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4a2f5533f3
The heuristic to avoid setting the VM during on-access pruning when
doing so would emit an extra FPI missed a few cases. First it missed
temp and unlogged tables. Those will never emit an FPI, so they can
always set the VM if the page is all-visible. It also missed that if
hint bits are not WAL-logged, setting only the VM passes REGBUF_NO_IMAGE
for an already WAL-logged heap page, forbidding a heap FPI in the WAL
record. A page that has never been WAL-logged still requires a heap FPI.
The third is more subtle: If the page is all-visible, the new prune xid
will be InvalidTransactionId. On-access pruning only executes when the
current pd_prune_xid is valid and visible. So, when on-access pruning
finds the page all-visible, it will always clear pd_prune_xid, modifying
the page.
Knowing this means we can set the VM without emitting an extra heap FPI
in more cases. When hint bits are WAL-logged, if the heap buffer is
clean, modifying pd_prune_xid will emit an FPI if one is required. There
is no reason to try to avoid an FPI by not setting the VM. So, set the
VM in this case. However, when the heap buffer is already dirty,
modifying pd_prune_xid can avoid an FPI; so if the page hasn't been
logged since the last checkpoint, setting it all-visible will emit an
extra heap page FPI. We will still avoid setting the VM in this case.
This is being backpatched to 19 because since 378a216187 pd_prune_xid
is set on insert, and if we execute a prune cycle and skip setting the
VM because of an incorrect heuristic, we have added new wasted work in
PG 19.
This commit adds some tests covering these cases. It also updates one of
the existing temp table tests to avoid exceeding the pin limit. Setting
the VM and FSM on-access when querying temp tables takes more local pins
and can run into the limit with fewer heap buffers pinned.
Reported-by: Melanie Plageman <melanieplageman@gmail.com>
Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Discussion: https://postgr.es/m/CAAKRu_amj7qLF4c=9ijd=708Fu2G8gg-2EqwBu=aCdAHU2sPHg@mail.gmail.com
Backpatch-through: 19
233 lines
8.4 KiB
PL/PgSQL
233 lines
8.4 KiB
PL/PgSQL
CREATE EXTENSION pg_visibility;
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CREATE EXTENSION pageinspect;
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--
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-- recently-dropped table
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--
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\set VERBOSITY sqlstate
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BEGIN;
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CREATE TABLE droppedtest (c int);
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SELECT 'droppedtest'::regclass::oid AS oid \gset
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SAVEPOINT q; DROP TABLE droppedtest; RELEASE q;
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SAVEPOINT q; SELECT * FROM pg_visibility_map(:oid); ROLLBACK TO q;
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-- ERROR: could not open relation with OID 16xxx
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SAVEPOINT q; SELECT 1; ROLLBACK TO q;
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SAVEPOINT q; SELECT 1; ROLLBACK TO q;
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SELECT pg_relation_size(:oid), pg_relation_filepath(:oid),
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has_table_privilege(:oid, 'SELECT');
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SELECT * FROM pg_visibility_map(:oid);
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-- ERROR: could not open relation with OID 16xxx
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ROLLBACK;
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\set VERBOSITY default
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--
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-- check that using the module's functions with unsupported relations will fail
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--
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-- partitioned tables (the parent ones) don't have visibility maps
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create table test_partitioned (a int) partition by list (a);
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-- these should all fail
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select pg_visibility('test_partitioned', 0);
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select pg_visibility_map('test_partitioned');
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select pg_visibility_map_summary('test_partitioned');
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select pg_check_frozen('test_partitioned');
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select pg_truncate_visibility_map('test_partitioned');
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create table test_partition partition of test_partitioned for values in (1);
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create index test_index on test_partition (a);
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-- indexes do not, so these all fail
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select pg_visibility('test_index', 0);
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select pg_visibility_map('test_index');
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select pg_visibility_map_summary('test_index');
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select pg_check_frozen('test_index');
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select pg_truncate_visibility_map('test_index');
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create view test_view as select 1;
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-- views do not have VMs, so these all fail
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select pg_visibility('test_view', 0);
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select pg_visibility_map('test_view');
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select pg_visibility_map_summary('test_view');
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select pg_check_frozen('test_view');
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select pg_truncate_visibility_map('test_view');
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create sequence test_sequence;
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-- sequences do not have VMs, so these all fail
