BtLock *pLock;

  /* If this database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** Return true immediately.
  */
  if( (pBtree->sharable==0)
   || (eLockType==READ_LOCK && (pBtree->db->flags & SQLITE_ReadUncommit))
  ){
    return 1;
  }

  /* If the client is reading  or writing an index and the schema is
  ** not loaded, then it is too difficult to actually check to see if
  ** the correct locks are held.  So do not bother - just return true.

**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree *pBtree, Pgno iRoot){
  BtCursor *p;
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    if( p->pgnoRoot==iRoot 
     && p->pBtree!=pBtree
     && 0==(p->pBtree->db->flags & SQLITE_ReadUncommit)
    ){
      return 1;
    }
  }
  return 0;
}
#endif    /* #ifdef SQLITE_DEBUG */

static int querySharedCacheTableLock(Btree *p, Pgno iTab, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pIter;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( p->db!=0 );
  assert( !(p->db->flags&SQLITE_ReadUncommit)||eLock==WRITE_LOCK||iTab==1 );
  
  /* If requesting a write-lock, then the Btree must have an open write
  ** transaction on this file. And, obviously, for this to be so there 
  ** must be an open write transaction on the file itself.
  */
  assert( eLock==READ_LOCK || (p==pBt->pWriter && p->inTrans==TRANS_WRITE) );
  assert( eLock==READ_LOCK || pBt->inTransaction==TRANS_WRITE );

  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( p->db!=0 );

  /* A connection with the read-uncommitted flag set will never try to
  ** obtain a read-lock using this function. The only read-lock obtained
  ** by a connection in read-uncommitted mode is on the sqlite_master 
  ** table, and that lock is obtained in BtreeBeginTrans().  */
  assert( 0==(p->db->flags&SQLITE_ReadUncommit) || eLock==WRITE_LOCK );

  /* This function should only be called on a sharable b-tree after it 
  ** has been determined that no other b-tree holds a conflicting lock.  */
  assert( p->sharable );
  assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );

  /* First search the list for an existing lock on this table. */

      pBt->usableSize = usableSize;
      pBt->pageSize = pageSize;
      freeTempSpace(pBt);
      rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize,
                                   pageSize-usableSize);
      return rc;
    }
    if( (pBt->db->flags & SQLITE_WriteSchema)==0 && nPage>nPageFile ){
      rc = SQLITE_CORRUPT_BKPT;
      goto page1_init_failed;
    }
    /* EVIDENCE-OF: R-28312-64704 However, the usable size is not allowed to
    ** be less than 480. In other words, if the page size is 512, then the
    ** reserved space size cannot exceed 32. */
    if( usableSize<480 ){

        u32 mask;    /* Mask of the bit in sqlite3.flags to set/clear */
      } aFlagOp[] = {
        { SQLITE_DBCONFIG_ENABLE_FKEY,           SQLITE_ForeignKeys    },
        { SQLITE_DBCONFIG_ENABLE_TRIGGER,        SQLITE_EnableTrigger  },
        { SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER, SQLITE_Fts3Tokenizer  },
        { SQLITE_DBCONFIG_ENABLE_LOAD_EXTENSION, SQLITE_LoadExtension  },
        { SQLITE_DBCONFIG_NO_CKPT_ON_CLOSE,      SQLITE_NoCkptOnClose  },
        { SQLITE_DBCONFIG_ENABLE_QPSG,           SQLITE_EnableQPSG     },
      };
      unsigned int i;
      rc = SQLITE_ERROR; /* IMP: R-42790-23372 */
      for(i=0; i<ArraySize(aFlagOp); i++){
        if( aFlagOp[i].op==op ){
          int onoff = va_arg(ap, int);
          int *pRes = va_arg(ap, int*);

