SQLite

  /* If the file was opened successfully, read the schema for the new database.
  ** If this fails, or if opening the file failed, then close the file and 
  ** remove the entry from the db->aDb[] array. i.e. put everything back the
  ** way we found it.
  */
  if( rc==SQLITE_OK ){
    db->init.iDb = 0;

    if( !IsReuseSchema(db) ){
      db->mDbFlags &= ~(DBFLAG_SchemaKnownOk);
      sqlite3BtreeEnterAll(db);
      rc = sqlite3Init(db, &zErrDyn);
      sqlite3BtreeLeaveAll(db);
      assert( zErrDyn==0 || rc!=SQLITE_OK );
    }
  }
#ifdef SQLITE_USER_AUTHENTICATION

      Module *pMod = (Module*)sqlite3HashFind(&db->aModule, zName);
      if( pMod==0 && sqlite3_strnicmp(zName, "pragma_", 7)==0 ){
        pMod = sqlite3PragmaVtabRegister(db, zName);
      }
      if( pMod ){
        sqlite3SchemaLoad(db, 0);
        if( sqlite3VtabEponymousTableInit(pParse, pMod) ){
          Table *pEpoTab = pMod->pEpoTab;
          assert( IsReuseSchema(db) || pEpoTab->pSchema==db->aDb[0].pSchema );
          pEpoTab->pSchema = db->aDb[0].pSchema;  /* For SHARED_SCHEMA mode */
          return pEpoTab;
        }
      }
    }
#endif
    if( flags & LOCATE_NOERR ) return 0;
    pParse->checkSchema = 1;
  }else if( IsVirtual(p) && pParse->disableVtab ){

** When this function is called, the database connection Db must be
** using a schema-pool (Db.pSPool!=0) and must currently have Db.pSchema
** set to point to a populated schema object checked out from the 
** schema-pool. It is also assumed that the STATIC_MASTER mutex is held.
** This function returns the Schema object to the schema-pool and sets
** Db.pSchema to point to the schema-pool's static, empty, Schema object.
*/
static void schemaRelease(sqlite3 *db, Db *pDb){
  Schema *pRelease = pDb->pSchema;
  SchemaPool *pSPool = pDb->pSPool;

  pDb->pSchema = &pSPool->sSchema;

  assert( pDb->pSPool && pRelease );
  assert( pRelease->schemaFlags & DB_SchemaLoaded );
  assert( (pDb->pSchema->schemaFlags & DB_SchemaLoaded)==0 );
  assert( sqlite3_mutex_held(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER)) );

  /* If the DBFLAG_FreeSchema flag is set and the database connection holds
  ** at least one other copy of the schema being released, delete it instead
  ** of returning it to the schema-pool.  */
  if( db->mDbFlags & DBFLAG_FreeSchema ){
    int i;
    for(i=0; i<db->nDb; i++){
      Db *p = &db->aDb[i];
      if( p!=pDb && p->pSchema!=&pSPool->sSchema && pDb->pSPool==p->pSPool ){
        schemaDelete(pRelease);
        return;
      }
    }
  }

  pRelease->pNext = pDb->pSPool->pSchema;
  pDb->pSPool->pSchema = pRelease;
}

/*
** The schema for database iDb of database handle db, which was opened
** with SQLITE_OPEN_SHARED_SCHEMA, has just been parsed. This function either
** finds a matching SchemaPool object on the global list (schemaPoolList) or
** else allocates a new one and sets the Db.pSPool variable accordingly.

      for(p=pDb->pVTable; p; p=pNext){
        pNext = p->pNext;
        sqlite3VtabUnlock(p);
      }
      pDb->pVTable = 0;
      sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
      if( DbHasProperty(db, iDb, DB_SchemaLoaded) ){
        schemaRelease(db, pDb);
      }
      if( bNew ){
        Schema *pNew = sqlite3SchemaGet(db, 0);
        if( pNew==0 ){
          rc = SQLITE_NOMEM;
        }else{
          pDb->pSchema = pNew;

  int i;
  assert_schema_state_ok(db);
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  for(i=0; i<db->nDb; i++){
    if( i!=1 ){
      Db *pDb = &db->aDb[i];
      if( pDb->pSPool && DbHasProperty(db,i,DB_SchemaLoaded) ){
        schemaRelease(db, pDb);
      }
    }
  }
  db->flags &= ~DBFLAG_FreeSchema;
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
}

/*
** Release any sharable schema held by connection iDb of database handle
** db. Db.pSchema is left pointing to the static, empty, Schema object
** owned by the schema-pool.
*/
void sqlite3SchemaRelease(sqlite3 *db, int iDb){
  Db *pDb = &db->aDb[iDb];
  assert( iDb!=1 );
  assert_schema_state_ok(db);
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  if( pDb->pSPool && DbHasProperty(db, iDb, DB_SchemaLoaded) ){
    schemaRelease(db, pDb);
  }
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
}