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select pg_visibility('test_sequence', 0);
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select pg_visibility_map('test_sequence');
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select pg_visibility_map_summary('test_sequence');
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select pg_check_frozen('test_sequence');
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select pg_truncate_visibility_map('test_sequence');
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create foreign data wrapper dummy;
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create server dummy_server foreign data wrapper dummy;
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create foreign table test_foreign_table () server dummy_server;
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-- foreign tables do not have VMs, so these all fail
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select pg_visibility('test_foreign_table', 0);
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select pg_visibility_map('test_foreign_table');
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select pg_visibility_map_summary('test_foreign_table');
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select pg_check_frozen('test_foreign_table');
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select pg_truncate_visibility_map('test_foreign_table');
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-- check some of the allowed relkinds
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create table regular_table (a int, b text);
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alter table regular_table alter column b set storage external;
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insert into regular_table values (1, repeat('one', 1000)), (2, repeat('two', 1000));
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vacuum (disable_page_skipping) regular_table;
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select count(*) > 0 from pg_visibility('regular_table');
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select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
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truncate regular_table;
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select count(*) > 0 from pg_visibility('regular_table');
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select count(*) > 0 from pg_visibility((select reltoastrelid from pg_class where relname = 'regular_table'));
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create materialized view matview_visibility_test as select * from regular_table;
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vacuum (disable_page_skipping) matview_visibility_test;
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select count(*) > 0 from pg_visibility('matview_visibility_test');
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insert into regular_table values (1), (2);
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refresh materialized view matview_visibility_test;
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select count(*) > 0 from pg_visibility('matview_visibility_test');
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-- regular tables which are part of a partition *do* have visibility maps
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insert into test_partition values (1);
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vacuum (disable_page_skipping) test_partition;
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select count(*) > 0 from pg_visibility('test_partition', 0);
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select count(*) > 0 from pg_visibility_map('test_partition');
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select count(*) > 0 from pg_visibility_map_summary('test_partition');
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select * from pg_check_frozen('test_partition'); -- hopefully none
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select pg_truncate_visibility_map('test_partition');
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-- test the case where vacuum phase I does not need to modify the heap buffer
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-- and only needs to set the VM
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create temp table test_vac_unmodified_heap(a int);
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insert into test_vac_unmodified_heap values (1);
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vacuum (freeze) test_vac_unmodified_heap;
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select pg_visibility_map_summary('test_vac_unmodified_heap');
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-- the checkpoint cleans the buffer dirtied by freezing the sole tuple
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checkpoint;
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-- truncating the VM ensures that the next vacuum will need to set it
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select pg_truncate_visibility_map('test_vac_unmodified_heap');
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select pg_visibility_map_summary('test_vac_unmodified_heap');
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-- though the VM is truncated, the heap page-level visibility hint,
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-- PD_ALL_VISIBLE should still be set
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SELECT (flags & x'0004'::int) <> 0
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FROM page_header(get_raw_page('test_vac_unmodified_heap', 0));
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-- vacuum sets the VM
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vacuum test_vac_unmodified_heap;
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select pg_visibility_map_summary('test_vac_unmodified_heap');
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-- Test that on-access pruning during a read-only scan sets the VM. Temp
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-- tables are used because their visibility horizon depends only on this
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-- backend and no other process can pin their buffers, so the conditional
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-- cleanup lock needed for pruning is always available.