#endif
#if defined(SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
                 | SQLITE_CellSizeCk
#endif
#if defined(SQLITE_ENABLE_FTS3_TOKENIZER)
                 | SQLITE_Fts3Tokenizer
#endif
#if defined(SQLITE_ENABLE_QPSG)
                 | SQLITE_EnableQPSG
#endif
      ;
  sqlite3HashInit(&db->aCollSeq);
#ifndef SQLITE_OMIT_VIRTUALTABLE
  sqlite3HashInit(&db->aModule);
#endif

  /* Add the default collation sequence BINARY. BINARY works for both UTF-8

  /* iArg:      */ 0 },
#endif
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
 {/* zName:     */ "read_uncommitted",
  /* ePragTyp:  */ PragTyp_FLAG,
  /* ePragFlg:  */ PragFlg_Result0|PragFlg_NoColumns1,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ SQLITE_ReadUncommit },
 {/* zName:     */ "recursive_triggers",
  /* ePragTyp:  */ PragTyp_FLAG,
  /* ePragFlg:  */ PragFlg_Result0|PragFlg_NoColumns1,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ SQLITE_RecTriggers },
#endif
#if defined(SQLITE_HAS_CODEC)

  /* iArg:      */ 0 },
#endif
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
 {/* zName:     */ "writable_schema",
  /* ePragTyp:  */ PragTyp_FLAG,
  /* ePragFlg:  */ PragFlg_Result0|PragFlg_NoColumns1,
  /* ColNames:  */ 0, 0,
  /* iArg:      */ SQLITE_WriteSchema },
#endif
};
/* Number of pragmas: 60 on by default, 74 total. */

*/
static void corruptSchema(
  InitData *pData,     /* Initialization context */
  const char *zObj,    /* Object being parsed at the point of error */
  const char *zExtra   /* Error information */
){
  sqlite3 *db = pData->db;
  if( !db->mallocFailed && (db->flags & SQLITE_WriteSchema)==0 ){
    char *z;
    if( zObj==0 ) zObj = "?";
    z = sqlite3MPrintf(db, "malformed database schema (%s)", zObj);
    if( zExtra ) z = sqlite3MPrintf(db, "%z - %s", z, zExtra);
    sqlite3DbFree(db, *pData->pzErrMsg);
    *pData->pzErrMsg = z;
  }

    }
#endif
  }
  if( db->mallocFailed ){
    rc = SQLITE_NOMEM_BKPT;
    sqlite3ResetAllSchemasOfConnection(db);
  }
  if( rc==SQLITE_OK || (db->flags&SQLITE_WriteSchema)){
    /* Black magic: If the SQLITE_WriteSchema flag is set, then consider
    ** the schema loaded, even if errors occurred. In this situation the 
    ** current sqlite3_prepare() operation will fail, but the following one
    ** will attempt to compile the supplied statement against whatever subset
    ** of the schema was loaded before the error occurred. The primary
    ** purpose of this is to allow access to the sqlite_master table
    ** even when its contents have been corrupted.
    */

    Btree *pBt = db->aDb[i].pBt;
    if( pBt ){
      assert( sqlite3BtreeHoldsMutex(pBt) );
      rc = sqlite3BtreeSchemaLocked(pBt);
      if( rc ){
        const char *zDb = db->aDb[i].zDbSName;
        sqlite3ErrorWithMsg(db, rc, "database schema is locked: %s", zDb);
        testcase( db->flags & SQLITE_ReadUncommit );
        goto end_prepare;
      }
    }
  }

  sqlite3VtabUnlockList(db);