/*
** In most cases, this function finds and returns the schema associated 
** with BTree handle pBt, creating a new one if necessary. However, if

** Otherwise, the schema is loaded. An error code is returned.
*/
int sqlite3ReadSchema(Parse *pParse){
  int rc = SQLITE_OK;
  sqlite3 *db = pParse->db;
  assert( sqlite3_mutex_held(db->mutex) );
  if( !db->init.busy ){
    db->mDbFlags |= DBFLAG_FreeSchema;      /* For sharable-schema mode */
    rc = sqlite3Init(db, &pParse->zErrMsg);
    if( rc!=SQLITE_OK ){
      pParse->rc = rc;
      pParse->nErr++;
    }else if( db->noSharedCache && !IsReuseSchema(db) ){
      db->mDbFlags |= DBFLAG_SchemaKnownOk;
    }

** Allowed values for sqlite3.mDbFlags
*/
#define DBFLAG_SchemaChange   0x0001  /* Uncommitted Hash table changes */
#define DBFLAG_PreferBuiltin  0x0002  /* Preference to built-in funcs */
#define DBFLAG_Vacuum         0x0004  /* Currently in a VACUUM */
#define DBFLAG_SchemaKnownOk  0x0008  /* Schema is known to be valid */

#define DBFLAG_SchemaInuse    0x0010  /* Do not release sharable schemas */
#define DBFLAG_FreeSchema     0x0020  /* Free extra shared schemas on release */

/*
** Bits of the sqlite3.dbOptFlags field that are used by the
** sqlite3_test_control(SQLITE_TESTCTRL_OPTIMIZATIONS,...) interface to
** selectively disable various optimizations.
*/
#define SQLITE_QueryFlattener 0x0001   /* Query flattening */

  sqlite3_table_column_metadata db2 main bbb b
} {{} BINARY 0 0 0}

do_execsql_test -db db2 5.2.3 {
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool ORDER BY 1;
} {nref=6 nschema=1}

breakpoint
do_execsql_test -db db2 5.2.4 {
  PRAGMA integrity_check;
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool ORDER BY 1;
} {ok nref=6 nschema=1}

finish_test

  set N [lindex [sqlite3_db_status db1 SCHEMA_USED 0] 1]
  expr $N==$N
} 1

sqlite3 db2 test.db -shared-schema 1
do_test 3.2 {
  execsql { SELECT * FROM x1 } db2

  set N2 [lindex [sqlite3_db_status db2 SCHEMA_USED 0] 1]
  expr $N2>($N/2) && $N2<($N/2)+400
} 1

sqlite3 db3 test.db -shared-schema 1
sqlite3 db4 test.db -shared-schema 1
do_test 3.3 {
  execsql { SELECT * FROM x1 } db3
  execsql { SELECT * FROM x1 } db4
  set N4 [lindex [sqlite3_db_status db2 SCHEMA_USED 0] 1]
  set M [expr 2*($N-$N2)]
  expr {$N4 == (($M / 4) + $N-$M)}
} 1

catch { db1 close }
catch { db2 close }
catch { db3 close }
catch { db4 close }

#-------------------------------------------------------------------------
# Test the REINDEX command.
reset_db
do_execsql_test 4.1.0 {
  CREATE TABLE x1(a, b, c);
  CREATE INDEX x1a ON x1(a);
  CREATE INDEX x1b ON x1(b);
  CREATE INDEX x1c ON x1(c);
}
db close
sqlite3 db test.db -shared-schema 1

do_execsql_test 4.1.1 {
  REINDEX x1;
  REINDEX x1a;
  REINDEX x1b;
  REINDEX x1c;
  REINDEX;
}

do_test 4.1.2 {
  for {set i 1} {$i < 5} {incr i} {
    forcedelete test.db${i} test.db${i}-wal test.db${i}-journal
    forcecopy test.db test.db${i}
    execsql "ATTACH 'test.db${i}' AS db${i}"
  }
  register_schemapool_module db
  set {} {}
  execsql { SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool }
} {nref=5 nschema=1}

do_execsql_test 4.1.3 {
  REINDEX x1;
  REINDEX x1a;
  REINDEX x1b;
  REINDEX x1c;
  REINDEX db1.x1a;
  REINDEX db2.x1b;
  REINDEX db3.x1c;
  REINDEX;
}

do_execsql_test 4.1.4 {
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool;
} {nref=5 nschema=1}

finish_test