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+/*
+** 2013-10-01
+**
+** 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 program implements a high-speed version of the VACUUM command.
+** It repacks an SQLite database to remove as much unused space as
+** possible and to relocate content sequentially in the file.
+**
+** This program runs faster and uses less temporary disk space than the
+** built-in VACUUM command. On the other hand, this program has a number
+** of important restrictions relative to the built-in VACUUM command.
+**
+** (1) The caller must ensure that no other processes are accessing the
+** database file while the vacuum is taking place. The usual SQLite
+** file locking is insufficient for this. The caller must use
+** external means to make sure only this one routine is reading and
+** writing the database.
+**
+** (2) Database reconfiguration such as page size or auto_vacuum changes
+** are not supported by this utility.
+**
+** (3) The database file might be renamed if a power loss or crash
+** occurs at just the wrong moment. Recovery must be prepared to
+** to deal with the possibly changed filename.
+**
+** This program is intended as a *Demonstration Only*. The intent of this
+** program is to provide example code that application developers can use
+** when creating similar functionality in their applications.
+**
+** To compile this program:
+**
+** cc fast_vacuum.c sqlite3.c
+**
+** Add whatever linker options are required. (Example: "-ldl -lpthread").
+** Then to run the program:
+**
+** ./a.out file-to-vacuum
+**
+*/
+#include "sqlite3.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+** Finalize a prepared statement. If an error has occurred, print the
+** error message and exit.
+*/
+static void vacuumFinalize(sqlite3_stmt *pStmt){
+ sqlite3 *db = sqlite3_db_handle(pStmt);
+ int rc = sqlite3_finalize(pStmt);
+ if( rc ){
+ fprintf(stderr, "finalize error: %s\n", sqlite3_errmsg(db));
+ exit(1);
+ }
+}
+
+/*
+** Execute zSql on database db. The SQL text is printed to standard
+** output. If an error occurs, print an error message and exit the
+** process.
+*/
+static void execSql(sqlite3 *db, const char *zSql){
+ sqlite3_stmt *pStmt;
+ if( !zSql ){
+ fprintf(stderr, "out of memory!\n");
+ exit(1);
+ }
+ printf("%s;\n", zSql);
+ if( SQLITE_OK!=sqlite3_prepare(db, zSql, -1, &pStmt, 0) ){
+ fprintf(stderr, "Error: %s\n", sqlite3_errmsg(db));
+ exit(1);
+ }
+ sqlite3_step(pStmt);
+ vacuumFinalize(pStmt);
+}
+
+/*
+** Execute zSql on database db. The zSql statement returns exactly
+** one column. Execute this return value as SQL on the same database.
+**
+** The zSql statement is printed on standard output prior to being
+** run. If any errors occur, an error is printed and the process
+** exits.
+*/
+static void execExecSql(sqlite3 *db, const char *zSql){
+ sqlite3_stmt *pStmt;
+ int rc;
+
+ printf("%s;\n", zSql);
+ rc = sqlite3_prepare(db, zSql, -1, &pStmt, 0);
+ if( rc!=SQLITE_OK ){
+ fprintf(stderr, "Error: %s\n", sqlite3_errmsg(db));
+ exit(1);
+ }
+ while( SQLITE_ROW==sqlite3_step(pStmt) ){
+ execSql(db, (char*)sqlite3_column_text(pStmt, 0));
+ }
+ vacuumFinalize(pStmt);
+}
+
+
+int main(int argc, char **argv){
+ sqlite3 *db; /* Connection to the database file */
+ int rc; /* Return code from SQLite interface calls */
+ sqlite3_uint64 r; /* A random number */
+ const char *zDbToVacuum; /* Database to be vacuumed */
+ char *zBackupDb; /* Backup copy of the original database */
+ char *zTempDb; /* Temporary database */
+ char *zSql; /* An SQL statement */
+
+ if( argc!=2 ){
+ fprintf(stderr, "Usage: %s DATABASE\n", argv[0]);
+ return 1;
+ }
+
+ /* Identify the database file to be vacuumed and open it.
