#endif

#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
  /*
  ** If this Btree is a candidate for shared cache, try to find an
  ** existing BtShared object that we can share with
  */
  if( isTempDb==0 && (isMemdb==0 || (vfsFlags&SQLITE_OPEN_URI)!=0) ){
    if( vfsFlags & SQLITE_OPEN_SHAREDCACHE ){
      int nFullPathname = pVfs->mxPathname+1;
      char *zFullPathname = sqlite3Malloc(nFullPathname);
      MUTEX_LOGIC( sqlite3_mutex *mutexShared; )
      p->sharable = 1;
      if( !zFullPathname ){
        sqlite3_free(p);
        return SQLITE_NOMEM;
      }
      if( isMemdb ){
        memcpy(zFullPathname, zFilename, sqlite3Strlen30(zFilename)+1);
      }else{
        rc = sqlite3OsFullPathname(pVfs, zFilename,
                                   nFullPathname, zFullPathname);
        if( rc ){
          sqlite3_free(zFullPathname);
          sqlite3_free(p);
          return rc;
        }
      }
#if SQLITE_THREADSAFE
      mutexOpen = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_OPEN);
      sqlite3_mutex_enter(mutexOpen);
      mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
      sqlite3_mutex_enter(mutexShared);
#endif
      for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt->pNext){
        assert( pBt->nRef>0 );
        if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager, 0))
                 && sqlite3PagerVfs(pBt->pPager)==pVfs ){
          int iDb;
          for(iDb=db->nDb-1; iDb>=0; iDb--){
            Btree *pExisting = db->aDb[iDb].pBt;
            if( pExisting && pExisting->pBt==pBt ){
              sqlite3_mutex_leave(mutexShared);
              sqlite3_mutex_leave(mutexOpen);

  *pnErr = sCheck.nErr;
  if( sCheck.nErr==0 ) sqlite3StrAccumReset(&sCheck.errMsg);
  return sqlite3StrAccumFinish(&sCheck.errMsg);
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

/*
** Return the full pathname of the underlying database file.  Return
** an empty string if the database is in-memory or a TEMP database.
**
** The pager filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
const char *sqlite3BtreeGetFilename(Btree *p){
  assert( p->pBt->pPager!=0 );
  return sqlite3PagerFilename(p->pBt->pPager, 1);
}

/*
** Return the pathname of the journal file for this database. The return
** value of this routine is the same regardless of whether the journal file
** has been created or not.
**

  }else{
    zFile = sqlite3_malloc(nUri+2);
    if( !zFile ) return SQLITE_NOMEM;
    memcpy(zFile, zUri, nUri);
    zFile[nUri] = '\0';
    zFile[nUri+1] = '\0';
    flags &= ~SQLITE_OPEN_URI;
  }

  *ppVfs = sqlite3_vfs_find(zVfs);
  if( *ppVfs==0 ){
    *pzErrMsg = sqlite3_mprintf("no such vfs: %s", zVfs);
    rc = SQLITE_ERROR;
  }

  /* Set the output variable to NULL in case an error occurs. */
  *ppPager = 0;

#ifndef SQLITE_OMIT_MEMORYDB
  if( flags & PAGER_MEMORY ){
    memDb = 1;
    if( zFilename && zFilename[0] ){
      zPathname = sqlite3DbStrDup(0, zFilename);
      if( zPathname==0  ) return SQLITE_NOMEM;
      nPathname = sqlite3Strlen30(zPathname);
      zFilename = 0;
    }
  }
#endif

  /* Compute and store the full pathname in an allocated buffer pointed
  ** to by zPathname, length nPathname. Or, if this is a temporary file,
  ** leave both nPathname and zPathname set to 0.
  */

  }

  return rc;
}

/*
** Return the full pathname of the database file.
**
** Except, if the pager is in-memory only, then return an empty string if
** nullIfMemDb is true.  This routine is called with nullIfMemDb==1 when
** used to report the filename to the user, for compatibility with legacy
** behavior.  But when the Btree needs to know the filename for matching to
** shared cache, it uses nullIfMemDb==0 so that in-memory databases can
** participate in shared-cache.
*/
const char *sqlite3PagerFilename(Pager *pPager, int nullIfMemDb){
  return (nullIfMemDb && pPager->memDb) ? "" : pPager->zFilename;
}

