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Add contrib/pg_logicalinspect.
This module provides SQL functions that allow to inspect logical decoding components. It currently allows to inspect the contents of serialized logical snapshots of a running database cluster, which is useful for debugging or educational purposes. Author: Bertrand Drouvot Reviewed-by: Amit Kapila, Shveta Malik, Peter Smith, Peter Eisentraut Reviewed-by: David G. Johnston Discussion: https://postgr.es/m/ZscuZ92uGh3wm4tW%40ip-10-97-1-34.eu-west-3.compute.internal
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‎contrib/Makefile

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@@ -32,6 +32,7 @@ SUBDIRS = \
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passwordcheck \
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pg_buffercache \
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pg_freespacemap \
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pg_logicalinspect \
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pg_prewarm \
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pg_stat_statements \
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pg_surgery \

‎contrib/meson.build

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@@ -46,6 +46,7 @@ subdir('passwordcheck')
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subdir('pg_buffercache')
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subdir('pgcrypto')
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subdir('pg_freespacemap')
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subdir('pg_logicalinspect')
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subdir('pg_prewarm')
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subdir('pgrowlocks')
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subdir('pg_stat_statements')

‎contrib/pg_logicalinspect/.gitignore

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# Generated subdirectories
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/log/
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/results/
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/output_iso/
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/tmp_check/
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/tmp_check_iso/

‎contrib/pg_logicalinspect/Makefile

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# contrib/pg_logicalinspect/Makefile
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MODULE_big = pg_logicalinspect
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OBJS = \
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$(WIN32RES) \
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pg_logicalinspect.o
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PGFILEDESC = "pg_logicalinspect - functions to inspect logical decoding components"
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EXTENSION = pg_logicalinspect
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DATA = pg_logicalinspect--1.0.sql
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EXTRA_INSTALL = contrib/test_decoding
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ISOLATION = logical_inspect
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ISOLATION_OPTS = --temp-config $(top_srcdir)/contrib/pg_logicalinspect/logicalinspect.conf
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# Disabled because these tests require "wal_level=logical", which
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# some installcheck users do not have (e.g. buildfarm clients).
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NO_INSTALLCHECK = 1
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ifdef USE_PGXS
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PG_CONFIG = pg_config
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PGXS := $(shell $(PG_CONFIG) --pgxs)
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include $(PGXS)
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else
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subdir = contrib/pg_logicalinspect
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top_builddir = ../..
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include $(top_builddir)/src/Makefile.global
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include $(top_srcdir)/contrib/contrib-global.mk
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endif

‎contrib/pg_logicalinspect/expected/logical_inspect.out

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Parsed test spec with 2 sessions
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starting permutation: s0_init s0_begin s0_savepoint s0_truncate s1_checkpoint s1_get_changes s0_commit s0_begin s0_insert s1_checkpoint s1_get_changes s0_commit s1_get_changes s1_get_logical_snapshot_info s1_get_logical_snapshot_meta
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step s0_init: SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
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?column?
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--------
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init
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(1 row)
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step s0_begin: BEGIN;
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step s0_savepoint: SAVEPOINT sp1;
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step s0_truncate: TRUNCATE tbl1;
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step s1_checkpoint: CHECKPOINT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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----
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(0 rows)
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step s0_commit: COMMIT;
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step s0_begin: BEGIN;
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step s0_insert: INSERT INTO tbl1 VALUES (1);
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step s1_checkpoint: CHECKPOINT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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---------------------------------------
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BEGIN
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table public.tbl1: TRUNCATE: (no-flags)
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COMMIT
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(3 rows)
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step s0_commit: COMMIT;
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step s1_get_changes: SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
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data
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-------------------------------------------------------------
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BEGIN
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table public.tbl1: INSERT: val1[integer]:1 val2[integer]:null
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COMMIT
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(3 rows)
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step s1_get_logical_snapshot_info: SELECT info.state, info.catchange_count, array_length(info.catchange_xip,1) AS catchange_array_length, info.committed_count, array_length(info.committed_xip,1) AS committed_array_length FROM pg_ls_logicalsnapdir(), pg_get_logical_snapshot_info(name) AS info ORDER BY 2;
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state |catchange_count|catchange_array_length|committed_count|committed_array_length
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----------+---------------+----------------------+---------------+----------------------
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consistent| 0| | 2| 2
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consistent| 2| 2| 0|
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(2 rows)
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step s1_get_logical_snapshot_meta: SELECT COUNT(meta.*) from pg_ls_logicalsnapdir(), pg_get_logical_snapshot_meta(name) as meta;
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count
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-----
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2
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(1 row)
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‎contrib/pg_logicalinspect/logicalinspect.conf