+ */
+ zDbToVacuum = argv[1];
+ printf("-- open database file \"%s\"\n", zDbToVacuum);
+ rc = sqlite3_open(zDbToVacuum, &db);
+ if( rc ){
+ fprintf(stderr, "%s: %s\n", zDbToVacuum, sqlite3_errstr(rc));
+ return 1;
+ }
+
+ /* Create names for two other files. zTempDb will be a new database
+ ** into which we construct a vacuumed copy of zDbToVacuum. zBackupDb
+ ** will be a new name for zDbToVacuum after it is vacuumed.
+ */
+ sqlite3_randomness(sizeof(r), &r);
+ zTempDb = sqlite3_mprintf("%s-vacuum-%016llx", zDbToVacuum, r);
+ zBackupDb = sqlite3_mprintf("%s-backup-%016llx", zDbToVacuum, r);
+
+ /* Attach the zTempDb database to the database connection.
+ */
+ zSql = sqlite3_mprintf("ATTACH '%q' AS vacuum_db;", zTempDb);
+ execSql(db, zSql);
+ sqlite3_free(zSql);
+
+ /* TODO:
+ ** Set the page_size and auto_vacuum mode for zTempDb here, if desired.
+ */
+
+ /* The vacuum will occur inside of a transaction. Set writable_schema
+ ** to ON so that we can directly update the sqlite_master table in the
+ ** zTempDb database.
+ */
+ execSql(db, "PRAGMA writable_schema=ON");
+ execSql(db, "BEGIN");
+
+
+ /* Query the schema of the main database. Create a mirror schema
+ ** in the temporary database.
+ */
+ execExecSql(db,
+ "SELECT 'CREATE TABLE vacuum_db.' || substr(sql,14) "
+ " FROM sqlite_master WHERE type='table' AND name!='sqlite_sequence'"
+ " AND rootpage>0"
+ );
+ execExecSql(db,
+ "SELECT 'CREATE INDEX vacuum_db.' || substr(sql,14)"
+ " FROM sqlite_master WHERE sql LIKE 'CREATE INDEX %'"
+ );
+ execExecSql(db,
+ "SELECT 'CREATE UNIQUE INDEX vacuum_db.' || substr(sql,21) "
+ " FROM sqlite_master WHERE sql LIKE 'CREATE UNIQUE INDEX %'"
+ );
+
+ /* 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.
+ */
+ execExecSql(db,
+ "SELECT 'INSERT INTO vacuum_db.' || quote(name) "
+ "|| ' SELECT * FROM main.' || quote(name) "
+ "FROM main.sqlite_master "
+ "WHERE type = 'table' AND name!='sqlite_sequence' "
+ " AND rootpage>0"
+ );
+
+ /* Copy over the sequence table
+ */
+ execExecSql(db,
+ "SELECT 'DELETE FROM vacuum_db.' || quote(name) "
+ "FROM vacuum_db.sqlite_master WHERE name='sqlite_sequence'"
+ );
+ execExecSql(db,
+ "SELECT 'INSERT INTO vacuum_db.' || quote(name) "
+ "|| ' SELECT * FROM main.' || quote(name) "
+ "FROM vacuum_db.sqlite_master WHERE name=='sqlite_sequence'"
+ );
+
+ /* 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.
+ */
+ execSql(db,
+ "INSERT INTO vacuum_db.sqlite_master "
+ " SELECT type, name, tbl_name, rootpage, sql"
+ " FROM main.sqlite_master"
+ " WHERE type='view' OR type='trigger'"
+ " OR (type='table' AND rootpage=0)"
+ );
+
+ /* Commit the transaction and close the database
+ */
+ execSql(db, "COMMIT");
+ printf("-- close database\n");
+ sqlite3_close(db);
+
+
+ /* At this point, zDbToVacuum is unchanged. zTempDb contains a
+ ** vacuumed copy of zDbToVacuum. Rearrange filenames so that
+ ** zTempDb becomes thenew zDbToVacuum.
+ */
+ printf("-- rename \"%s\" to \"%s\"\n", zDbToVacuum, zBackupDb);
+ rename(zDbToVacuum, zBackupDb);
+ printf("-- rename \"%s\" to \"%s\"\n", zTempDb, zDbToVacuum);
+ rename(zTempDb, zDbToVacuum);
+
+ /* Release allocated memory */
+ sqlite3_free(zTempDb);
+ sqlite3_free(zBackupDb);
+ return 0;
+}