** override this behaviour. The first parameter passed to this operation
** is an integer - non-zero to disable checkpoints-on-close, or zero (the
** default) to enable them. The second parameter is a pointer to an integer
** into which is written 0 or 1 to indicate whether checkpoints-on-close
** have been disabled - 0 if they are not disabled, 1 if they are.
** </dd>
**
** <dt>SQLITE_DBCONFIG_ENABLE_QPSG</dt>
** <dd>The SQLITE_DBCONFIG_ENABLE_QPSG option activates or deactivates
** the [query planner stability guarantee] (QPSG).  When the QPSG is active,
** a single SQL query statement will always use the same algorithm regardless
** of values of [bound parameters].  The QPSG disables some query optimizations
** that look at the values of bound parameters, which can make some queries
** slower.  But the QPSG has the advantage of more predictable behavior.  With
** the QPSG active, SQLite will always use the same query plan in the field as
** was used during testing in the lab.
** </dd>
**
** </dl>
*/
#define SQLITE_DBCONFIG_MAINDBNAME            1000 /* const char* */
#define SQLITE_DBCONFIG_LOOKASIDE             1001 /* void* int int */
#define SQLITE_DBCONFIG_ENABLE_FKEY           1002 /* int int* */
#define SQLITE_DBCONFIG_ENABLE_TRIGGER        1003 /* int int* */
#define SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER 1004 /* int int* */
#define SQLITE_DBCONFIG_ENABLE_LOAD_EXTENSION 1005 /* int int* */
#define SQLITE_DBCONFIG_NO_CKPT_ON_CLOSE      1006 /* int int* */
#define SQLITE_DBCONFIG_ENABLE_QPSG           1007 /* int int* */


/*
** CAPI3REF: Enable Or Disable Extended Result Codes
** METHOD: sqlite3
**
** ^The sqlite3_extended_result_codes() routine enables or disables the

** Possible values for the sqlite3.flags.
**
** Value constraints (enforced via assert()):
**      SQLITE_FullFSync     == PAGER_FULLFSYNC
**      SQLITE_CkptFullFSync == PAGER_CKPT_FULLFSYNC
**      SQLITE_CacheSpill    == PAGER_CACHE_SPILL
*/
#define SQLITE_WriteSchema    0x00000001  /* OK to update SQLITE_MASTER */
#define SQLITE_LegacyFileFmt  0x00000002  /* Create new databases in format 1 */
#define SQLITE_FullColNames   0x00000004  /* Show full column names on SELECT */
#define SQLITE_FullFSync      0x00000008  /* Use full fsync on the backend */
#define SQLITE_CkptFullFSync  0x00000010  /* Use full fsync for checkpoint */
#define SQLITE_CacheSpill     0x00000020  /* OK to spill pager cache */
#define SQLITE_ShortColNames  0x00000040  /* Show short columns names */
#define SQLITE_CountRows      0x00000080  /* Count rows changed by INSERT, */
                                          /*   DELETE, or UPDATE and return */
                                          /*   the count using a callback. */
#define SQLITE_NullCallback   0x00000100  /* Invoke the callback once if the */
                                          /*   result set is empty */




#define SQLITE_IgnoreChecks   0x00000200  /* Do not enforce check constraints */
#define SQLITE_ReadUncommit   0x00000400  /* READ UNCOMMITTED in shared-cache */

#define SQLITE_NoCkptOnClose  0x00000800  /* No checkpoint on close()/DETACH */
#define SQLITE_ReverseOrder   0x00001000  /* Reverse unordered SELECTs */
#define SQLITE_RecTriggers    0x00002000  /* Enable recursive triggers */
#define SQLITE_ForeignKeys    0x00004000  /* Enforce foreign key constraints  */
#define SQLITE_AutoIndex      0x00008000  /* Enable automatic indexes */