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wal_level = logical

‎contrib/pg_logicalinspect/meson.build

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# Copyright (c) 2024, PostgreSQL Global Development Group
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pg_logicalinspect_sources = files('pg_logicalinspect.c')
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if host_system == 'windows'
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pg_logicalinspect_sources += rc_lib_gen.process(win32ver_rc, extra_args: [
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'--NAME', 'pg_logicalinspect',
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'--FILEDESC', 'pg_logicalinspect - functions to inspect logical decoding components',])
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endif
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pg_logicalinspect = shared_module('pg_logicalinspect',
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pg_logicalinspect_sources,
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kwargs: contrib_mod_args + {
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'dependencies': contrib_mod_args['dependencies'],
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},
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)
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contrib_targets += pg_logicalinspect
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install_data(
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'pg_logicalinspect.control',
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'pg_logicalinspect--1.0.sql',
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kwargs: contrib_data_args,
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)
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tests += {
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'name': 'pg_logicalinspect',
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'sd': meson.current_source_dir(),
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'bd': meson.current_build_dir(),
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'isolation': {
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'specs': [
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'logical_inspect',
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],
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'regress_args': [
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'--temp-config', files('logicalinspect.conf'),
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],
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# see above
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'runningcheck': false,
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},
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}

‎contrib/pg_logicalinspect/pg_logicalinspect--1.0.sql

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/* contrib/pg_logicalinspect/pg_logicalinspect--1.0.sql */
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-- complain if script is sourced in psql, rather than via CREATE EXTENSION
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\echo Use "CREATE EXTENSION pg_logicalinspect" to load this file. \quit
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--
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-- pg_get_logical_snapshot_meta()
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--
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CREATE FUNCTION pg_get_logical_snapshot_meta(IN filename text,
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OUT magic int4,
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OUT checksum int8,
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OUT version int4
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)
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AS 'MODULE_PATHNAME', 'pg_get_logical_snapshot_meta'
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LANGUAGE C STRICT PARALLEL SAFE;
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REVOKE EXECUTE ON FUNCTION pg_get_logical_snapshot_meta(text) FROM PUBLIC;
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GRANT EXECUTE ON FUNCTION pg_get_logical_snapshot_meta(text) TO pg_read_server_files;
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--
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-- pg_get_logical_snapshot_info()
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--
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CREATE FUNCTION pg_get_logical_snapshot_info(IN filename text,
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OUT state text,
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OUT xmin xid,
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OUT xmax xid,
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OUT start_decoding_at pg_lsn,
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OUT two_phase_at pg_lsn,
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OUT initial_xmin_horizon xid,
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OUT building_full_snapshot boolean,
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OUT in_slot_creation boolean,
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OUT last_serialized_snapshot pg_lsn,
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OUT next_phase_at xid,
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OUT committed_count int4,
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OUT committed_xip xid[],
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OUT catchange_count int4,
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OUT catchange_xip xid[]
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)
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AS 'MODULE_PATHNAME', 'pg_get_logical_snapshot_info'
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LANGUAGE C STRICT PARALLEL SAFE;
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REVOKE EXECUTE ON FUNCTION pg_get_logical_snapshot_info(text) FROM PUBLIC;
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GRANT EXECUTE ON FUNCTION pg_get_logical_snapshot_info(text) TO pg_read_server_files;

