Keep track of transaction commit timestamps

Transactions can now set their commit timestamp directly as they commit,
or an external transaction commit timestamp can be fed from an outside
system using the new function TransactionTreeSetCommitTsData().  This
data is crash-safe, and truncated at Xid freeze point, same as pg_clog.

This module is disabled by default because it causes a performance hit,
but can be enabled in postgresql.conf requiring only a server restart.

A new test in src/test/modules is included.

Catalog version bumped due to the new subdirectory within PGDATA and a
couple of new SQL functions.

Authors: Álvaro Herrera and Petr Jelínek

Reviewed to varying degrees by Michael Paquier, Andres Freund, Robert
Haas, Amit Kapila, Fujii Masao, Jaime Casanova, Simon Riggs, Steven
Singer, Peter Eisentraut

src/test/modules/Makefile

@@ -5,6 +5,7 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 SUBDIRS = \
+		  commit_ts \
 		  worker_spi \
 		  dummy_seclabel \
 		  test_shm_mq \

src/test/modules/commit_ts/.gitignore

@@ -0,0 +1,4 @@
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/

src/test/modules/commit_ts/Makefile

@@ -0,0 +1,15 @@
+# src/test/modules/commit_ts/Makefile
+
+REGRESS = commit_timestamp
+REGRESS_OPTS = --temp-config=$(top_srcdir)/src/test/modules/commit_ts/commit_ts.conf
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/commit_ts
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

src/test/modules/commit_ts/commit_ts.conf

@@ -0,0 +1 @@
+track_commit_timestamp = on

src/test/modules/commit_ts/expected/commit_timestamp.out

@@ -0,0 +1,39 @@
+--
+-- Commit Timestamp
+--
+SHOW track_commit_timestamp;
+ track_commit_timestamp 
+------------------------
+ on
+(1 row)
+
+CREATE TABLE committs_test(id serial, ts timestamptz default now());
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+SELECT id,
+       pg_xact_commit_timestamp(xmin) >= ts,
+       pg_xact_commit_timestamp(xmin) < now(),
+       pg_xact_commit_timestamp(xmin) - ts < '60s' -- 60s should give a lot of reserve
+FROM committs_test
+ORDER BY id;
+ id | ?column? | ?column? | ?column? 
+----+----------+----------+----------
+  1 | t        | t        | t
+  2 | t        | t        | t
+  3 | t        | t        | t
+(3 rows)
+
+DROP TABLE committs_test;
+SELECT pg_xact_commit_timestamp('0'::xid);
+ERROR:  cannot retrieve commit timestamp for transaction 0
+SELECT pg_xact_commit_timestamp('1'::xid);
+ERROR:  cannot retrieve commit timestamp for transaction 1
+SELECT pg_xact_commit_timestamp('2'::xid);
+ERROR:  cannot retrieve commit timestamp for transaction 2
+SELECT x.xid::text::bigint > 0, x.timestamp > '-infinity'::timestamptz, x.timestamp < now() FROM pg_last_committed_xact() x;
+ ?column? | ?column? | ?column? 
+----------+----------+----------
+ t        | t        | t
+(1 row)
+

src/test/modules/commit_ts/expected/commit_timestamp_1.out

@@ -0,0 +1,34 @@
+--
+-- Commit Timestamp
+--
+SHOW track_commit_timestamp;
+ track_commit_timestamp 
+------------------------
+ off
+(1 row)
+
+CREATE TABLE committs_test(id serial, ts timestamptz default now());
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+SELECT id,
+       pg_xact_commit_timestamp(xmin) >= ts,
+       pg_xact_commit_timestamp(xmin) < now(),
+       pg_xact_commit_timestamp(xmin) - ts < '60s' -- 60s should give a lot of reserve
+FROM committs_test
+ORDER BY id;
+ERROR:  could not get commit timestamp data
+HINT:  Make sure the configuration parameter "track_commit_timestamp" is set.
+DROP TABLE committs_test;
+SELECT pg_xact_commit_timestamp('0'::xid);
+ERROR:  could not get commit timestamp data
+HINT:  Make sure the configuration parameter "track_commit_timestamp" is set.
+SELECT pg_xact_commit_timestamp('1'::xid);
+ERROR:  could not get commit timestamp data
+HINT:  Make sure the configuration parameter "track_commit_timestamp" is set.
+SELECT pg_xact_commit_timestamp('2'::xid);
+ERROR:  could not get commit timestamp data
+HINT:  Make sure the configuration parameter "track_commit_timestamp" is set.
+SELECT x.xid::text::bigint > 0, x.timestamp > '-infinity'::timestamptz, x.timestamp < now() FROM pg_last_committed_xact() x;
+ERROR:  could not get commit timestamp data
+HINT:  Make sure the configuration parameter "track_commit_timestamp" is set.

src/test/modules/commit_ts/sql/commit_timestamp.sql

@@ -0,0 +1,24 @@
+--
+-- Commit Timestamp
+--
+SHOW track_commit_timestamp;
+CREATE TABLE committs_test(id serial, ts timestamptz default now());
+
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+INSERT INTO committs_test DEFAULT VALUES;
+
+SELECT id,
+       pg_xact_commit_timestamp(xmin) >= ts,
+       pg_xact_commit_timestamp(xmin) < now(),
+       pg_xact_commit_timestamp(xmin) - ts < '60s' -- 60s should give a lot of reserve
+FROM committs_test
+ORDER BY id;
+
+DROP TABLE committs_test;
+
+SELECT pg_xact_commit_timestamp('0'::xid);
+SELECT pg_xact_commit_timestamp('1'::xid);
+SELECT pg_xact_commit_timestamp('2'::xid);
+
+SELECT x.xid::text::bigint > 0, x.timestamp > '-infinity'::timestamptz, x.timestamp < now() FROM pg_last_committed_xact() x;