3. How VACUUM works The VACUUM command works by copying the contents of the database into a short-lived database file and then overwriting the initial with the contents of the momentary file. When overwriting the original, a rollback journal or write-ahead log WAL file is used simply as it would be for any other database deal.
The VACUUM INTO command works the exact same method other than that it uses the file named on the INTO stipulation in place of the short-term database and omits the action of copying the vacuumed database back over top of the original database. The VACUUM command may change the ROWIDs of entries in any tables that do not have an explicit INTEGER PRIMARY KEY.
Unfinalized SQL statements normally hold a checked out transaction open, so the VACUUM might fail if there are unfinalized SQL declarations on the very same connection. VACUUM (however not VACUUM INTO) is a write operation therefore if another database connection is holding a lock that avoids writes, then the VACUUM will stop working.
When auto_vacuum is allowed for a database free pages might be reclaimed after deleting information, triggering the file to diminish, without restoring the entire database using VACUUM. Nevertheless, utilizing auto_vacuum can cause additional database file fragmentation. And auto_vacuum does not compact partially filled pages of the database as VACUUM does.
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