/*

 ** 2003 April 6

 **

 ** 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.

 **

 *************************************************************************

 ** This file contains code used to implement the VACUUM command.

 **

 ** Most of the code in this file may be omitted by defining the

 ** SQLITE_OMIT_VACUUM macro.

 **

 ** $Id: vacuum.c,v 1.81 2008/07/08 19:34:07 drh Exp $

 */

 #include "sqliteInt.h"

 #include "vdbeInt.h"

 #if !defined(SQLITE_OMIT_VACUUM) && !defined(SQLITE_OMIT_ATTACH)

 /*

 ** Execute zSql on database db. Return an error code.

 */

 static int execSql(sqlite3 *db, const char *zSql){

   sqlite3_stmt *pStmt;

   if( !zSql ){

     return SQLITE_NOMEM;

   }

   if( SQLITE_OK!=sqlite3_prepare(db, zSql, -1, &pStmt, 0) ){

     return sqlite3_errcode(db);

   }

   while( SQLITE_ROW==sqlite3_step(pStmt) ){}

   return sqlite3_finalize(pStmt);

 }

 /*

 ** Execute zSql on database db. The statement returns exactly

 ** one column. Execute this as SQL on the same database.

 */

 static int execExecSql(sqlite3 *db, const char *zSql){

   sqlite3_stmt *pStmt;

   int rc;

   rc = sqlite3_prepare(db, zSql, -1, &pStmt, 0);

   if( rc!=SQLITE_OK ) return rc;

   while( SQLITE_ROW==sqlite3_step(pStmt) ){

     rc = execSql(db, (char*)sqlite3_column_text(pStmt, 0));

     if( rc!=SQLITE_OK ){

       sqlite3_finalize(pStmt);

       return rc;

     }

   }

   return sqlite3_finalize(pStmt);

 }

 /*

 ** The non-standard VACUUM command is used to clean up the database,

 ** collapse free space, etc.  It is modelled after the VACUUM command

 ** in PostgreSQL.

 **

 ** In version 1.0.x of SQLite, the VACUUM command would call

 ** gdbm_reorganize() on all the database tables.  But beginning

 ** with 2.0.0, SQLite no longer uses GDBM so this command has

 ** become a no-op.

 */

 void sqlite3Vacuum(Parse *pParse){

   Vdbe *v = sqlite3GetVdbe(pParse);

   if( v ){

     sqlite3VdbeAddOp2(v, OP_Vacuum, 0, 0);

   }

   return;

 }

 /*

 ** This routine implements the OP_Vacuum opcode of the VDBE.

 */

 int sqlite3RunVacuum(char **pzErrMsg, sqlite3 *db){

   int rc = SQLITE_OK;     /* Return code from service routines */

   Btree *pMain;           /* The database being vacuumed */

   Btree *pTemp;           /* The temporary database we vacuum into */

   char *zSql = 0;         /* SQL statements */

   int saved_flags;        /* Saved value of the db->flags */

   int saved_nChange;      /* Saved value of db->nChange */

   int saved_nTotalChange; /* Saved value of db->nTotalChange */

   Db *pDb = 0;            /* Database to detach at end of vacuum */

   int nRes;

   /* Save the current value of the write-schema flag before setting it. */

   saved_flags = db->flags;

   saved_nChange = db->nChange;

   saved_nTotalChange = db->nTotalChange;

   db->flags |= SQLITE_WriteSchema | SQLITE_IgnoreChecks;

   if( !db->autoCommit ){

     sqlite3SetString(pzErrMsg, db, "cannot VACUUM from within a transaction");

     rc = SQLITE_ERROR;

     goto end_of_vacuum;

   }

   pMain = db->aDb[0].pBt;