#define SQLITE_LoadExtension  0x00010000  /* Enable load_extension */

#define SQLITE_EnableTrigger  0x00020000  /* True to enable triggers */
#define SQLITE_DeferFKs       0x00040000  /* Defer all FK constraints */
#define SQLITE_QueryOnly      0x00080000  /* Disable database changes */
#define SQLITE_CellSizeCk     0x00100000  /* Check btree cell sizes on load */
#define SQLITE_Fts3Tokenizer  0x00200000  /* Enable fts3_tokenizer(2) */
#define SQLITE_EnableQPSG     0x00400000  /* Query Planner Stability Guarantee */
/* The next four values are not used by PRAGMAs or by sqlite3_dbconfig() and
** could be factored out into a separate bit vector of the sqlite3 object. */
#define SQLITE_InternChanges  0x00800000  /* Uncommitted Hash table changes */
#define SQLITE_LoadExtFunc    0x01000000  /* Enable load_extension() SQL func */
#define SQLITE_PreferBuiltin  0x02000000  /* Preference to built-in funcs */
#define SQLITE_Vacuum         0x04000000  /* Currently in a VACUUM */
/* Flags used only if debugging */
#ifdef SQLITE_DEBUG
#define SQLITE_SqlTrace       0x08000000  /* Debug print SQL as it executes */
#define SQLITE_VdbeListing    0x10000000  /* Debug listings of VDBE programs */
#define SQLITE_VdbeTrace      0x20000000  /* True to trace VDBE execution */
#define SQLITE_VdbeAddopTrace 0x40000000  /* Trace sqlite3VdbeAddOp() calls */
#define SQLITE_VdbeEQP        0x80000000  /* Debug EXPLAIN QUERY PLAN */
#endif


/*
** Bits of the sqlite3.dbOptFlags field that are used by the
** sqlite3_test_control(SQLITE_TESTCTRL_OPTIMIZATIONS,...) interface to
** selectively disable various optimizations.
*/

    int eVal;
  } aSetting[] = {
    { "FKEY",            SQLITE_DBCONFIG_ENABLE_FKEY },
    { "TRIGGER",         SQLITE_DBCONFIG_ENABLE_TRIGGER },
    { "FTS3_TOKENIZER",  SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER },
    { "LOAD_EXTENSION",  SQLITE_DBCONFIG_ENABLE_LOAD_EXTENSION },
    { "NO_CKPT_ON_CLOSE",SQLITE_DBCONFIG_NO_CKPT_ON_CLOSE },
    { "QPSG",            SQLITE_DBCONFIG_ENABLE_QPSG },
  };
  int i;
  int v;
  const char *zSetting;
  sqlite3 *db;

  if( objc!=4 ){

** P2 contains the root-page of the table to lock.
**
** P4 contains a pointer to the name of the table being locked. This is only
** used to generate an error message if the lock cannot be obtained.
*/
case OP_TableLock: {
  u8 isWriteLock = (u8)pOp->p3;
  if( isWriteLock || 0==(db->flags&SQLITE_ReadUncommit) ){
    int p1 = pOp->p1; 
    assert( p1>=0 && p1<db->nDb );
    assert( DbMaskTest(p->btreeMask, p1) );
    assert( isWriteLock==0 || isWriteLock==1 );
    rc = sqlite3BtreeLockTable(db->aDb[p1].pBt, pOp->p2, isWriteLock);
    if( rc ){
      if( (rc&0xFF)==SQLITE_LOCKED ){

**
** The returned value must be freed by the caller using sqlite3ValueFree().
*/
sqlite3_value *sqlite3VdbeGetBoundValue(Vdbe *v, int iVar, u8 aff){
  assert( iVar>0 );
  if( v ){
    Mem *pMem = &v->aVar[iVar-1];
    assert( (v->db->flags & SQLITE_EnableQPSG)==0 );
    if( 0==(pMem->flags & MEM_Null) ){
      sqlite3_value *pRet = sqlite3ValueNew(v->db);
      if( pRet ){
        sqlite3VdbeMemCopy((Mem *)pRet, pMem);
        sqlite3ValueApplyAffinity(pRet, aff, SQLITE_UTF8);
      }
      return pRet;
    }
  }
  return 0;
}

/*
** Configure SQL variable iVar so that binding a new value to it signals
** to sqlite3_reoptimize() that re-preparing the statement may result
** in a better query plan.
*/
void sqlite3VdbeSetVarmask(Vdbe *v, int iVar){
  assert( iVar>0 );
  assert( (v->db->flags & SQLITE_EnableQPSG)==0 );
  if( iVar>=32 ){
    v->expmask |= 0x80000000;
  }else{
    v->expmask |= ((u32)1 << (iVar-1));
  }
}

  int rc = SQLITE_OK;
  sqlite3_value *pVal = 0;
  sqlite3 *db = pParse->db;

