On Sun, 29 Oct 2023 16:16:05 +0100 Peter J. Holzer wrote: >On 2023-10-29 09:21:46 -0400, pf@xxxxxxxxxxx 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). Am I correct to assume count(fieldname) would only load that column for counting? In other words: we should be specific (avoid "*") in general? >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 ║ >... Are there prerequisites for this query? Every (264) n_live_tup returned was zero... though, VERY fast.. :) >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. Thanks for sharing... We're learning fast... :) >> 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? It appears this is hard-coded [on/off only]; but I thought I saw the WB author post on this list recently... > hp >
