/*

** 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 1.83 2008/08/26 21:07:27 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 */

  Pager *pMainPager;      /* Pager for 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 isMemDb;            /* True is vacuuming a :memory: database */

  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;

  pMainPager = sqlite3BtreePager(pMain);

  isMemDb = sqlite3PagerFile(pMainPager)->pMethods==0;

  /* 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)

   || (!isMemDb && 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;

#ifndef SQLITE_OMIT_AUTOVACUUM

    sqlite3BtreeSetAutoVacuum(pMain, sqlite3BtreeGetAutoVacuum(pTemp));

#endif

    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 */