  /* Skip over any TK_COLLATE nodes */
  pExpr = sqlite3ExprSkipCollate(pExpr);

  assert( pExpr==0 || pExpr->op!=TK_REGISTER || pExpr->op2!=TK_VARIABLE );
  if( !pExpr ){
    pVal = valueNew(db, pAlloc);
    if( pVal ){
      sqlite3VdbeMemSetNull((Mem*)pVal);
    }
  }else if( pExpr->op==TK_VARIABLE && (db->flags & SQLITE_EnableQPSG)==0 ){


    Vdbe *v;
    int iBindVar = pExpr->iColumn;
    sqlite3VdbeSetVarmask(pParse->pVdbe, iBindVar);
    if( (v = pParse->pReprepare)!=0 ){
      pVal = valueNew(db, pAlloc);
      if( pVal ){
        rc = sqlite3VdbeMemCopy((Mem*)pVal, &v->aVar[iBindVar-1]);

        sqlite3ValueApplyAffinity(pVal, affinity, ENC(db));

        pVal->db = pParse->db;
      }
    }
  }else{
    rc = valueFromExpr(db, pExpr, ENC(db), affinity, &pVal, pAlloc);
  }

  if( *pnoCase ) return 0;
#endif
  pList = pExpr->x.pList;
  pLeft = pList->a[1].pExpr;

  pRight = sqlite3ExprSkipCollate(pList->a[0].pExpr);
  op = pRight->op;
  if( op==TK_VARIABLE && (db->flags & SQLITE_EnableQPSG)==0 ){
    Vdbe *pReprepare = pParse->pReprepare;
    int iCol = pRight->iColumn;
    pVal = sqlite3VdbeGetBoundValue(pReprepare, iCol, SQLITE_AFF_BLOB);
    if( pVal && sqlite3_value_type(pVal)==SQLITE_TEXT ){
      z = (char *)sqlite3_value_text(pVal);
    }
    sqlite3VdbeSetVarmask(pParse->pVdbe, iCol);

#
do_eqp_test analyze3-1.1.2 {
  SELECT sum(y) FROM t1 WHERE x>200 AND x<300
} {0 0 0 {SEARCH TABLE t1 USING INDEX i1 (x>? AND x<?)}}
do_eqp_test analyze3-1.1.3 {
  SELECT sum(y) FROM t1 WHERE x>0 AND x<1100 
} {0 0 0 {SCAN TABLE t1}}

# 2017-06-26:  Verify that the SQLITE_DBCONFIG_ENABLE_QPSG setting disables
# the use of bound parameters by STAT4
#
db cache flush
unset -nocomplain l
unset -nocomplain u
do_eqp_test analyze3-1.1.3.100 {
  SELECT sum(y) FROM t1 WHERE x>$l AND x<$u
} {0 0 0 {SEARCH TABLE t1 USING INDEX i1 (x>? AND x<?)}}
set l 200
set u 300
do_eqp_test analyze3-1.1.3.101 {
  SELECT sum(y) FROM t1 WHERE x>$l AND x<$u
} {0 0 0 {SEARCH TABLE t1 USING INDEX i1 (x>? AND x<?)}}
set l 0
set u 1100
do_eqp_test analyze3-1.1.3.102 {
  SELECT sum(y) FROM t1 WHERE x>$l AND x<$u
} {0 0 0 {SCAN TABLE t1}}
db cache flush
sqlite3_db_config db ENABLE_QPSG 1
do_eqp_test analyze3-1.1.3.103 {
  SELECT sum(y) FROM t1 WHERE x>$l AND x<$u
} {0 0 0 {SEARCH TABLE t1 USING INDEX i1 (x>? AND x<?)}}
db cache flush
sqlite3_db_config db ENABLE_QPSG 0
do_eqp_test analyze3-1.1.3.104 {
  SELECT sum(y) FROM t1 WHERE x>$l AND x<$u
} {0 0 0 {SCAN TABLE t1}}

do_test analyze3-1.1.4 {
  sf_execsql { SELECT sum(y) FROM t1 WHERE x>200 AND x<300 }
} {199 0 14850}
do_test analyze3-1.1.5 {
  set l [string range "200" 0 end]
  set u [string range "300" 0 end]

