SQLite

      && DbHasProperty(db, iDb, DB_SchemaLoaded)==0 
      && (db->init.busy==0 || (iDb!=1 && db->init.iDb==1))
  ){
    struct sqlite3InitInfo sv = db->init;
    memset(&db->init, 0, sizeof(struct sqlite3InitInfo));
    rc = sqlite3InitOne(db, iDb, pzErr, 0);
    db->init = sv;
    *pbUnload = (iDb!=1);
    *pbUnload = (rc==SQLITE_OK && (iDb!=1));
  }
  return rc;
}

/*
** Locate the in-memory structure that describes a particular database
** table given the name of that table and (optionally) the name of the

    }
  }

  if( p ) p->nRef++;

  /* If the SchemaPool contains one or more free schemas at the moment, 
  ** delete one of them. */
  if( p->pSchema ){
  if( p && p->pSchema ){
    Schema *pDel = p->pSchema;
    p->pSchema = pDel->pNext;
    schemaDelete(pDel);
  }

  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );

** If the bNew parameter is true, then this function may allocate memory. 
** If the allocation attempt fails, then SQLITE_NOMEM is returned and the
** schema-pool is not disconnected from. Or, if no OOM error occurs, 
** SQLITE_OK is returned.
*/
int sqlite3SchemaDisconnect(sqlite3 *db, int iDb, int bNew){
  int rc = SQLITE_OK;
  if( IsReuseSchema(db) && iDb!=1 ){
  if( IsReuseSchema(db) ){
    Db *pDb = &db->aDb[iDb];
    SchemaPool *pSPool = pDb->pSPool;
    assert_schema_state_ok(db);
    assert( pDb->pSchema );

    if( pSPool==0 ){
      assert( pDb->pVTable==0 );
      if( bNew==0 ){
        schemaDelete(pDb->pSchema);
        pDb->pSchema = 0;
      assert( bNew==0 );
      schemaDelete(pDb->pSchema);
      pDb->pSchema = 0;
      }
    }else{
      VTable *p;
      VTable *pNext;
      for(p=pDb->pVTable; p; p=pNext){
        pNext = p->pNext;
        sqlite3VtabUnlock(p);
      }

/*
** Extract and return a pointer to a schema object from the SchemaPool passed
** as the only argument, if one is available. If one is not available, return
** NULL.
*/
Schema *sqlite3SchemaExtract(SchemaPool *pSPool){
  Schema *pRet = 0;
  if( pSPool ){
    sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
    if( pSPool->pSchema ){
      pRet = pSPool->pSchema;
      pSPool->pSchema = pRet->pNext;
      pRet->pNext = 0;
    }
    sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  if( pSPool->pSchema ){
    pRet = pSPool->pSchema;
    pSPool->pSchema = pRet->pNext;
    pRet->pNext = 0;
  }
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  }
  return pRet;
}

/*
** Return all sharable schemas held by database handle db back to their
** respective schema-pools. Db.pSchema variables are left pointing to
** the static, empty, Schema object owned by each schema-pool.

** 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);
  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
** the database handle was opened with the SQLITE_OPEN_SHARED_SCHEMA flag
** specified, a new, empty, Schema object in memory obtained by 
** sqlite3_malloc() is always returned.
*/
Schema *sqlite3SchemaGet(sqlite3 *db, Btree *pBt){
  Schema *p;
  if( pBt && (db->openFlags & SQLITE_OPEN_SHARED_SCHEMA)==0 ){
    p = (Schema *)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
    p = (Schema*)sqlite3BtreeSchema(pBt, sizeof(Schema), sqlite3SchemaClear);
  }else{
    db->lookaside.bDisable++;
    p = (Schema *)sqlite3DbMallocZero(0, sizeof(Schema));
    p = (Schema*)sqlite3DbMallocZero(db, sizeof(Schema));
    db->lookaside.bDisable--;
  }
  if( !p ){
    sqlite3OomFault(db);
  }else if ( 0==p->file_format ){
    sqlite3HashInit(&p->tblHash);
    sqlite3HashInit(&p->idxHash);
    sqlite3HashInit(&p->trigHash);
    sqlite3HashInit(&p->fkeyHash);
    p->enc = SQLITE_UTF8;
  }
  return p;
}

    if( SQLITE_OK!=rc ){
      if( db->init.orphanTrigger ){
        assert( iDb==1 );
      }else{
        pData->rc = rc;
        if( rc==SQLITE_NOMEM ){
          sqlite3OomFault(db);
        }else if( rc!=SQLITE_INTERRUPT && (rc&0xFF)!=SQLITE_LOCKED ){
        }else if( rc!=SQLITE_INTERRUPT 
               && (rc&0xFF)!=SQLITE_LOCKED 
               && (rc&0xFF)!=SQLITE_IOERR
        ){
          corruptSchema(pData, argv[0], sqlite3_errmsg(db));
        }
      }
    }
    sqlite3_finalize(pStmt);
  }else if( argv[0]==0 || (argv[2]!=0 && argv[2][0]!=0) ){
    corruptSchema(pData, argv[0], 0);

