database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-27 12:41:57 +03:00
Code Activity

Flush logical slots to disk during a shutdown checkpoint if required.

Browse Source 
It's entirely possible for a logical slot to have a confirmed_flush LSN
higher than the last value saved on disk while not being marked as dirty.
Currently, it is not a major problem but a later patch adding support for
the upgrade of slots relies on that value being properly flushed to disk.

It can also help avoid processing the same transactions again in some
boundary cases after the clean shutdown and restart.  Say, we process
some transactions for which we didn't send anything downstream (the
changes got filtered) but the confirm_flush LSN is updated due to
keepalives.  As we don't flush the latest value of confirm_flush LSN, it
may lead to processing the same changes again without this patch.

The approach taken by this patch has been suggested by Ashutosh Bapat.

Author: Vignesh C, Julien Rouhaud, Kuroda Hayato
Reviewed-by: Amit Kapila, Dilip Kumar, Michael Paquier, Ashutosh Bapat, Peter Smith, Hou Zhijie
Discussion: http://postgr.es/m/CAA4eK1JzJagMmb_E8D4au=GYQkxox0AfNBm1FbP7sy7t4YWXPQ@mail.gmail.com
Discussion: http://postgr.es/m/TYAPR01MB58664C81887B3AF2EB6B16E3F5939@TYAPR01MB5866.jpnprd01.prod.outlook.com
This commit is contained in:
Amit Kapila
2023-09-14 08:56:13 +05:30
parent a2e0d5e5f6
commit e0b2eed047
5 changed files with 145 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

37
src/backend/replication/slot.c
View File

@ -321,6 +321,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
slot->candidate_xmin_lsn = InvalidXLogRecPtr;
slot->candidate_restart_valid = InvalidXLogRecPtr;
slot->candidate_restart_lsn = InvalidXLogRecPtr;
slot->last_saved_confirmed_flush = InvalidXLogRecPtr;
/*
* Create the slot on disk. We haven't actually marked the slot allocated
@ -1572,11 +1573,13 @@ restart:
/*
* Flush all replication slots to disk.
*
* This needn't actually be part of a checkpoint, but it's a convenient
* location.
* It is convenient to flush dirty replication slots at the time of checkpoint.
* Additionally, in case of a shutdown checkpoint, we also identify the slots
* for which the confirmed_flush LSN has been updated since the last time it
* was saved and flush them.
*/
void
CheckPointReplicationSlots(void)
CheckPointReplicationSlots(bool is_shutdown)
{
int i;
@ -1601,6 +1604,30 @@ CheckPointReplicationSlots(void)
/* save the slot to disk, locking is handled in SaveSlotToPath() */
sprintf(path, "pg_replslot/%s", NameStr(s->data.name));
/*
* Slot's data is not flushed each time the confirmed_flush LSN is
* updated as that could lead to frequent writes. However, we decide
* to force a flush of all logical slot's data at the time of shutdown
* if the confirmed_flush LSN is changed since we last flushed it to
* disk. This helps in avoiding an unnecessary retreat of the
* confirmed_flush LSN after restart.
*/
if (is_shutdown && SlotIsLogical(s))
{
SpinLockAcquire(&s->mutex);
Assert(s->data.confirmed_flush >= s->last_saved_confirmed_flush);
if (s->data.invalidated == RS_INVAL_NONE &&
s->data.confirmed_flush != s->last_saved_confirmed_flush)
{
s->just_dirtied = true;
s->dirty = true;
}
SpinLockRelease(&s->mutex);
}
SaveSlotToPath(s, path, LOG);
}
LWLockRelease(ReplicationSlotAllocationLock);
@ -1873,11 +1900,12 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
/*
* Successfully wrote, unset dirty bit, unless somebody dirtied again
* already.
* already and remember the confirmed_flush LSN value.
*/
SpinLockAcquire(&slot->mutex);
if (!slot->just_dirtied)
slot->dirty = false;
slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush;
SpinLockRelease(&slot->mutex);
LWLockRelease(&slot->io_in_progress_lock);
@ -2074,6 +2102,7 @@ RestoreSlotFromDisk(const char *name)
/* initialize in memory state */
slot->effective_xmin = cp.slotdata.xmin;
slot->effective_catalog_xmin = cp.slotdata.catalog_xmin;
slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush;
slot->candidate_catalog_xmin = InvalidTransactionId;
slot->candidate_xmin_lsn = InvalidXLogRecPtr;