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Morph pg_replication_slots.min_safe_lsn to safe_wal_size

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The previous definition of the column was almost universally disliked,
so provide this updated definition which is more useful for monitoring
purposes: a large positive value is good, while zero or a negative value
means danger.  This should be operationally more convenient.

Backpatch to 13, where the new column to pg_replication_slots (and the
feature it represents) were added.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reported-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Discussion: https://postgr.es/m/9ddfbf8c-2f67-904d-44ed-cf8bc5916228@oss.nttdata.com
This commit is contained in:
Alvaro Herrera
2020-07-07 13:08:00 -04:00
parent 6a5c750f3f
commit a8aaa0c786
9 changed files with 62 additions and 36 deletions
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44
src/backend/replication/slotfuncs.c
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@@ -242,6 +242,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
Tuplestorestate *tupstore;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
XLogRecPtr currlsn;
int slotno;
/* check to see if caller supports us returning a tuplestore */
@@ -274,6 +275,8 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
MemoryContextSwitchTo(oldcontext);
currlsn = GetXLogWriteRecPtr();
LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
for (slotno = 0; slotno < max_replication_slots; slotno++)
{
@@ -282,7 +285,6 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
Datum values[PG_GET_REPLICATION_SLOTS_COLS];
bool nulls[PG_GET_REPLICATION_SLOTS_COLS];
WALAvailability walstate;
XLogSegNo last_removed_seg;
int i;
if (!slot->in_use)
@@ -380,6 +382,8 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
* we looked. If checkpointer signalled the process to
* termination, then it's definitely lost; but if a process is
* still alive, then "unreserved" seems more appropriate.
*
* If we do change it, save the state for safe_wal_size below.
*/
if (!XLogRecPtrIsInvalid(slot_contents.data.restart_lsn))
{
@@ -387,10 +391,12 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
SpinLockAcquire(&slot->mutex);
pid = slot->active_pid;
slot_contents.data.restart_lsn = slot->data.restart_lsn;
SpinLockRelease(&slot->mutex);
if (pid != 0)
{
values[i++] = CStringGetTextDatum("unreserved");
walstate = WALAVAIL_UNRESERVED;
break;
}
}
@@ -398,18 +404,32 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
break;
}
if (max_slot_wal_keep_size_mb >= 0 &&
(walstate == WALAVAIL_RESERVED || walstate == WALAVAIL_EXTENDED) &&
((last_removed_seg = XLogGetLastRemovedSegno()) != 0))
{
XLogRecPtr min_safe_lsn;
XLogSegNoOffsetToRecPtr(last_removed_seg + 1, 0,
wal_segment_size, min_safe_lsn);
values[i++] = Int64GetDatum(min_safe_lsn);
}
else
/*
* safe_wal_size is only computed for slots that have not been lost,
* and only if there's a configured maximum size.
*/
if (walstate == WALAVAIL_REMOVED || max_slot_wal_keep_size_mb < 0)
nulls[i++] = true;
else
{
XLogSegNo targetSeg;
XLogSegNo keepSegs;
XLogSegNo failSeg;
XLogRecPtr failLSN;
XLByteToSeg(slot_contents.data.restart_lsn, targetSeg, wal_segment_size);
/* determine how many segments slots can be kept by slots ... */
keepSegs = XLogMBVarToSegs(max_slot_wal_keep_size_mb, wal_segment_size);
/* ... and override by wal_keep_segments as needed */
keepSegs = Max(keepSegs, wal_keep_segments);
/* if currpos reaches failLSN, we lose our segment */
failSeg = targetSeg + keepSegs + 1;
XLogSegNoOffsetToRecPtr(failSeg, 0, wal_segment_size, failLSN);
values[i++] = Int64GetDatum(failLSN - currlsn);
}
Assert(i == PG_GET_REPLICATION_SLOTS_COLS);