SQLite

If the schema of a database attached to an
SQLITE_OPEN_SHARED_SCHEMA database handle is corrupt, or if
corruption is encountered while parsing the database schema, then the
database is treated as empty. This usually means that corruption results in
a "no such table: xxx" error instead of a more specific error message.

For SQLITE_OPEN_SHARED_SCHEMA connections, the
SQLITE_DBSTATUS_SCHEMA_USED sqlite3_db_status() verb
distributes the memory used for a shared schema object evenly between all
database connections that share it.

## Implementation Notes

A single Schema object is never used by more than one database simultaneously,
regardless of whether or not those databases are attached to the same or
different database handles. Instead, a pool of schema objects is maintained 
for each unique sqlite_master-contents/schema-cookie combination

**
** If the database handle was not opened with SQLITE_OPEN_SHARED_SCHEMA, or
** if the schema for database iDb is already loaded, this function is a no-op.
**
** Non-zero is returned if a schema is loaded, or zero if it was already 
** loaded when this function was called..
*/
int sqlite3SchemaLoad(sqlite3 *db, int iDb){
  if( IsReuseSchema(db) 
   && DbHasProperty(db, iDb, DB_SchemaLoaded)==0 
   && (db->init.busy==0 || (iDb!=1 && db->init.iDb==1))
  ){
    char *zDummy = 0;
    struct sqlite3InitInfo sv = db->init;
    memset(&db->init, 0, sizeof(struct sqlite3InitInfo));

#endif
  while(1){
    for(i=OMIT_TEMPDB; i<db->nDb; i++){
      int j = (i<2) ? i^1 : i;   /* Search TEMP before MAIN */
      if( zDatabase==0 || sqlite3StrICmp(zDatabase, db->aDb[j].zDbSName)==0 ){
        int bUnload;
        assert( sqlite3SchemaMutexHeld(db, j, 0) );
        bUnload = sqlite3SchemaLoad(db, j);
        p = sqlite3HashFind(&db->aDb[j].pSchema->tblHash, zName);
        if( p ) return p;
        if( bUnload ){
          sqlite3SchemaRelease(db, j);
        }
      }
    }

    ** can be an eponymous virtual table. */
    if( pParse->disableVtab==0 ){
      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) ){
          return pMod->pEpoTab;
        }
      }
    }
#endif
    if( flags & LOCATE_NOERR ) return 0;

#ifdef SQLITE_TEST
/*
** Return a pointer to the head of the linked list of SchemaPool objects.
** This is used by the virtual table in file test_schemapool.c.
*/
SchemaPool *sqlite3SchemaPoolList(void){ return schemaPoolList; }
#endif

/*
** Database handle db was opened with the SHARED_SCHEMA flag, and database
** iDb is currently connected to a schema-pool. When this function is called,
** (*pnByte) is set to nInit plus the amount of memory used to store a 
** single instance of the Schema objects managed by the schema-pool.
** This function adjusts (*pnByte) sot hat it is set to nInit plus
** (nSchema/nRef) of the amount of memory used by a single Schema object,
** where nSchema is the number of Schema objects allocated by this pool,
** and nRef is the number of connections to the schema-pool.
*/
void sqlite3SchemaAdjustUsed(sqlite3 *db, int iDb, int nInit, int *pnByte){
  SchemaPool *pSPool = db->aDb[iDb].pSPool;
  int nSchema = 0;
  Schema *p;
  sqlite3_mutex_enter( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
  for(p=pSPool->pSchema; p; p=p->pNext){
    nSchema++;
  }
  *pnByte = nInit + ((*pnByte - nInit) * nSchema) / pSPool->nRef;
  sqlite3_mutex_leave( sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER) );
}

