/*
** 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.
*/
#include "sqliteInt.h"
#include "vdbeInt.h"
#if !defined(SQLITE_OMIT_VACUUM) && !defined(SQLITE_OMIT_ATTACH)
/*
** Execute zSql on database db.
**
** If zSql returns rows, then each row will have exactly one
** column. (This will only happen if zSql begins with "SELECT".)
** Take each row of result and call execSql() again recursively.
**
** The execSqlF() routine does the same thing, except it accepts
** a format string as its third argument
*/
static int execSql(sqlite3 *db, char **pzErrMsg, const char *zSql){
sqlite3_stmt *pStmt;
int rc;
/* printf("SQL: [%s]\n", zSql); fflush(stdout); */
rc = sqlite3_prepare_v2(db, zSql, -1, &pStmt, 0);
if( rc!=SQLITE_OK ) return rc;
while( SQLITE_ROW==(rc = sqlite3_step(pStmt)) ){
const char *zSubSql = (const char*)sqlite3_column_text(pStmt,0);
assert( sqlite3_strnicmp(zSql,"SELECT",6)==0 );
/* The secondary SQL must be one of CREATE TABLE, CREATE INDEX,
** or INSERT. Historically there have been attacks that first
** corrupt the sqlite_master.sql field with other kinds of statements
** then run VACUUM to get those statements to execute at inappropriate
** times. */
if( zSubSql
&& (strncmp(zSubSql,"CRE",3)==0 || strncmp(zSubSql,"INS",3)==0)
){
rc = execSql(db, pzErrMsg, zSubSql);
if( rc!=SQLITE_OK ) break;
}
}
assert( rc!=SQLITE_ROW );
if( rc==SQLITE_DONE ) rc = SQLITE_OK;
if( rc ){
sqlite3SetString(pzErrMsg, db, sqlite3_errmsg(db));
}
(void)sqlite3_finalize(pStmt);
return rc;
}
static int execSqlF(sqlite3 *db, char **pzErrMsg, const char *zSql, ...){
char *z;
va_list ap;
int rc;
va_start(ap, zSql);
z = sqlite3VMPrintf(db, zSql, ap);
va_end(ap);
if( z==0 ) return SQLITE_NOMEM;
rc = execSql(db, pzErrMsg, z);
sqlite3DbFree(db, z);
return rc;
}
/*
** The VACUUM command is used to clean up the database,
** collapse free space, etc. It is modelled after the VACUUM command
** in PostgreSQL. The VACUUM command works as follows:
**
** (1) Create a new transient database file
** (2) Copy all content from the database being vacuumed into
** the new transient database file
** (3) Copy content from the transient database back into the
** original database.
**
** The transient database requires temporary disk space approximately
** equal to the size of the original database. The copy operation of
** step (3) requires additional temporary disk space approximately equal
** to the size of the original database for the rollback journal.
** Hence, temporary disk space that is approximately 2x the size of the
** original database is required. Every page of the database is written
** approximately 3 times: Once for step (2) and twice for step (3).
** Two writes per page are required in step (3) because the original
** database content must be written into the rollback journal prior to
** overwriting the database with the vacuumed content.
**
** Only 1x temporary space and only 1x writes would be required if
** the copy of step (3) were replaced by deleting the original database
** and renaming the transient database as the original. But that will
** not work if other processes are attached to the original database.
** And a power loss in between deleting the original and renaming the
** transient would cause the database file to appear to be deleted
** following reboot.
*/
void sqlite3Vacuum(Parse *pParse, Token *pNm){
Vdbe *v = sqlite3GetVdbe(pParse);
int iDb = 0;
if( v==0 ) return;
if( pNm ){
#ifndef SQLITE_BUG_COMPATIBLE_20160819
/* Default behavior: Report an error if the argument to VACUUM is
** not recognized */
iDb = sqlite3TwoPartName(pParse, pNm, pNm, &pNm);
if( iDb<0 ) return;
