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 <laurenz(dot)albe(at)cybertec(dot)at>:

> 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
>