/*
** Return the VFS structure for the pager.
*/
const sqlite3_vfs *sqlite3PagerVfs(Pager *pPager){
  return pPager->pVfs;

  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */
u8 sqlite3PagerIsreadonly(Pager*);
int sqlite3PagerRefcount(Pager*);
int sqlite3PagerMemUsed(Pager*);
const char *sqlite3PagerFilename(Pager*, int);
const sqlite3_vfs *sqlite3PagerVfs(Pager*);
sqlite3_file *sqlite3PagerFile(Pager*);
const char *sqlite3PagerJournalname(Pager*);
int sqlite3PagerNosync(Pager*);
void *sqlite3PagerTempSpace(Pager*);
int sqlite3PagerIsMemdb(Pager*);
void sqlite3PagerCacheStat(Pager *, int, int, int *);

  Tcl_Obj *CONST objv[]
){
#ifndef SQLITE_OMIT_SHARED_CACHE
  extern BtShared *sqlite3SharedCacheList;
  BtShared *pBt;
  Tcl_Obj *pRet = Tcl_NewObj();
  for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt->pNext){
    const char *zFile = sqlite3PagerFilename(pBt->pPager, 1);
    Tcl_ListObjAppendElement(interp, pRet, Tcl_NewStringObj(zFile, -1));
    Tcl_ListObjAppendElement(interp, pRet, Tcl_NewIntObj(pBt->nRef));
  }
  Tcl_SetObjResult(interp, pRet);
#endif
  return TCL_OK;
}

  pBt = db->aDb[pOp->p1].pBt;
  pPager = sqlite3BtreePager(pBt);
  eOld = sqlite3PagerGetJournalMode(pPager);
  if( eNew==PAGER_JOURNALMODE_QUERY ) eNew = eOld;
  if( !sqlite3PagerOkToChangeJournalMode(pPager) ) eNew = eOld;

#ifndef SQLITE_OMIT_WAL
  zFilename = sqlite3PagerFilename(pPager, 1);

  /* Do not allow a transition to journal_mode=WAL for a database
  ** in temporary storage or if the VFS does not support shared memory 
  */
  if( eNew==PAGER_JOURNALMODE_WAL
   && (sqlite3Strlen30(zFilename)==0           /* Temp file */
       || !sqlite3PagerWalSupported(pPager))   /* No shared-memory support */

} {1 2 6 8 9 12 1 2 5 11 12 14 1 2 4}
do_test shared-$av-15.2 {
  execsql { DROP TABLE t1 } db2
} {}
db close
db2 close

# Shared cache on a :memory: database.  This only works for URI filenames.
#
do_test shared-$av-16.1 {
  sqlite3 db1 file::memory: -uri 1
  sqlite3 db2 file::memory: -uri 1
  db1 eval {
    CREATE TABLE t1(x); INSERT INTO t1 VALUES(1),(2),(3);
  }
  db2 eval {
    SELECT x FROM t1 ORDER BY x;
  }
} {1 2 3}
do_test shared-$av-16.2 {
  db2 eval {
    INSERT INTO t1 VALUES(99);
    DELETE FROM t1 WHERE x=2;
  }
  db1 eval {
    SELECT x FROM t1 ORDER BY x;
  }
} {1 3 99}

# Verify that there is no cache sharing ordinary (non-URI) filenames are
# used.
#
do_test shared-$av-16.3 {
  db1 close
  db2 close
  sqlite3 db1 :memory:
  sqlite3 db2 :memory:
  db1 eval {
    CREATE TABLE t1(x); INSERT INTO t1 VALUES(4),(5),(6);
  }
  catchsql {
    SELECT * FROM t1;
  } db2
} {1 {no such table: t1}}
db1 close
db2 close

}  ;# end of autovacuum on/off loop

sqlite3_enable_shared_cache $::enable_shared_cache
finish_test