‎contrib/pg_logicalinspect/pg_logicalinspect.c

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/*-------------------------------------------------------------------------
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*
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* pg_logicalinspect.c
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* Functions to inspect contents of PostgreSQL logical snapshots
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*
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* Copyright (c) 2024, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/pg_logicalinspect/pg_logicalinspect.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "funcapi.h"
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#include "replication/snapbuild_internal.h"
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#include "utils/array.h"
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#include "utils/builtins.h"
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#include "utils/pg_lsn.h"
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PG_MODULE_MAGIC;
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PG_FUNCTION_INFO_V1(pg_get_logical_snapshot_meta);
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PG_FUNCTION_INFO_V1(pg_get_logical_snapshot_info);
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/* Return the description of SnapBuildState */
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static const char *
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get_snapbuild_state_desc(SnapBuildState state)
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{
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const char *stateDesc = "unknown state";
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switch (state)
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{
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case SNAPBUILD_START:
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stateDesc = "start";
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break;
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case SNAPBUILD_BUILDING_SNAPSHOT:
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stateDesc = "building";
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break;
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case SNAPBUILD_FULL_SNAPSHOT:
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stateDesc = "full";
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break;
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case SNAPBUILD_CONSISTENT:
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stateDesc = "consistent";
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break;
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}
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return stateDesc;
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}
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/*
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* Retrieve the logical snapshot file metadata.
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*/
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Datum
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pg_get_logical_snapshot_meta(PG_FUNCTION_ARGS)
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{
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#define PG_GET_LOGICAL_SNAPSHOT_META_COLS 3
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SnapBuildOnDisk ondisk;
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HeapTuple tuple;
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Datum values[PG_GET_LOGICAL_SNAPSHOT_META_COLS] = {0};
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bool nulls[PG_GET_LOGICAL_SNAPSHOT_META_COLS] = {0};
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TupleDesc tupdesc;
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char path[MAXPGPATH];
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int i = 0;
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text *filename_t = PG_GETARG_TEXT_PP(0);
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/* Build a tuple descriptor for our result type */
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if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
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elog(ERROR, "return type must be a row type");
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sprintf(path, "%s/%s",
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PG_LOGICAL_SNAPSHOTS_DIR,
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text_to_cstring(filename_t));
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/* Validate and restore the snapshot to 'ondisk' */
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SnapBuildRestoreSnapshot(&ondisk, path, CurrentMemoryContext, false);
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values[i++] = UInt32GetDatum(ondisk.magic);
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values[i++] = Int64GetDatum((int64) ondisk.checksum);
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values[i++] = UInt32GetDatum(ondisk.version);
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Assert(i == PG_GET_LOGICAL_SNAPSHOT_META_COLS);
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tuple = heap_form_tuple(tupdesc, values, nulls);
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PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
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#undef PG_GET_LOGICAL_SNAPSHOT_META_COLS
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}
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Datum
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pg_get_logical_snapshot_info(PG_FUNCTION_ARGS)
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{
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#define PG_GET_LOGICAL_SNAPSHOT_INFO_COLS 14
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SnapBuildOnDisk ondisk;
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HeapTuple tuple;
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Datum values[PG_GET_LOGICAL_SNAPSHOT_INFO_COLS] = {0};
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bool nulls[PG_GET_LOGICAL_SNAPSHOT_INFO_COLS] = {0};
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TupleDesc tupdesc;
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char path[MAXPGPATH];
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int i = 0;
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text *filename_t = PG_GETARG_TEXT_PP(0);
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/* Build a tuple descriptor for our result type */
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if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
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elog(ERROR, "return type must be a row type");
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sprintf(path, "%s/%s",
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PG_LOGICAL_SNAPSHOTS_DIR,
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text_to_cstring(filename_t));
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/* Validate and restore the snapshot to 'ondisk' */
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SnapBuildRestoreSnapshot(&ondisk, path, CurrentMemoryContext, false);
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values[i++] = CStringGetTextDatum(get_snapbuild_state_desc(ondisk.builder.state));
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values[i++] = TransactionIdGetDatum(ondisk.builder.xmin);
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values[i++] = TransactionIdGetDatum(ondisk.builder.xmax);
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values[i++] = LSNGetDatum(ondisk.builder.start_decoding_at);
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values[i++] = LSNGetDatum(ondisk.builder.two_phase_at);
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values[i++] = TransactionIdGetDatum(ondisk.builder.initial_xmin_horizon);
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values[i++] = BoolGetDatum(ondisk.builder.building_full_snapshot);
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values[i++] = BoolGetDatum(ondisk.builder.in_slot_creation);
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values[i++] = LSNGetDatum(ondisk.builder.last_serialized_snapshot);
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values[i++] = TransactionIdGetDatum(ondisk.builder.next_phase_at);
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values[i++] = UInt32GetDatum(ondisk.builder.committed.xcnt);
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if (ondisk.builder.committed.xcnt > 0)
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{
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Datum *arrayelems;
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arrayelems = (Datum *) palloc(ondisk.builder.committed.xcnt * sizeof(Datum));
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for (int j = 0; j < ondisk.builder.committed.xcnt; j++)
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arrayelems[j] = TransactionIdGetDatum(ondisk.builder.committed.xip[j]);
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values[i++] = PointerGetDatum(construct_array_builtin(arrayelems,
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ondisk.builder.committed.xcnt,
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XIDOID));
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}
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else
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nulls[i++] = true;
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values[i++] = UInt32GetDatum(ondisk.builder.catchange.xcnt);
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if (ondisk.builder.catchange.xcnt > 0)
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{
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Datum *arrayelems;
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arrayelems = (Datum *) palloc(ondisk.builder.catchange.xcnt * sizeof(Datum));
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for (int j = 0; j < ondisk.builder.catchange.xcnt; j++)
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arrayelems[j] = TransactionIdGetDatum(ondisk.builder.catchange.xip[j]);
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values[i++] = PointerGetDatum(construct_array_builtin(arrayelems,
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ondisk.builder.catchange.xcnt,
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XIDOID));
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}
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else
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nulls[i++] = true;
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Assert(i == PG_GET_LOGICAL_SNAPSHOT_INFO_COLS);
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tuple = heap_form_tuple(tupdesc, values, nulls);
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PG_RETURN_DATUM(HeapTupleGetDatum(tuple));
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#undef PG_GET_LOGICAL_SNAPSHOT_INFO_COLS
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}

‎contrib/pg_logicalinspect/pg_logicalinspect.control

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# pg_logicalinspect extension
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comment = 'functions to inspect logical decoding components'
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default_version = '1.0'
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module_pathname = '$libdir/pg_logicalinspect'
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relocatable = true

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