    }
  }
  assert( pOp->p5==0 || pOp->p4type==P4_INT32 );
  if( pOp->p5
   && (iMeta!=pOp->p3
      || db->aDb[pOp->p1].pSchema->iGeneration!=pOp->p4.i)
  ){
    /*
    ** IMPLEMENTATION-OF: R-03189-51135 As each SQL statement runs, the schema
    ** version is checked to ensure that the schema has not changed since the
    ** SQL statement was prepared.
    */
    sqlite3DbFree(db, p->zErrMsg);
    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    /* If the schema-cookie from the database file matches the cookie 
    ** stored with the in-memory representation of the schema, do
    ** not reload the schema from the database file.
    **
    ** If virtual-tables are in use, this is not just an optimization.
    ** Often, v-tables store their data in other SQLite tables, which
    ** are queried from within xNext() and other v-table methods using
    ** prepared queries. If such a query is out-of-date, we do not want to
    ** discard the database schema, as the user code implementing the
    ** v-table would have to be ready for the sqlite3_vtab structure itself
    ** to be invalidated whenever sqlite3_step() is called from within 
    ** a v-table method.
    */
    if( db->aDb[pOp->p1].pSchema->schema_cookie!=iMeta ){
      sqlite3ResetOneSchema(db, pOp->p1);
    }
    /*
    ** IMPLEMENTATION-OF: R-03189-51135 As each SQL statement runs, the schema
    ** version is checked to ensure that the schema has not changed since the
    ** SQL statement was prepared.
    */
    sqlite3DbFree(db, p->zErrMsg);
    p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
    p->expired = 1;
    rc = SQLITE_SCHEMA;
  }
  if( rc ) goto abort_due_to_error;
  break;
}

  UPDATE sqlite_master SET sql='CREATE TABLE t3(a,b)' WHERE name = 't3';
}

do_test 5.5 { 
  catchsql { SELECT nref,nschema FROM schemapool } db2
} {0 {1 1}}

db2 close
db close
do_test 5.6.1 {
  forcedelete test.db2 test.db2-wal test.db2-journal
  forcecopy test.db test.db2
  sqlite3 db test.db
  sqlite3 db2 test.db  -shared-schema 1
  sqlite3 db3 test.db2 -shared-schema 1
  register_schemapool_module db
} {}

do_execsql_test -db db2 5.6.2 { SELECT * FROM t1 }
do_execsql_test -db db3 5.6.3 { SELECT * FROM t1 }
do_execsql_test 5.6.4 {
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
  CREATE TABLE t4(x);
  DROP TABLE t4;
} {nref=2 nschema=1}
do_execsql_test -db db2 5.6.5 { SELECT * FROM t1 }
do_execsql_test -db db3 5.6.6 { SELECT * FROM t1 }
do_execsql_test 5.6.7 {
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
  ATTACH 'test.db2' AS db2;
  CREATE TABLE db2.t4(x);
  DROP TABLE db2.t4;
} {nref=1 nschema=1 nref=1 nschema=1}
do_execsql_test -db db2 5.6.8 { SELECT * FROM t1 }
do_execsql_test -db db3 5.6.9 { SELECT * FROM t1 }
do_execsql_test 5.6.10 {
  SELECT 'nref=' || nRef, 'nschema=' || nSchema FROM schemapool; 
} {nref=2 nschema=1}

finish_test

# 2019 February 12
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix reusefault

do_execsql_test 1.0 {
  PRAGMA cache_size = 10;
  CREATE TABLE t1(a UNIQUE, b UNIQUE);
  INSERT INTO t1 VALUES(1, 2), (3, 4);
}
faultsim_save_and_close

do_faultsim_test 1.1 -prep {
  faultsim_restore
  sqlite3 db test.db -shared-schema 1
} -body {
  execsql { SELECT * FROM t1 }
} -test {
  faultsim_test_result {0 {1 2 3 4}}
}

do_faultsim_test 1.2 -prep {
  faultsim_restore
  sqlite3 db test.db -shared-schema 1
  execsql { SELECT * FROM t1 }
  sqlite3 db2 test.db
  db2 eval {CREATE TABLE a(a)}
  db2 close
} -body {
  execsql { SELECT  * FROM t1 }
} -test {
  faultsim_test_result {0 {1 2 3 4}}
}


finish_test