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Fix dropping replication slot (#6359) 

DESCRIPTION: Fixes dropping replication slots

As detected by a flaky test, Citus sometimes fails to drop replication
slots, possibly due to a race condition, at the end of a shard split.
With this PR, we retry to drop them in case of an `OBJECT_IN_USE` error,
consistently for 20 seconds.

fixes: #6326
(cherry picked from commit bae4b47c2f)
revert-shard-rebalancer-changes
Ahmet Gedemenli 2022-09-21 16:29:56 +03:00
parent a8e7c2cb09
commit ecaa0cda6d
1 changed files with 55 additions and 8 deletions
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63
src/backend/distributed/replication/multi_logical_replication.c
View File

@ -66,6 +66,7 @@
#include "utils/syscache.h"
#define STR_ERRCODE_UNDEFINED_OBJECT "42704"
#define STR_ERRCODE_OBJECT_IN_USE "55006"
#define REPLICATION_SLOT_CATALOG_TABLE_NAME "pg_replication_slots"
@ -1281,18 +1282,64 @@ DropPublications(MultiConnection *sourceConnection, HTAB *publicationInfoHash)
/*
* DropReplicationSlot drops the replication slot with the given name
* if it exists.
* if it exists. It retries if the command fails with an OBJECT_IN_USE error.
*/
static void
DropReplicationSlot(MultiConnection *connection, char *replicationSlotName)
{
ExecuteCriticalRemoteCommand(
connection,
psprintf(
"select pg_drop_replication_slot(slot_name) from "
REPLICATION_SLOT_CATALOG_TABLE_NAME
" where slot_name = %s",
quote_literal_cstr(replicationSlotName)));
int maxSecondsToTryDropping = 20;
bool raiseInterrupts = true;
PGresult *result = NULL;
/* we'll retry in case of an OBJECT_IN_USE error */
while (maxSecondsToTryDropping >= 0)
{
int querySent = SendRemoteCommand(
connection,
psprintf(
"select pg_drop_replication_slot(slot_name) from "
REPLICATION_SLOT_CATALOG_TABLE_NAME
" where slot_name = %s",
quote_literal_cstr(replicationSlotName))
);
if (querySent == 0)
{
ReportConnectionError(connection, ERROR);
}
result = GetRemoteCommandResult(connection, raiseInterrupts);
if (IsResponseOK(result))
{
/* no error, we are good to go */
break;
}
char *errorcode = PQresultErrorField(result, PG_DIAG_SQLSTATE);
if (errorcode != NULL && strcmp(errorcode, STR_ERRCODE_OBJECT_IN_USE) == 0 &&
maxSecondsToTryDropping > 0)
{
/* retry dropping the replication slot after sleeping for one sec */
maxSecondsToTryDropping--;
pg_usleep(1000);
}
else
{
/*
* Report error if:
* - Error code is not 55006 (Object In Use)
* - Or, we have made enough number of retries (currently 20), but didn't work
*/
ReportResultError(connection, result, ERROR);
}
PQclear(result);
ForgetResults(connection);
}
PQclear(result);
ForgetResults(connection);
}