   /* Attach the temporary database as 'vacuum_db'. The synchronous pragma

   ** can be set to 'off' for this file, as it is not recovered if a crash

   ** occurs anyway. The integrity of the database is maintained by a

   ** (possibly synchronous) transaction opened on the main database before

   ** sqlite3BtreeCopyFile() is called.

   **

   ** An optimisation would be to use a non-journaled pager.

   ** (Later:) I tried setting "PRAGMA vacuum_db.journal_mode=OFF" but

   ** that actually made the VACUUM run slower.  Very little journalling

   ** actually occurs when doing a vacuum since the vacuum_db is initially

   ** empty.  Only the journal header is written.  Apparently it takes more

   ** time to parse and run the PRAGMA to turn journalling off than it does

   ** to write the journal header file.

   */

   zSql = "ATTACH '' AS vacuum_db;";

   rc = execSql(db, zSql);

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   pDb = &db->aDb[db->nDb-1];

   assert( strcmp(db->aDb[db->nDb-1].zName,"vacuum_db")==0 );

   pTemp = db->aDb[db->nDb-1].pBt;

   nRes = sqlite3BtreeGetReserve(pMain);

   /* A VACUUM cannot change the pagesize of an encrypted database. */

 #ifdef SQLITE_HAS_CODEC

   if( db->nextPagesize ){

     extern void sqlite3CodecGetKey(sqlite3*, int, void**, int*);

     int nKey;

     char *zKey;

     sqlite3CodecGetKey(db, 0, (void**)&zKey, &nKey);

     if( nKey ) db->nextPagesize = 0;

   }

 #endif

   if( sqlite3BtreeSetPageSize(pTemp, sqlite3BtreeGetPageSize(pMain), nRes)

    || sqlite3BtreeSetPageSize(pTemp, db->nextPagesize, nRes)

    || db->mallocFailed 

   ){

     rc = SQLITE_NOMEM;

     goto end_of_vacuum;

   }

   rc = execSql(db, "PRAGMA vacuum_db.synchronous=OFF");

   if( rc!=SQLITE_OK ){

     goto end_of_vacuum;

   }

 #ifndef SQLITE_OMIT_AUTOVACUUM

   sqlite3BtreeSetAutoVacuum(pTemp, db->nextAutovac>=0 ? db->nextAutovac :

                                            sqlite3BtreeGetAutoVacuum(pMain));

 #endif

   /* Begin a transaction */

   rc = execSql(db, "BEGIN EXCLUSIVE;");

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   /* Query the schema of the main database. Create a mirror schema

   ** in the temporary database.

   */

   rc = execExecSql(db, 

       "SELECT 'CREATE TABLE vacuum_db.' || substr(sql,14) "

       "  FROM sqlite_master WHERE type='table' AND name!='sqlite_sequence'"

       "   AND rootpage>0"

   );

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   rc = execExecSql(db, 

       "SELECT 'CREATE INDEX vacuum_db.' || substr(sql,14)"

       "  FROM sqlite_master WHERE sql LIKE 'CREATE INDEX %' ");

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   rc = execExecSql(db, 

       "SELECT 'CREATE UNIQUE INDEX vacuum_db.' || substr(sql,21) "

       "  FROM sqlite_master WHERE sql LIKE 'CREATE UNIQUE INDEX %'");

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   /* Loop through the tables in the main database. For each, do

   ** an "INSERT INTO vacuum_db.xxx SELECT * FROM xxx;" to copy

   ** the contents to the temporary database.

   */

   rc = execExecSql(db, 

       "SELECT 'INSERT INTO vacuum_db.' || quote(name) "

       "|| ' SELECT * FROM ' || quote(name) || ';'"

       "FROM sqlite_master "

       "WHERE type = 'table' AND name!='sqlite_sequence' "

       "  AND rootpage>0"

   );

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   /* Copy over the sequence table

   */

   rc = execExecSql(db, 

       "SELECT 'DELETE FROM vacuum_db.' || quote(name) || ';' "

       "FROM vacuum_db.sqlite_master WHERE name='sqlite_sequence' "

   );

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   rc = execExecSql(db, 

       "SELECT 'INSERT INTO vacuum_db.' || quote(name) "