# This procedure executes the SQL.  Then it appends to the result the
# "sort" or "nosort" keyword (as in the cksort procedure above) then
# it appends the names of the table and index used.
#
proc queryplan {sql} {
  set ::sqlite_sort_count 0
  db cache flush
  set data [execsql $sql]
  if {$::sqlite_sort_count} {set x sort} {set x nosort}
  lappend data $x
  set eqp [execsql "EXPLAIN QUERY PLAN $sql"]
  # puts eqp=$eqp
  foreach {a b c x} $eqp {
    if {[regexp { TABLE (\w+ AS )?(\w+) USING COVERING INDEX (\w+)\y} \

} {ABC {ABC abc xyz} abc abcd sort t1 *}
do_test like-3.2 {
  set sqlite_like_count
} {12}

# With an index on t1.x and case sensitivity on, optimize completely.
#
do_test like-3.3.100 {
  set sqlite_like_count 0
  execsql {
    PRAGMA case_sensitive_like=on;
    CREATE INDEX i1 ON t1(x);
  }
  queryplan {
    SELECT x FROM t1 WHERE x LIKE 'abc%' ORDER BY 1;
  }
} {abc abcd nosort {} i1}
do_test like-3.3.101 {
  set sqlite_like_count
} 0

# The like optimization works even when the pattern is a bound parameter
#
do_test like-3.3.102 {
  set sqlite_like_count 0
  unset -nocomplain ::likepat
  set ::likepat abc%
  queryplan {
    SELECT x FROM t1 WHERE x LIKE $::likepat ORDER BY 1;
  }
} {abc abcd nosort {} i1}
do_test like-3.3.103 {
  set sqlite_like_count
} 0

# Except, the like optimization does not work for bound parameters if
# the query planner stability guarantee is active.
#
do_test like-3.3.104 {
  set sqlite_like_count 0
  sqlite3_db_config db QPSG 1
  queryplan {
    SELECT x FROM t1 WHERE x LIKE $::likepat ORDER BY 1;
  }
} {abc abcd nosort {} i1}
do_test like-3.3.105 {
  set sqlite_like_count
} 12

# The query planner stability guarantee does not disrupt explicit patterns
#
do_test like-3.3.105 {
  set sqlite_like_count 0
  queryplan {
    SELECT x FROM t1 WHERE x LIKE 'abc%' ORDER BY 1;
  }
} {abc abcd nosort {} i1}
do_test like-3.3.106 {
  set sqlite_like_count
} 0
sqlite3_db_config db QPSG 0

# The LIKE optimization still works when the RHS is a string with no
# wildcard.  Ticket [e090183531fc2747]
#
do_test like-3.4.2 {
  queryplan {
    SELECT x FROM t1 WHERE x LIKE 'a' ORDER BY 1;

  TYPE: FLAG
  ARG:  SQLITE_IgnoreChecks
  IF:   !defined(SQLITE_OMIT_FLAG_PRAGMAS)
  IF:   !defined(SQLITE_OMIT_CHECK)

  NAME: writable_schema
  TYPE: FLAG
  ARG:  SQLITE_WriteSchema
  IF:   !defined(SQLITE_OMIT_FLAG_PRAGMAS)

  NAME: read_uncommitted
  TYPE: FLAG
  ARG:  SQLITE_ReadUncommit
  IF:   !defined(SQLITE_OMIT_FLAG_PRAGMAS)

  NAME: recursive_triggers
  TYPE: FLAG
  ARG:  SQLITE_RecTriggers
  IF:   !defined(SQLITE_OMIT_FLAG_PRAGMAS)