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b43f7c117e
This reverts much of commit f03a9ca436
,
but leaves the relpages/reltuples probe in select_parallel.sql.
The pg_stat_all_tables probes are unstable enough to be annoying,
and it no longer seems likely that they will teach us anything more
about the underlying problem. I'd still like some more confirmation
though that the observed plan instability is caused by VACUUM leaving
relpages/reltuples as zero for one of these tables.
Discussion: https://postgr.es/m/CA+hUKG+0CxrKRWRMf5ymN3gm+BECHna2B-q1w8onKBep4HasUw@mail.gmail.com
180 lines
6.3 KiB
PL/PgSQL
180 lines
6.3 KiB
PL/PgSQL
--
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-- Test Statistics Collector
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--
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-- Must be run after tenk2 has been created (by create_table),
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-- populated (by create_misc) and indexed (by create_index).
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--
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-- conditio sine qua non
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SHOW track_counts; -- must be on
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-- ensure that both seqscan and indexscan plans are allowed
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SET enable_seqscan TO on;
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SET enable_indexscan TO on;
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-- for the moment, we don't want index-only scans here
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SET enable_indexonlyscan TO off;
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-- save counters
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CREATE TABLE prevstats AS
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SELECT t.seq_scan, t.seq_tup_read, t.idx_scan, t.idx_tup_fetch,
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(b.heap_blks_read + b.heap_blks_hit) AS heap_blks,
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(b.idx_blks_read + b.idx_blks_hit) AS idx_blks,
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pg_stat_get_snapshot_timestamp() as snap_ts
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FROM pg_catalog.pg_stat_user_tables AS t,
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pg_catalog.pg_statio_user_tables AS b
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WHERE t.relname='tenk2' AND b.relname='tenk2';
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-- function to wait for counters to advance
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create function wait_for_stats() returns void as $$
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declare
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start_time timestamptz := clock_timestamp();
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updated1 bool;
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updated2 bool;
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updated3 bool;
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updated4 bool;
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begin
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-- we don't want to wait forever; loop will exit after 30 seconds
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for i in 1 .. 300 loop
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-- With parallel query, the seqscan and indexscan on tenk2 might be done
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-- in parallel worker processes, which will send their stats counters
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-- asynchronously to what our own session does. So we must check for
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-- those counts to be registered separately from the update counts.
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-- check to see if seqscan has been sensed
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SELECT (st.seq_scan >= pr.seq_scan + 1) INTO updated1
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FROM pg_stat_user_tables AS st, pg_class AS cl, prevstats AS pr
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WHERE st.relname='tenk2' AND cl.relname='tenk2';
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-- check to see if indexscan has been sensed
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SELECT (st.idx_scan >= pr.idx_scan + 1) INTO updated2
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FROM pg_stat_user_tables AS st, pg_class AS cl, prevstats AS pr
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WHERE st.relname='tenk2' AND cl.relname='tenk2';
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-- check to see if all updates have been sensed
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SELECT (n_tup_ins > 0) INTO updated3
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FROM pg_stat_user_tables WHERE relname='trunc_stats_test4';
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-- We must also check explicitly that pg_stat_get_snapshot_timestamp has
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-- advanced, because that comes from the global stats file which might
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-- be older than the per-DB stats file we got the other values from.
