts5_common.tcl]
set testprefix fts5prefix













#-------------------------------------------------------------------------
# Check that prefix indexes really do index n-character prefixes, not 
# n-byte prefixes. Use the ascii tokenizer so as not to be confused by
# diacritic removal.
#
do_execsql_test 1.0 { 
  CREATE VIRTUAL TABLE t1 USING fts5(x, tokenize = ascii, prefix = 2) 
}

do_test 1.2 {
  foreach {rowid string} {
    1 "\xCA\xCB\xCC\xCD"
    2 "\u1234\u5678\u4321\u8765"
  } {
    execsql { INSERT INTO t1(rowid, x) VALUES($rowid, $string) }
  }
} {}

do_execsql_test 1.1.2 {
  INSERT INTO t1(t1) VALUES('integrity-check');
}

#db eval { select fts5_decode(id, block) AS d FROM t1_data; } { puts $d }

foreach o {1 2} {
  if {$o==2} breakpoint
  foreach {tn q res} {
    1 "SELECT rowid FROM t1 WHERE t1 MATCH '\xCA\xCB*'" 1
    2 "SELECT rowid FROM t1 WHERE t1 MATCH '\u1234\u5678*'" 2
  } {
    do_execsql_test 1.$o.$tn $q $res
  }

  execsql {
    DELETE FROM t1_data WHERE 
    rowid>=fts5_rowid('start-of-index', 0) AND 
    rowid<fts5_rowid('start-of-index', 1);
  }
}


finish_test

do_catchsql_test 1.1 {
  SELECT fts5_rowid()
} {1 {should be: fts5_rowid(subject, ....)}}

do_catchsql_test 1.2 {
  SELECT fts5_rowid('segment')
} {1 {should be: fts5_rowid('segment', idx, segid, height, pgno))}}

do_execsql_test 1.3 {
  SELECT fts5_rowid('segment', 1, 1, 1, 1)
} {4503670494330881}

do_catchsql_test 1.4 {
  SELECT fts5_rowid('start-of-index');
} {1 {should be: fts5_rowid('start-of-index', idx)}}

do_execsql_test 1.5 {
  SELECT fts5_rowid('start-of-index', 1);
} {4503668346847232}

do_catchsql_test 1.4 {
  SELECT fts5_rowid('nosucharg');
} {1 {first arg to fts5_rowid() must be 'segment' or 'start-of-index'}} 


#-------------------------------------------------------------------------

  puts stderr "  -fts4        (use fts4 instead of fts5)"
  puts stderr "  -fts5        (use fts5)"
  puts stderr "  -porter      (use porter tokenizer)"
  puts stderr "  -delete      (delete the database file before starting)"
  puts stderr "  -limit N     (load no more than N documents)"
  puts stderr "  -automerge N (set the automerge parameter to N)"
  puts stderr "  -crisismerge N (set the crisismerge parameter to N)"

  exit 1
}

set O(vtab)       fts5
set O(tok)        ""
set O(limit)      0
set O(delete)     0
set O(automerge)  -1
set O(crisismerge)  -1


if {[llength $argv]<2} usage
set nOpt [expr {[llength $argv]-2}]
for {set i 0} {$i < $nOpt} {incr i} {
  set arg [lindex $argv $i]
  switch -- [lindex $argv $i] {
    -fts4 {

      set O(automerge) [lindex $argv $i]
    }

    -crisismerge {
      if { [incr i]>=$nOpt } usage
      set O(crisismerge) [lindex $argv $i]
    }






    default {
      usage
    }
  }
}

set dbfile [lindex $argv end-1]
if {$O(delete)} { file delete -force $dbfile }
sqlite3 db $dbfile
db func loadfile loadfile

db transaction {


  catch {
    db eval "CREATE VIRTUAL TABLE t1 USING $O(vtab) (path, content$O(tok))"
  }
  if {$O(automerge)>=0} {
    if {$O(vtab) == "fts5"} {
      db eval { INSERT INTO t1(t1, rank) VALUES('automerge', $O(automerge)) }
    } else {
      db eval { INSERT INTO t1(t1) VALUES('automerge=' || $O(automerge)) }
    }