问题
I deleted many records from my table but the DB size (Firebird) left the same. How do I decrease it?
I am looking for something similar to vacuum in PostgreS.
回答1:
This is one of many pains of firebird. Best and only effective and right way to do this - backup/restore your database using gbak
回答2:
Firebird will occasionally run a sweep to remove the records from indexes etc., and regain the space for other use. In other words, as soon as the sweep has run, you will have the same performance as if the database file was smaller. You can enforce an immediate sweep, if that is what you are trying to do.
However, the size of the actual database will not shrink, no matter what, except if you do a backup and restore. If size is a problem, use the -USE_ALL_SPACE parameter for gbak, it will prevent that space is being reserved for future records, which will yield a smaller database.
回答3:
From the official faq
Many users wonder why they don't get their disk space back when they delete a lot of records from database.
The reason is that it is an expensive operation, it would require a lot of disk writes and memory - just like doing refragmentation of hard disk partition. The parts of database (pages) that were used by such data are marked as empty and Firebird will reuse them next time it needs to write new data.
If disk space is critical for you, you can get the space back by doing backup and then restore. Since you're doing the backup to restore right away, it's wise to use the "inhibit garbage collection" or "don't use garbage collection" switch (-G in gbak), which will make backup go A LOT FASTER. Garbage collection is used to clean up your database, and as it is a maintenance task, it's often done together with backup (as backup has to go throught entire database anyway). However, you're soon going to ditch that database file, and there's no need to clean it up.
来源：https://stackoverflow.com/questions/1662431/how-do-i-optimize-table-after-delete-many-records