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Rework redundant code in subtrans.c

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When this code was written the duplicity didn't matter, but with all the
SLRU-bank stuff we just added, it has become excessive.  Turn it into a
simpler loop with no code duplication.  Also add a test so that this
code becomes covered.

Discussion: https://postgr.es/m/202403041517.3a35jw53os65@alvherre.pgsql
This commit is contained in:
Alvaro Herrera 2024-03-05 12:09:18 +01:00
parent 030e10ff1a
commit 1a2654b32b
No known key found for this signature in database
GPG Key ID: 1C20ACB9D5C564AE
2 changed files with 49 additions and 22 deletions
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29
src/backend/access/transam/subtrans.c
View File

@ -311,7 +311,7 @@ StartupSUBTRANS(TransactionId oldestActiveXID)
FullTransactionId nextXid; FullTransactionId nextXid;
int64 startPage; int64 startPage;
int64 endPage; int64 endPage;
LWLock *prevlock; LWLock *prevlock = NULL;
LWLock *lock; LWLock *lock;
/* /*
@ -324,42 +324,27 @@ StartupSUBTRANS(TransactionId oldestActiveXID)
nextXid = TransamVariables->nextXid; nextXid = TransamVariables->nextXid;
endPage = TransactionIdToPage(XidFromFullTransactionId(nextXid)); endPage = TransactionIdToPage(XidFromFullTransactionId(nextXid));
prevlock = SimpleLruGetBankLock(SubTransCtl, startPage); for (;;)
LWLockAcquire(prevlock, LW_EXCLUSIVE);
while (startPage != endPage)
{ {
lock = SimpleLruGetBankLock(SubTransCtl, startPage); lock = SimpleLruGetBankLock(SubTransCtl, startPage);
/*
* Check if we need to acquire the lock on the new bank then release
* the lock on the old bank and acquire on the new bank.
*/
if (prevlock != lock) if (prevlock != lock)
{ {
LWLockRelease(prevlock); if (prevlock)
LWLockRelease(prevlock);
LWLockAcquire(lock, LW_EXCLUSIVE); LWLockAcquire(lock, LW_EXCLUSIVE);
prevlock = lock; prevlock = lock;
} }
(void) ZeroSUBTRANSPage(startPage); (void) ZeroSUBTRANSPage(startPage);
if (startPage == endPage)
break;
startPage++; startPage++;
/* must account for wraparound */ /* must account for wraparound */
if (startPage > TransactionIdToPage(MaxTransactionId)) if (startPage > TransactionIdToPage(MaxTransactionId))
startPage = 0; startPage = 0;
} }
lock = SimpleLruGetBankLock(SubTransCtl, startPage);
/*
* Check if we need to acquire the lock on the new bank then release the
* lock on the old bank and acquire on the new bank.
*/
if (prevlock != lock)
{
LWLockRelease(prevlock);
LWLockAcquire(lock, LW_EXCLUSIVE);
}
(void) ZeroSUBTRANSPage(startPage);
LWLockRelease(lock); LWLockRelease(lock);
} }

42
src/test/recovery/t/009_twophase.pl
View File

@ -45,6 +45,10 @@ $node_london->backup('london_backup');
my $node_paris = PostgreSQL::Test::Cluster->new('paris'); my $node_paris = PostgreSQL::Test::Cluster->new('paris');
$node_paris->init_from_backup($node_london, 'london_backup', $node_paris->init_from_backup($node_london, 'london_backup',
has_streaming => 1); has_streaming => 1);
$node_paris->append_conf(
'postgresql.conf', qq(
subtransaction_buffers = 32
));
$node_paris->start; $node_paris->start;
# Switch to synchronous replication in both directions # Switch to synchronous replication in both directions
@ -481,4 +485,42 @@ is( $psql_out,
qq{27|issued to paris}, qq{27|issued to paris},
"Check expected t_009_tbl2 data on standby"); "Check expected t_009_tbl2 data on standby");
# Exercise the 2PC recovery code in StartupSUBTRANS, which is concerned with
# ensuring that enough pg_subtrans pages exist on disk to cover the range of
# prepared transactions at server start time. There's not much we can verify
# directly, but let's at least get the code to run.
$cur_standby->stop();
configure_and_reload($cur_primary, "synchronous_standby_names = ''");
$cur_primary->safe_psql('postgres', "CHECKPOINT");
my $start_lsn =
$cur_primary->safe_psql('postgres', 'select pg_current_wal_insert_lsn()');
$cur_primary->safe_psql('postgres',
"CREATE TABLE test(); BEGIN; CREATE TABLE test1(); PREPARE TRANSACTION 'foo';"
);
my $osubtrans = $cur_primary->safe_psql('postgres',
"select 'pg_subtrans/'||f, s.size from pg_ls_dir('pg_subtrans') f, pg_stat_file('pg_subtrans/'||f) s"
);
$cur_primary->pgbench(
'--no-vacuum --client=5 --transactions=1000',
0,
[],
[],
'pgbench run to cause pg_subtrans traffic',
{
'009_twophase.pgb' => 'insert into test default values'
});
# StartupSUBTRANS is exercised with a wide range of visible XIDs in this
# stop/start sequence, because we left a prepared transaction open above.
# Also, setting subtransaction_buffers to 32 above causes to switch SLRU
# bank, for additional code coverage.
$cur_primary->stop;
$cur_primary->start;
my $nsubtrans = $cur_primary->safe_psql('postgres',
"select 'pg_subtrans/'||f, s.size from pg_ls_dir('pg_subtrans') f, pg_stat_file('pg_subtrans/'||f) s"
);
isnt($osubtrans, $nsubtrans, "contents of pg_subtrans/ have changed");
done_testing(); done_testing();