       "|| ' SELECT * FROM ' || quote(name) || ';' "

       "FROM vacuum_db.sqlite_master WHERE name=='sqlite_sequence';"

   );

   if( rc!=SQLITE_OK ) goto end_of_vacuum;

   /* Copy the triggers, views, and virtual tables from the main database

   ** over to the temporary database.  None of these objects has any

   ** associated storage, so all we have to do is copy their entries

   ** from the SQLITE_MASTER table.

   */

   rc = execSql(db,

       "INSERT INTO vacuum_db.sqlite_master "

       "  SELECT type, name, tbl_name, rootpage, sql"

       "    FROM sqlite_master"

       "   WHERE type='view' OR type='trigger'"

       "      OR (type='table' AND rootpage=0)"

   );

   if( rc ) goto end_of_vacuum;

   /* At this point, unless the main db was completely empty, there is now a

   ** transaction open on the vacuum database, but not on the main database.

   ** Open a btree level transaction on the main database. This allows a

   ** call to sqlite3BtreeCopyFile(). The main database btree level

   ** transaction is then committed, so the SQL level never knows it was

   ** opened for writing. This way, the SQL transaction used to create the

   ** temporary database never needs to be committed.

   */

   if( rc==SQLITE_OK ){

     u32 meta;

     int i;

     /* This array determines which meta meta values are preserved in the

     ** vacuum.  Even entries are the meta value number and odd entries

     ** are an increment to apply to the meta value after the vacuum.

     ** The increment is used to increase the schema cookie so that other

     ** connections to the same database will know to reread the schema.

     */

     static const unsigned char aCopy[] = {

        1, 1,    /* Add one to the old schema cookie */

        3, 0,    /* Preserve the default page cache size */

        5, 0,    /* Preserve the default text encoding */

        6, 0,    /* Preserve the user version */

     };

     assert( 1==sqlite3BtreeIsInTrans(pTemp) );

     assert( 1==sqlite3BtreeIsInTrans(pMain) );

     /* Copy Btree meta values */

     for(i=0; i<sizeof(aCopy)/sizeof(aCopy[0]); i+=2){

       rc = sqlite3BtreeGetMeta(pMain, aCopy[i], &meta);

       if( rc!=SQLITE_OK ) goto end_of_vacuum;

       rc = sqlite3BtreeUpdateMeta(pTemp, aCopy[i], meta+aCopy[i+1]);

       if( rc!=SQLITE_OK ) goto end_of_vacuum;

     }

     rc = sqlite3BtreeCopyFile(pMain, pTemp);

     if( rc!=SQLITE_OK ) goto end_of_vacuum;

     rc = sqlite3BtreeCommit(pTemp);

     if( rc!=SQLITE_OK ) goto end_of_vacuum;

     rc = sqlite3BtreeCommit(pMain);

   }

   if( rc==SQLITE_OK ){

     rc = sqlite3BtreeSetPageSize(pMain, sqlite3BtreeGetPageSize(pTemp), nRes);

   }

 end_of_vacuum:

   /* Restore the original value of db->flags */

   db->flags = saved_flags;

   db->nChange = saved_nChange;

   db->nTotalChange = saved_nTotalChange;

   /* Currently there is an SQL level transaction open on the vacuum

   ** database. No locks are held on any other files (since the main file

   ** was committed at the btree level). So it safe to end the transaction

   ** by manually setting the autoCommit flag to true and detaching the

   ** vacuum database. The vacuum_db journal file is deleted when the pager

   ** is closed by the DETACH.

   */

   db->autoCommit = 1;

   if( pDb ){

     sqlite3BtreeClose(pDb->pBt);

     pDb->pBt = 0;

     pDb->pSchema = 0;

   }

   sqlite3ResetInternalSchema(db, 0);

   return rc;

 }

 #endif  /* SQLITE_OMIT_VACUUM && SQLITE_OMIT_ATTACH */