On 2/13/17, Scott Hess <sh...@google.com> wrote: > > Below is a patch which implements [PRAGMA auto_vacuum_slack_pages = N]. > This setting allows client code to signal that auto_vacuum can leave pages > on the freelist until releasing them would allow a db size change.
This makes me want to ask: Is anybody still using auto_vacuum? And if they are, should they be? Auto-vacuum was invented way back in 2004, for Motorola, who at the time was the worlds leading manufacturer of mobile phones. This was during the heyday of flip-phones, before iPhone or Android. The devices had very little flash memory - total storage capacity was measured in megabytes rather than gigabytes. If storage ran low, Motorola wanted to be able to VACUUM the SQLite databases to make them smaller. The problem there is VACUUM requires nearly 2x the size of the original database in temp storage, so if you are already low on space, VACUUM probably won't work. The solution was auto-vacuum, which keeps the databases at near their minimum size at all times, at the cost of some extra database fragmentation, more I/O, and reduced performance. Fast foward 13 years (how long is that in internet-years?) and the situation has changed. Does anybody really care anymore that a database file might have a few dozen pages on its freelist? Or if they do care, does anybody lack the temp space sufficient to run a real VACUUM? My impression is that these days people just want the database to run fast and with a minimum of I/O and are not overly concerned with a few extra freelist pages, which means that auto-vacuum should remain turned off. Scott: The motivation for your patch seem to be to get auto-vacuum to run a little faster. But if performance is your goal, why not just turn auto-vacuum off? Or, failing that, set it to INCREMENTAL and then run "PRAGMA incremental_vacuum" when "PRAGMA freelist_count" reaches some threshold? -- D. Richard Hipp d...@sqlite.org _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
