Fix portability issues with parsing of recovery_target_xid

The parsing of this parameter has been using strtoul(), which is not
portable across platforms.  On most Unix platforms, unsigned long has a
size of 64 bits, while on Windows it is 32 bits.  It is common in
recovery scenarios to rely on the output of txid_current() or even the
newer pg_current_xact_id() to get a transaction ID for setting up
recovery_target_xid.  The value returned by those functions includes the
epoch in the computed result, which would cause strtoul() to fail where
unsigned long has a size of 32 bits once the epoch is incremented.

WAL records and 2PC data include only information about 32-bit XIDs and
it is not possible to have XIDs across more than one epoch, so
discarding the high bits from the transaction ID set has no impact on
recovery.  On the contrary, the use of strtoul() prevents a consistent
behavior across platforms depending on the size of unsigned long.

This commit changes the parsing of recovery_target_xid to use
pg_strtouint64() instead, available down to 9.6.  There is one TAP test
stressing recovery with recovery_target_xid, where a tweak based on
pg_reset{xlog,wal} is added to bump the XID epoch so as this change gets
tested, as per an idea from Alexander Lakhin.

Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/16780-107fd0c0385b1035@postgresql.org
Backpatch-through: 9.6

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 1683629ee38c1f7b3c53d8ba5f1707f2f04fd3a6..30b54312bf11c9d35be653dc98de65c659d8b403 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -11850,7 +11850,7 @@ check_recovery_target_xid(char **newval, void **extra, GucSource source)
                TransactionId *myextra;
 
                errno = 0;
-               xid = (TransactionId) strtoul(*newval, NULL, 0);
+               xid = (TransactionId) pg_strtouint64(*newval, NULL, 0);
                if (errno == EINVAL || errno == ERANGE)
                        return false;
 

diff --git a/src/test/recovery/t/003_recovery_targets.pl b/src/test/recovery/t/003_recovery_targets.pl
index 8d114eb7ad50d72079dc28ab4d1458f9d18a5249..47b41099182d6da592c092c1f48180fd8c6686e9 100644 (file)
--- a/src/test/recovery/t/003_recovery_targets.pl
+++ b/src/test/recovery/t/003_recovery_targets.pl
@@ -50,6 +50,10 @@ sub test_recovery_standby
 my $node_master = get_new_node('master');
 $node_master->init(has_archiving => 1, allows_streaming => 1);
 
+# Bump the transaction ID epoch.  This is useful to stress the portability
+# of recovery_target_xid parsing.
+system_or_bail('pg_resetwal', '--epoch', '1', $node_master->data_dir);
+
 # Start it
 $node_master->start;