/*
** Check that the schema of db iDb is writable (either because it is the 
** temp db schema or because the db handle was opened without
** SQLITE_OPEN_SHARED_SCHEMA). If so, do nothing. Otherwise, leave an 
** error in the Parse object.
*/

void sqlite3RegisterLikeFunctions(sqlite3*, int);
int sqlite3IsLikeFunction(sqlite3*,Expr*,int*,char*);
void sqlite3SchemaClear(void *);
int sqlite3SchemaConnect(sqlite3*, int, u64);
int sqlite3SchemaDisconnect(sqlite3 *, int, int);
void sqlite3SchemaClearOrDisconnect(sqlite3*, int);
Schema *sqlite3SchemaExtract(SchemaPool*);
int sqlite3SchemaLoad(sqlite3*, int);
void sqlite3SchemaReleaseAll(sqlite3*);
void sqlite3SchemaRelease(sqlite3*, int);
void sqlite3SchemaAdjustUsed(sqlite3*, int, int, int*);
void sqlite3SchemaWritable(Parse*, int);
Schema *sqlite3SchemaGet(sqlite3 *, Btree *);
int sqlite3SchemaToIndex(sqlite3 *db, Schema *);
KeyInfo *sqlite3KeyInfoAlloc(sqlite3*,int,int);
void sqlite3KeyInfoUnref(KeyInfo*);
KeyInfo *sqlite3KeyInfoRef(KeyInfo*);
KeyInfo *sqlite3KeyInfoOfIndex(Parse*, Index*);

    ** *pCurrent gets an accurate estimate of the amount of memory used
    ** to store the schema for all databases (main, temp, and any ATTACHed
    ** databases.  *pHighwater is set to zero.
    */
    case SQLITE_DBSTATUS_SCHEMA_USED: {
      int i;                      /* Used to iterate through schemas */
      int nByte = 0;              /* Used to accumulate return value */
      int bReleaseSchema;

      sqlite3BtreeEnterAll(db);
      bReleaseSchema = sqlite3LockReusableSchema(db);
      db->pnBytesFreed = &nByte;
      for(i=0; i<db->nDb; i++){
        int bUnload = 0;
        int nUsed = nByte;
        Schema *pSchema;
        if( db->aDb[i].pSPool ){
          bUnload = sqlite3SchemaLoad(db, i);
        }
        pSchema = db->aDb[i].pSchema;
        if( ALWAYS(pSchema!=0) ){
          HashElem *p;

          nByte += sqlite3GlobalConfig.m.xRoundup(sizeof(HashElem)) * (
              pSchema->tblHash.count 
            + pSchema->trigHash.count
            + pSchema->idxHash.count

          for(p=sqliteHashFirst(&pSchema->trigHash); p; p=sqliteHashNext(p)){
            sqlite3DeleteTrigger(db, (Trigger*)sqliteHashData(p));
          }
          for(p=sqliteHashFirst(&pSchema->tblHash); p; p=sqliteHashNext(p)){
            sqlite3DeleteTable(db, (Table *)sqliteHashData(p));
          }
        }
        if( db->aDb[i].pSPool ){
          if( bUnload ) sqlite3SchemaRelease(db, i);
          sqlite3SchemaAdjustUsed(db, i, nUsed, &nByte);
        }
      }
      sqlite3UnlockReusableSchema(db, bReleaseSchema);
      db->pnBytesFreed = 0;
      sqlite3BtreeLeaveAll(db);

      *pHighwater = 0;
      *pCurrent = nByte;
      break;
    }

do_catchsql_test 2.1 {
  SELECT * FROM x1;
} {1 {no such table: x1}}

do_catchsql_test 2.2 {
  SELECT * FROM x1;
} {1 {no such table: x1}}

#-------------------------------------------------------------------------
reset_db
do_execsql_test 3.0 {
  CREATE TABLE x1(a, b, c);
  CREATE INDEX i1 ON x1(a, b, c);
  CREATE TRIGGER tr1 AFTER INSERT ON x1 BEGIN
    SELECT 1, 2, 3, 4, 5;
  END;
  INSERT INTO x1 VALUES(1, 2, 3);
}
sqlite3 db1 test.db -shared-schema 1

do_test 3.1 {
  execsql { SELECT * FROM x1 } db1
  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
  breakpoint
  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

finish_test

catch {sqlite3}

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

# Check the error messages generated by tclsqlite
#
set r "sqlite_orig HANDLE ?FILENAME? ?-vfs VFSNAME? ?-readonly BOOLEAN? ?-create BOOLEAN? ?-nomutex BOOLEAN? ?-fullmutex BOOLEAN? ?-uri BOOLEAN? ?-shared-schema BOOLEAN?"
if {[sqlite3 -has-codec]} {
  append r " ?-key CODECKEY?"
}
do_test tcl-1.1 {
  set v [catch {sqlite3 -bogus} msg]
  regsub {really_sqlite3} $msg {sqlite3} msg
  lappend v $msg