mirror of https://github.com/postgres/postgres
This option extracts (potentially decompressing) full-page images included in WAL records into a given target directory. These images are subject to the same filtering rules as the normal display of the WAL records, hence with --relation one can for example extract only the FPIs issued on the relation defined. By default, the records are printed or their stats computed (--stats), using --quiet would only save the images without any output generated. This is a tool aimed mostly for very experienced users, useful for fixing page-level corruption or just analyzing the past state of a page, and there were no easy way to do that with the in-core tools up to now when looking at WAL. Each block is saved in a separate file, to ease their manipulation, with the file respecting <lsn>.<ts>.<db>.<rel>.<blk>_<fork> with as format. For instance, 00000000-010000C0.1663.1.6117.123_main refers to: - WAL record LSN in hexa format (00000000-010000C0). - Tablespace OID (1663). - Database OID (1). - Relfilenode (6117). - Block number (123). - Fork name of the file this block came from (_main). Author: David Christensen Reviewed-by: Sho Kato, Justin Pryzby, Bharath Rupireddy, Matthias van de Meent Discussion: https://postgr.es/m/CAOxo6XKjQb2bMSBRpePf3ZpzfNTwjQUc4Tafh21=jzjX6bX8CA@mail.gmail.compull/111/head
Michael Paquier
3 years ago
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# Copyright (c) 2022, PostgreSQL Global Development Group |
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use strict; |
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use warnings; |
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use File::Basename; |
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use PostgreSQL::Test::Cluster; |
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use PostgreSQL::Test::RecursiveCopy; |
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use PostgreSQL::Test::Utils; |
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use Test::More; |
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my ($blocksize, $walfile_name); |
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# Function to extract the LSN from the given block structure |
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sub get_block_lsn |
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{ |
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my $path = shift; |
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my $blocksize = shift; |
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my $block; |
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open my $fh, '<', $path or die "couldn't open file: $path\n"; |
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die "could not read block\n" |
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if $blocksize != read($fh, $block, $blocksize); |
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my ($lsn_hi, $lsn_lo) = unpack('LL', $block); |
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$lsn_hi = sprintf('%08X', $lsn_hi); |
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$lsn_lo = sprintf('%08X', $lsn_lo); |
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return ($lsn_hi, $lsn_lo); |
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} |
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my $node = PostgreSQL::Test::Cluster->new('main'); |
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$node->init; |
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$node->append_conf( |
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'postgresql.conf', q{ |
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wal_level = 'replica' |
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max_wal_senders = 4 |
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}); |
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$node->start; |
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# Generate data/WAL to examine that will have full pages in them. |
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$node->safe_psql( |
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'postgres', |
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"SELECT 'init' FROM pg_create_physical_replication_slot('regress_pg_waldump_slot', true, false); |
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CREATE TABLE test_table AS SELECT generate_series(1,100) a; |
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-- Force FPWs on the next writes. |
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CHECKPOINT; |
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UPDATE test_table SET a = a + 1; |
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"); |
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($walfile_name, $blocksize) = split '\|' => $node->safe_psql('postgres', |
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"SELECT pg_walfile_name(pg_switch_wal()), current_setting('block_size')"); |
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# Get the relation node, etc for the new table |
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my $relation = $node->safe_psql( |
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'postgres', |
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q{SELECT format( |
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'%s/%s/%s', |
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CASE WHEN reltablespace = 0 THEN dattablespace ELSE reltablespace END, |
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pg_database.oid, |
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pg_relation_filenode(pg_class.oid)) |
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FROM pg_class, pg_database |
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WHERE relname = 'test_table' AND |
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datname = current_database()} |
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); |
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my $walfile = $node->data_dir . '/pg_wal/' . $walfile_name; |
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my $tmp_folder = PostgreSQL::Test::Utils::tempdir; |
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ok(-f $walfile, "Got a WAL file"); |
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$node->command_ok( |
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[ |
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'pg_waldump', '--quiet', |
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'--save-fullpage', "$tmp_folder/raw", |
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'--relation', $relation, |
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$walfile |
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]); |
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# This regexp will match filenames formatted as: |
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# XXXXXXXX-XXXXXXXX.DBOID.TLOID.NODEOID.dd_fork with the components being: |
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# - WAL LSN in hex format, |
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# - Tablespace OID (0 for global) |
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# - Database OID. |
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# - Relfilenode. |
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# - Block number. |
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# - Fork this block came from (vm, init, fsm, or main). |
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my $file_re = |
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qr/^([0-9A-F]{8})-([0-9A-F]{8})[.][0-9]+[.][0-9]+[.][0-9]+[.][0-9]+(?:_vm|_init|_fsm|_main)?$/; |
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my $file_count = 0; |
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# Verify filename format matches --save-fullpage. |
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for my $fullpath (glob "$tmp_folder/raw/*") |
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{ |
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my $file = File::Basename::basename($fullpath); |
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like($file, $file_re, "verify filename format for file $file"); |
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$file_count++; |
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my ($hi_lsn_fn, $lo_lsn_fn) = ($file =~ $file_re); |
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my ($hi_lsn_bk, $lo_lsn_bk) = get_block_lsn($fullpath, $blocksize); |
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# The LSN on the block comes before the file's LSN. |
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ok( $hi_lsn_fn . $lo_lsn_fn gt $hi_lsn_bk . $lo_lsn_bk, |
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'LSN stored in the file precedes the one stored in the block'); |
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} |
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ok($file_count > 0, 'verify that at least one block has been saved'); |
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done_testing(); |
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Reference in new issue