public static RC RunVacuum(ref string errMsg, Context ctx)
{
if (ctx.AutoCommit == 0)
{
C._setstring(ref errMsg, ctx, "cannot VACUUM from within a transaction");
return(RC.ERROR);
}
if (ctx.ActiveVdbeCnt > 1)
{
C._setstring(ref errMsg, ctx, "cannot VACUUM - SQL statements in progress");
return(RC.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.
int saved_Flags = ctx.Flags; // Saved value of the db.flags
int saved_Changes = ctx.Changes; // Saved value of db.nChange
int saved_TotalChanges = ctx.TotalChanges; // Saved value of db.nTotalChange
Action <object, string> saved_Trace = ctx.Trace; // Saved db->xTrace
ctx.Flags |= Context.FLAG.WriteSchema | Context.FLAG.IgnoreChecks | Context.FLAG.PreferBuiltin;
ctx.Flags &= ~(Context.FLAG.ForeignKeys | Context.FLAG.ReverseOrder);
ctx.Trace = null;
Btree main = ctx.DBs[0].Bt; // The database being vacuumed
bool isMemDb = sqlite3PagerIsMemdb(main.get_Pager()); // True if vacuuming a :memory: database
// 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.
int db = ctx.DBs.length; // Number of attached databases
string sql = (sqlite3TempInMemory(ctx) ? "ATTACH ':memory:' AS vacuum_db;" : "ATTACH '' AS vacuum_db;"); // SQL statements
RC rc = ExecSql(ctx, errMsg, sql); // Return code from service routines
Context.DB dbObj = null; // Database to detach at end of vacuum
if (ctx.DBs.length > db)
{
dbObj = ctx.DBs[ctx.DBs.length - 1];
Debug.Assert(dbObj.Name == "vacuum_db");
}
if (rc != RC.OK)
{
goto end_of_vacuum;
}
Btree temp = ctx.DBs[ctx.DBs.length - 1].Bt; // The temporary database we vacuum into
// 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.
temp.Commit();
int res = main.GetReserve(); // Bytes of reserved space at the end of each page
// A VACUUM cannot change the pagesize of an encrypted database.
#if HAS_CODEC
if (ctx.NextPagesize != 0)
{
int nKey;
string zKey;
sqlite3CodecGetKey(ctx, 0, out zKey, out nKey);
if (nKey != 0)
{
ctx.NextPagesize = 0;
}
}
#endif
rc = ExecSql(ctx, errMsg, "PRAGMA vacuum_db.synchronous=OFF");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
// Begin a transaction and take an exclusive lock on the main database file. This is done before the sqlite3BtreeGetPageSize(main) call below,
// to ensure that we do not try to change the page-size on a WAL database.
rc = ExecSql(ctx, errMsg, "BEGIN;");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
rc = main.BeginTrans(2);
if (rc != RC.OK)
{
goto end_of_vacuum;
}
// Do not attempt to change the page size for a WAL database
if (main.get_Pager().GetJournalMode() == IPager.JOURNALMODE.WAL)
{
ctx.NextPagesize = 0;
}
if (temp.SetPageSize(main.GetPageSize(), res, 0) != 0 || (!isMemDb && temp.SetPageSize(ctx->NextPagesize, res, false) != 0) || C._NEVER(ctx.MallocFailed))
{
rc = RC.NOMEM;
goto end_of_vacuum;
}
#if !OMIT_AUTOVACUUM
temp.SetAutoVacuum(ctx.NextAutovac >= 0 ? ctx.NextAutovac : main.GetAutoVacuum());
#endif
// Query the schema of the main database. Create a mirror schema in the temporary database.
rc = ExecExecSql(ctx, errMsg,
"SELECT 'CREATE TABLE vacuum_db.' || substr(sql,14) " +
" FROM sqlite_master WHERE type='table' AND name!='sqlite_sequence'" +
" AND rootpage>0"
);
if (rc != RC.OK)
{
goto end_of_vacuum;
}
rc = ExecExecSql(ctx, errMsg,
"SELECT 'CREATE INDEX vacuum_db.' || substr(sql,14)" +
" FROM sqlite_master WHERE sql LIKE 'CREATE INDEX %' ");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
rc = ExecExecSql(ctx, errMsg,
"SELECT 'CREATE UNIQUE INDEX vacuum_db.' || substr(sql,21) " +
" FROM sqlite_master WHERE sql LIKE 'CREATE UNIQUE INDEX %'");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
// 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 = ExecExecSql(ctx, errMsg,
"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");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
// Copy over the sequence table
rc = ExecExecSql(ctx, errMsg,
"SELECT 'DELETE FROM vacuum_db.' || quote(name) || ';' " +
"FROM vacuum_db.sqlite_master WHERE name='sqlite_sequence' ");
if (rc != RC.OK)
{
goto end_of_vacuum;
}
rc = ExecExecSql(ctx, errMsg,
"SELECT 'INSERT INTO vacuum_db.' || quote(name) " +
"|| ' SELECT * FROM main.' || quote(name) || ';' " +
"FROM vacuum_db.sqlite_master WHERE name=='sqlite_sequence';");
if (rc != RC.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(ctx, errMsg,
"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)");
if (rc != 0)
{
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().
{
// 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.
Debug.Assert(Btree.IsInTrans(temp));
Debug.Assert(Btree.IsInTrans(main));
// Copy Btree meta values
for (int i = 0; i < _runVacuum_copy.Length; i += 2)
{
// GetMeta() and UpdateMeta() cannot fail in this context because we already have page 1 loaded into cache and marked dirty.
uint meta = 0;
main.GetMeta(_runVacuum_copy[i], ref meta);
rc = temp.UpdateMeta(temp, _runVacuum_copy[i], (uint)(meta + _runVacuum_copy[i + 1]));
if (C._NEVER(rc != RC.OK))
{
goto end_of_vacuum;
}
}
rc = sqlite3BtreeCopyFile(main, temp);
if (rc != RC.OK)
{
goto end_of_vacuum;
}
rc = temp.Commit();
if (rc != RC.OK)
{
goto end_of_vacuum;
}
#if !SQLITE_OMIT_AUTOVACUUM
main.SetAutoVacuum(temp.GetAutoVacuum());
#endif
}
Debug.Assert(rc == RC.OK);
rc = main.SetPageSize(temp.GetPageSize(temp), res, 1);
end_of_vacuum:
// Restore the original value of ctx->flags
ctx.Flags = saved_Flags;
ctx.Changes = saved_Changes;
ctx.TotalChanges = saved_TotalChanges;
ctx.Trace = saved_Trace;
sqlite3BtreeSetPageSize(main, -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.
ctx.AutoCommit = 1;
if (dbObj != null)
{
dbObj.Bt.Close();
dbObj.Bt = null;
dbObj.Schema = null;
}
// This both clears the schemas and reduces the size of the db->aDb[] array.
sqlite3ResetInternalSchema(ctx, -1);
return(rc);
}