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SELECT (pr.snap_ts < pg_stat_get_snapshot_timestamp()) INTO updated4
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FROM prevstats AS pr;
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exit when updated1 and updated2 and updated3 and updated4;
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-- wait a little
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perform pg_sleep_for('100 milliseconds');
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-- reset stats snapshot so we can test again
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perform pg_stat_clear_snapshot();
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end loop;
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-- report time waited in postmaster log (where it won't change test output)
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raise log 'wait_for_stats delayed % seconds',
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extract(epoch from clock_timestamp() - start_time);
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end
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$$ language plpgsql;
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-- test effects of TRUNCATE on n_live_tup/n_dead_tup counters
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CREATE TABLE trunc_stats_test(id serial);
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CREATE TABLE trunc_stats_test1(id serial, stuff text);
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CREATE TABLE trunc_stats_test2(id serial);
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CREATE TABLE trunc_stats_test3(id serial, stuff text);
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CREATE TABLE trunc_stats_test4(id serial);
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-- check that n_live_tup is reset to 0 after truncate
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INSERT INTO trunc_stats_test DEFAULT VALUES;
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INSERT INTO trunc_stats_test DEFAULT VALUES;
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INSERT INTO trunc_stats_test DEFAULT VALUES;
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TRUNCATE trunc_stats_test;
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-- test involving a truncate in a transaction; 4 ins but only 1 live
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INSERT INTO trunc_stats_test1 DEFAULT VALUES;
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INSERT INTO trunc_stats_test1 DEFAULT VALUES;
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INSERT INTO trunc_stats_test1 DEFAULT VALUES;
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UPDATE trunc_stats_test1 SET id = id + 10 WHERE id IN (1, 2);
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DELETE FROM trunc_stats_test1 WHERE id = 3;
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BEGIN;
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UPDATE trunc_stats_test1 SET id = id + 100;
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TRUNCATE trunc_stats_test1;
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INSERT INTO trunc_stats_test1 DEFAULT VALUES;
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COMMIT;
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-- use a savepoint: 1 insert, 1 live
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BEGIN;
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INSERT INTO trunc_stats_test2 DEFAULT VALUES;
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INSERT INTO trunc_stats_test2 DEFAULT VALUES;
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SAVEPOINT p1;
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INSERT INTO trunc_stats_test2 DEFAULT VALUES;
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TRUNCATE trunc_stats_test2;
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INSERT INTO trunc_stats_test2 DEFAULT VALUES;
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RELEASE SAVEPOINT p1;
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COMMIT;
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-- rollback a savepoint: this should count 4 inserts and have 2
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-- live tuples after commit (and 2 dead ones due to aborted subxact)
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BEGIN;
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INSERT INTO trunc_stats_test3 DEFAULT VALUES;
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INSERT INTO trunc_stats_test3 DEFAULT VALUES;
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SAVEPOINT p1;
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INSERT INTO trunc_stats_test3 DEFAULT VALUES;
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INSERT INTO trunc_stats_test3 DEFAULT VALUES;
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TRUNCATE trunc_stats_test3;
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INSERT INTO trunc_stats_test3 DEFAULT VALUES;
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ROLLBACK TO SAVEPOINT p1;
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COMMIT;
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-- rollback a truncate: this should count 2 inserts and produce 2 dead tuples
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BEGIN;
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INSERT INTO trunc_stats_test4 DEFAULT VALUES;
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INSERT INTO trunc_stats_test4 DEFAULT VALUES;
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TRUNCATE trunc_stats_test4;
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INSERT INTO trunc_stats_test4 DEFAULT VALUES;
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ROLLBACK;
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-- do a seqscan
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SELECT count(*) FROM tenk2;
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-- do an indexscan
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-- make sure it is not a bitmap scan, which might skip fetching heap tuples
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SET enable_bitmapscan TO off;
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SELECT count(*) FROM tenk2 WHERE unique1 = 1;
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RESET enable_bitmapscan;
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-- We can't just call wait_for_stats() at this point, because we only
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-- transmit stats when the session goes idle, and we probably didn't
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-- transmit the last couple of counts yet thanks to the rate-limiting logic
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-- in pgstat_report_stat(). But instead of waiting for the rate limiter's
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-- timeout to elapse, let's just start a new session. The old one will
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-- then send its stats before dying.
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\c -
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-- wait for stats collector to update
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SELECT wait_for_stats();
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-- check effects
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SELECT relname, n_tup_ins, n_tup_upd, n_tup_del, n_live_tup, n_dead_tup
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FROM pg_stat_user_tables
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WHERE relname like 'trunc_stats_test%' order by relname;
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SELECT st.seq_scan >= pr.seq_scan + 1,
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st.seq_tup_read >= pr.seq_tup_read + cl.reltuples,
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st.idx_scan >= pr.idx_scan + 1,
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st.idx_tup_fetch >= pr.idx_tup_fetch + 1
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FROM pg_stat_user_tables AS st, pg_class AS cl, prevstats AS pr
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WHERE st.relname='tenk2' AND cl.relname='tenk2';
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SELECT st.heap_blks_read + st.heap_blks_hit >= pr.heap_blks + cl.relpages,
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st.idx_blks_read + st.idx_blks_hit >= pr.idx_blks + 1
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FROM pg_statio_user_tables AS st, pg_class AS cl, prevstats AS pr
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WHERE st.relname='tenk2' AND cl.relname='tenk2';
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SELECT pr.snap_ts < pg_stat_get_snapshot_timestamp() as snapshot_newer
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FROM prevstats AS pr;
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DROP TABLE trunc_stats_test, trunc_stats_test1, trunc_stats_test2, trunc_stats_test3, trunc_stats_test4;
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DROP TABLE prevstats;
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-- End of Stats Test
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