#else
/* When SQLITE_BUG_COMPATIBLE_20160819 is defined, unrecognized arguments
** to VACUUM are silently ignored. This is a back-out of a bug fix that
** occurred on 2016-08-19 (https://www.sqlite.org/src/info/083f9e6270).
** The buggy behavior is required for binary compatibility with some
** legacy applications. */
iDb = sqlite3FindDb(pParse->db, pNm);
if( iDb<0 ) iDb = 0;
#endif
}
if( iDb!=1 ){
sqlite3VdbeAddOp1(v, OP_Vacuum, iDb);
sqlite3VdbeUsesBtree(v, iDb);
}
return;
}
/*
** This routine implements the OP_Vacuum opcode of the VDBE.
*/
int sqlite3RunVacuum(char **pzErrMsg, sqlite3 *db, int iDb){
int rc = SQLITE_OK; /* Return code from service routines */
Btree *pMain; /* The database being vacuumed */
Btree *pTemp; /* The temporary database we vacuum into */
u16 saved_mDbFlags; /* Saved value of db->mDbFlags */
u32 saved_flags; /* Saved value of db->flags */
int saved_nChange; /* Saved value of db->nChange */
int saved_nTotalChange; /* Saved value of db->nTotalChange */
u8 saved_mTrace; /* Saved trace settings */
Db *pDb = 0; /* Database to detach at end of vacuum */
int isMemDb; /* True if vacuuming a :memory: database */
int nRes; /* Bytes of reserved space at the end of each page */
int nDb; /* Number of attached databases */
const char *zDbMain; /* Schema name of database to vacuum */
if( !db->autoCommit ){
sqlite3SetString(pzErrMsg, db, "cannot VACUUM from within a transaction");
return SQLITE_ERROR;
}
if( db->nVdbeActive>1 ){
sqlite3SetString(pzErrMsg, db,"cannot VACUUM - SQL statements in progress");
return SQLITE_ERROR;
}
/* Save the current value of the database flags so that it can be
** restored before returning. Then set the writable-schema flag, and
** disable CHECK and foreign key constraints. */
saved_flags = db->flags;
saved_mDbFlags = db->mDbFlags;
saved_nChange = db->nChange;
saved_nTotalChange = db->nTotalChange;
saved_mTrace = db->mTrace;
db->flags |= SQLITE_WriteSchema | SQLITE_IgnoreChecks;
db->mDbFlags |= DBFLAG_PreferBuiltin | DBFLAG_Vacuum;
db->flags &= ~(SQLITE_ForeignKeys | SQLITE_ReverseOrder | SQLITE_CountRows);
db->mTrace = 0;
zDbMain = db->aDb[iDb].zDbSName;
pMain = db->aDb[iDb].pBt;
isMemDb = sqlite3PagerIsMemdb(sqlite3BtreePager(pMain));
/* 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.
*/
nDb = db->nDb;
rc = execSql(db, pzErrMsg, "ATTACH''AS vacuum_db");
if( rc!=SQLITE_OK ) goto end_of_vacuum;
assert( (db->nDb-1)==nDb );
pDb = &db->aDb[nDb];
assert( strcmp(pDb->zDbSName,"vacuum_db")==0 );
pTemp = pDb->pBt;
/* The call to execSql() to attach the temp database has left the file
** locked (as there was more than one active statement when the transaction
** to read the schema was concluded. Unlock it here so that this doesn't
** cause problems for the call to BtreeSetPageSize() below. */
sqlite3BtreeCommit(pTemp);
nRes = sqlite3BtreeGetOptimalReserve(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, iDb, (void**)&zKey, &nKey);
if( nKey ) db->nextPagesize = 0;
}
#endif
sqlite3BtreeSetCacheSize(pTemp, db->aDb[iDb].pSchema->cache_size);
sqlite3BtreeSetSpillSize(pTemp, sqlite3BtreeSetSpillSize(pMain,0));
sqlite3BtreeSetPagerFlags(pTemp, PAGER_SYNCHRONOUS_OFF|PAGER_CACHESPILL);