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create temp table test_on_access_vm(a int, b text) with (fillfactor = 90);
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insert into test_on_access_vm select g, repeat('x', 99)
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from generate_series(1, 500) g;
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-- HOT-update a few rows on every page. The new versions fit in the space
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-- reserved by the fillfactor, and afterwards each page has too little free
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-- space to escape on-access pruning.
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update test_on_access_vm set b = b where a % 20 = 0;
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select pg_visibility_map_summary('test_on_access_vm');
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-- A read-only scan that prunes tuples sets the VM
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select count(*) from test_on_access_vm;
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select pg_visibility_map_summary('test_on_access_vm');
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select * from pg_check_visible('test_on_access_vm');
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-- Test that a read-only scan of newly inserted data sets the VM
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create temp table test_on_access_vm_insert_only(a int, b text);
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insert into test_on_access_vm_insert_only select g, repeat('x', 99)
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from generate_series(1, 500) g;
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select pg_visibility_map_summary('test_on_access_vm_insert_only');
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select count(*) from test_on_access_vm_insert_only;
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select pg_visibility_map_summary('test_on_access_vm_insert_only');
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select * from pg_check_visible('test_on_access_vm_insert_only');
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-- Test that a scan of an UPDATE's target relation does not set the VM, even
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-- when no rows match.
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create temp table test_on_access_vm_modify(a int, b text) with (fillfactor = 90);
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insert into test_on_access_vm_modify select g, repeat('x', 99)
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from generate_series(1, 500) g;
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-- Create some dead rows for the next update's on-access pruning to clean up.
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-- We need to actually do pruning to exercise the right code path.
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update test_on_access_vm_modify set b = b where a % 20 = 0;
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-- This matches no rows, but scans every page as the query's result relation.
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update test_on_access_vm_modify set b = b where a = -1;
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select pg_visibility_map_summary('test_on_access_vm_modify');
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-- test copy freeze
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create table copyfreeze (a int, b char(1500));
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-- load all rows via COPY FREEZE and ensure that all pages are set all-visible
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-- and all-frozen.
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begin;
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truncate copyfreeze;
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copy copyfreeze from stdin freeze;
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1 '1'
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2 '2'
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3 '3'
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4 '4'
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5 '5'
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6 '6'
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\.
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commit;
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select * from pg_visibility_map('copyfreeze');
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select * from pg_check_frozen('copyfreeze');
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-- load half the rows via regular COPY and rest via COPY FREEZE. The pages
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-- which are touched by regular COPY must not be set all-visible/all-frozen. On
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-- the other hand, pages allocated by COPY FREEZE should be marked
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-- all-frozen/all-visible.
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begin;
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truncate copyfreeze;
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copy copyfreeze from stdin;
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1 '1'
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2 '2'
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3 '3'
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4 '4'
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5 '5'
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6 '6'
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\.
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copy copyfreeze from stdin freeze;
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7 '7'
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8 '8'
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9 '9'
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10 '10'
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11 '11'
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12 '12'
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\.
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commit;
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select * from pg_visibility_map('copyfreeze');
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select * from pg_check_frozen('copyfreeze');
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-- Try a mix of regular COPY and COPY FREEZE.
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begin;
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truncate copyfreeze;
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copy copyfreeze from stdin freeze;
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1 '1'
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2 '2'
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3 '3'
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4 '4'
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5 '5'
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\.
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copy copyfreeze from stdin;
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6 '6'
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\.
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copy copyfreeze from stdin freeze;
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7 '7'
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8 '8'
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9 '9'
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10 '10'
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11 '11'
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12 '12'
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\.
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commit;
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select * from pg_visibility_map('copyfreeze');
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select * from pg_check_frozen('copyfreeze');
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-- cleanup
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drop table test_partitioned;
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drop view test_view;
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drop sequence test_sequence;
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drop foreign table test_foreign_table;
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drop server dummy_server;
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drop foreign data wrapper dummy;
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drop materialized view matview_visibility_test;
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drop table regular_table;
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drop table copyfreeze;
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