Fix commit_ts for FrozenXid and BootstrapXid

Previously, requesting commit timestamp for transactions
FrozenTransactionId and BootstrapTransactionId resulted in an error.
But since those values can validly appear in committed tuples' Xmin,
this behavior is unhelpful and error prone: each caller would have to
special-case those values before requesting timestamp data for an Xid.
We already have a perfectly good interface for returning "the Xid you
requested is too old for us to have commit TS data for it", so let's use
that instead.

Backpatch to 9.5, where commit timestamps appeared.

Author: Craig Ringer
Discussion: https://www.postgresql.org/message-id/CAMsr+YFM5Q=+ry3mKvWEqRTxrB0iU3qUSRnS28nz6FJYtBwhJg@mail.gmail.com

diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
index 67c8bf3cd7deb44dae07bfd4f0d3a12ffa53be3f..3e045cda080e1be9d87ead47de081b8741ac2543 100644 (file)
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -288,11 +288,18 @@ TransactionIdGetCommitTsData(TransactionId xid, TimestampTz *ts,
        TransactionId oldestCommitTsXid;
        TransactionId newestCommitTsXid;
 
-       /* error if the given Xid doesn't normally commit */
-       if (!TransactionIdIsNormal(xid))
+       if (!TransactionIdIsValid(xid))
                ereport(ERROR,
                                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("cannot retrieve commit timestamp for transaction %u", xid)));
+       else if (!TransactionIdIsNormal(xid))
+       {
+               /* frozen and bootstrap xids are always committed far in the past */
+               *ts = 0;
+               if (nodeid)
+                       *nodeid = 0;
+               return false;
+       }
 
        LWLockAcquire(CommitTsLock, LW_SHARED);
 

diff --git a/src/test/modules/commit_ts/expected/commit_timestamp.out b/src/test/modules/commit_ts/expected/commit_timestamp.out
index 99f3322c42139977c871e82ac9cf493cc94a85e7..5b7783b58f3d8d4b1699e4236ec39daf82339e86 100644 (file)
--- a/src/test/modules/commit_ts/expected/commit_timestamp.out
+++ b/src/test/modules/commit_ts/expected/commit_timestamp.out
@@ -28,9 +28,17 @@ 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
+ pg_xact_commit_timestamp 
+--------------------------
+ 
+(1 row)
+
 SELECT pg_xact_commit_timestamp('2'::xid);
-ERROR:  cannot retrieve commit timestamp for transaction 2
+ pg_xact_commit_timestamp 
+--------------------------
+ 
+(1 row)
+
 SELECT x.xid::text::bigint > 0, x.timestamp > '-infinity'::timestamptz, x.timestamp <= now() FROM pg_last_committed_xact() x;
  ?column? | ?column? | ?column? 
 ----------+----------+----------

diff --git a/src/test/modules/commit_ts/expected/commit_timestamp_1.out b/src/test/modules/commit_ts/expected/commit_timestamp_1.out
index 2f1f41d209946b72f64d76352935446acb5e4d28..c10b0abc2b75d3630515a17492f1bcbbeab50c41 100644 (file)
--- a/src/test/modules/commit_ts/expected/commit_timestamp_1.out
+++ b/src/test/modules/commit_ts/expected/commit_timestamp_1.out
@@ -23,9 +23,17 @@ 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
+ pg_xact_commit_timestamp 
+--------------------------
+ 
+(1 row)
+
 SELECT pg_xact_commit_timestamp('2'::xid);
-ERROR:  cannot retrieve commit timestamp for transaction 2
+ pg_xact_commit_timestamp 
+--------------------------
+ 
+(1 row)
+
 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.

diff --git a/src/test/modules/commit_ts/t/004_restart.pl b/src/test/modules/commit_ts/t/004_restart.pl
index 900e9b7970855f214a2d97f5247c2cbb4497c94c..32be07c7414c499ddb23cd56403c8bb5fc2712fd 100644 (file)
--- a/src/test/modules/commit_ts/t/004_restart.pl
+++ b/src/test/modules/commit_ts/t/004_restart.pl
@@ -25,19 +25,13 @@ like(
 
 ($ret, $stdout, $stderr) =
   $node_master->psql('postgres', qq[SELECT pg_xact_commit_timestamp('1');]);
-is($ret, 3, 'getting ts of BootstrapTransactionId reports error');
-like(
-       $stderr,
-       qr/cannot retrieve commit timestamp for transaction/,
-       'expected error from BootstrapTransactionId');
+is($ret, 0, 'getting ts of BootstrapTransactionId succeeds');
+is($stdout, '', 'timestamp of BootstrapTransactionId is null');
 
 ($ret, $stdout, $stderr) =
   $node_master->psql('postgres', qq[SELECT pg_xact_commit_timestamp('2');]);
-is($ret, 3, 'getting ts of FrozenTransactionId reports error');
-like(
-       $stderr,
-       qr/cannot retrieve commit timestamp for transaction/,
-       'expected error from FrozenTransactionId');
+is($ret, 0, 'getting ts of FrozenTransactionId succeeds');
+is($stdout, '', 'timestamp of FrozenTransactionId is null');
 
 # Since FirstNormalTransactionId will've occurred during initdb, long before we
 # enabled commit timestamps, it'll be null since we have no cts data for it but