/* Begin a transaction and take an exclusive lock on the main database
** file. This is done before the sqlite3BtreeGetPageSize(pMain) call below,
** to ensure that we do not try to change the page-size on a WAL database.
*/
rc = execSql(db, pzErrMsg, "BEGIN");
if( rc!=SQLITE_OK ) goto end_of_vacuum;
rc = sqlite3BtreeBeginTrans(pMain, 2);
if( rc!=SQLITE_OK ) goto end_of_vacuum;
/* Do not attempt to change the page size for a WAL database */
if( sqlite3PagerGetJournalMode(sqlite3BtreePager(pMain))
==PAGER_JOURNALMODE_WAL ){
db->nextPagesize = 0;
}
if( sqlite3BtreeSetPageSize(pTemp, sqlite3BtreeGetPageSize(pMain), nRes, 0)
|| (!isMemDb && sqlite3BtreeSetPageSize(pTemp, db->nextPagesize, nRes, 0))
|| NEVER(db->mallocFailed)
){
rc = SQLITE_NOMEM_BKPT;
goto end_of_vacuum;
}
#ifndef SQLITE_OMIT_AUTOVACUUM
sqlite3BtreeSetAutoVacuum(pTemp, db->nextAutovac>=0 ? db->nextAutovac :
sqlite3BtreeGetAutoVacuum(pMain));
#endif
/* Query the schema of the main database. Create a mirror schema
** in the temporary database.
*/
db->init.iDb = nDb; /* force new CREATE statements into vacuum_db */
rc = execSqlF(db, pzErrMsg,
"SELECT sql FROM \"%w\".sqlite_master"
" WHERE type='table'AND name<>'sqlite_sequence'"
" AND coalesce(rootpage,1)>0",
zDbMain
);
if( rc!=SQLITE_OK ) goto end_of_vacuum;
rc = execSqlF(db, pzErrMsg,
"SELECT sql FROM \"%w\".sqlite_master"
" WHERE type='index'",
zDbMain
);
if( rc!=SQLITE_OK ) goto end_of_vacuum;
db->init.iDb = 0;
/* Loop through the tables in the main database. For each, do
** an "INSERT INTO vacuum_db.xxx SELECT * FROM main.xxx;" to copy
** the contents to the temporary database.
*/
rc = execSqlF(db, pzErrMsg,
"SELECT'INSERT INTO vacuum_db.'||quote(name)"
"||' SELECT*FROM\"%w\".'||quote(name)"
"FROM vacuum_db.sqlite_master "
"WHERE type='table'AND coalesce(rootpage,1)>0",
zDbMain
);
assert( (db->mDbFlags & DBFLAG_Vacuum)!=0 );
db->mDbFlags &= ~DBFLAG_Vacuum;
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 = execSqlF(db, pzErrMsg,
"INSERT INTO vacuum_db.sqlite_master"
" SELECT*FROM \"%w\".sqlite_master"
" WHERE type IN('view','trigger')"
" OR(type='table'AND rootpage=0)",
zDbMain
);
if( rc ) goto end_of_vacuum;
/* At this point, there is a write transaction open on both the
** vacuum database and the main database. Assuming no error occurs,
** both transactions are closed by this block - the main database
** transaction by sqlite3BtreeCopyFile() and the other by an explicit
** call to sqlite3BtreeCommit().
*/
{
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[] = {
BTREE_SCHEMA_VERSION, 1, /* Add one to the old schema cookie */
BTREE_DEFAULT_CACHE_SIZE, 0, /* Preserve the default page cache size */
BTREE_TEXT_ENCODING, 0, /* Preserve the text encoding */
BTREE_USER_VERSION, 0, /* Preserve the user version */
BTREE_APPLICATION_ID, 0, /* Preserve the application id */
};
assert( 1==sqlite3BtreeIsInTrans(pTemp) );
assert( 1==sqlite3BtreeIsInTrans(pMain) );
/* Copy Btree meta values */
for(i=0; i<ArraySize(aCopy); i+=2){
/* GetMeta() and UpdateMeta() cannot fail in this context because
** we already have page 1 loaded into cache and marked dirty. */
sqlite3BtreeGetMeta(pMain, aCopy[i], &meta);
rc = sqlite3BtreeUpdateMeta(pTemp, aCopy[i], meta+aCopy[i+1]);
if( NEVER(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
}
assert( rc==SQLITE_OK );
rc = sqlite3BtreeSetPageSize(pMain, sqlite3BtreeGetPageSize(pTemp), nRes,1);
end_of_vacuum:
/* Restore the original value of db->flags */
db->init.iDb = 0;
db->mDbFlags = saved_mDbFlags;
db->flags = saved_flags;
db->nChange = saved_nChange;
db->nTotalChange = saved_nTotalChange;
db->mTrace = saved_mTrace;
sqlite3BtreeSetPageSize(pMain, -1, -1, 1);
/* 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;
}
/* This both clears the schemas and reduces the size of the db->aDb[]
** array. */
sqlite3ResetAllSchemasOfConnection(db);
return rc;
}
#endif /* SQLITE_OMIT_VACUUM && SQLITE_OMIT_ATTACH */