Re: pg_total_relation_size accuracy guarantee

Source is good enough in my case and I planned to grep it anyway, so thanks for saving my time! 2017-11-24 10:15 GMT+03:00 Laurenz Albe : > Nikita wrote: > > 1. pg_total_relation_size return predictable approximately correct table > size (apart from some preallocation) without subsequent > VACUUM/ANALYZE/anything call as long as I don't DELETE/UPDATE rows; > > > > 2. DROP/TRUNCATE table reclaim disc space without subsequent VACUUM; > > > > These assumptions are correct? Is it fixed in doc if so? > > Sort of, if you consider the source as documentation. > > Ad pg_total_relation_size: > > See the function definition in backend/utils/adt/dbsize.c and > the functions that it calls, especially "calculate_relation_size": > > PostgreSQL uses the stat(2) system call to determine the actual > size of the files on disk. > > Ad TRUNCATE (from backend/commands/tablecmds.c): > > /* > * Need the full transaction-safe pushups. > * > * Create a new empty storage file for the relation, and assign it > * as the relfilenode value. The old storage file is scheduled for > * deletion at commit. > */ > > Yours, > Laurenz Albe >