Re: [SOLVED?] Re: Disk wait problem... not hardware...

On 2023-10-29 09:21:46 -0400, pf(at)pfortin(dot)com wrote:
> These are all static tables. Does PG maintain a table row count so as to
> avoid having to count each time?

No. To count the rows in a table, Postgres has to actually read the
whole table (or an index, if a suitable index (e.g. a primary key)
exists).

However, the table statistics contain an estimate for the number of
rows:

hjp=> select schemaname, relname, n_live_tup from pg_stat_user_tables order by 3 desc;
╔════════════╤═══════════════════════════╤════════════╗
║ schemaname │ relname │ n_live_tup ║
╟────────────┼───────────────────────────┼────────────╢
║ public │ ncvhis_2016_12_03 │ 9999977 ║
║ public │ random_test │ 1000000 ║
║ public │ beislindex │ 351 ║
║ public │ delivery │ 6 ║
...

This is an estimate, not the actual count, so it might be wrong
(sometimes very wrong), but accessing it is fast and it might be good
enough for your purposes.

> WB is setup to:
> * autoload table row count
> * autoload table data (restricted with LIMIT)

Maybe WB can be set up to get n_live_tup instead of the real row count?

hp

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_ | Peter J. Holzer | Story must make more sense than reality.
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