At Tue, 23 Jun 2020 19:06:25 -0400, Alvaro Herrera <alvhe...@2ndquadrant.com>
wrote in
> On 2020-Jun-16, Kyotaro Horiguchi wrote:
>
> > I saw that the "reserved" is the state where slots are working to
> > retain segments, and "normal" is the state to indicate that "WAL
> > segments are within max_wal_size", which is orthogonal to the notion
> > of "reserved". So it seems to me useless when the retained WAL
> > segments cannot exceeds max_wal_size.
> >
> > With longer description they would be:
> >
> > "reserved under max_wal_size"
> > "reserved over max_wal_size"
> > "lost some segements"
>
> > Come to think of that, I realized that my trouble was just the
> > wording. Are the following wordings make sense to you?
> >
> > "reserved" - retained within max_wal_size
> > "extended" - retained over max_wal_size
> > "lost" - lost some segments
>
> So let's add Unreserved to denote the state that it's over the slot size
> but no segments have been removed yet:
Oh! Thanks for the more proper word. It looks good to me.
> * Reserved under max_wal_size
> * Extended past max_wal_size, but still within wal_keep_segments or
> maximum slot size.
> * Unreserved Past wal_keep_segments and the maximum slot size, but
> not yet removed. Recoverable condition.
> * Lost lost segments. Unrecoverable condition.
Look good, too.
> It seems better to me to save the invalidation LSN in the persistent
> data rather than the in-memory data that's lost on restart. As is, we
> would lose the status in a restart, which doesn't seem good to me. It's
> just eight extra bytes to write ... should be pretty much free.
Agreed.
> This version I propose is based on the one you posted earlier today and
> is what I propose for commit.
- /* slot does not reserve WAL. Either deactivated, or has never been
active */
+ /*
+ * slot does not reserve WAL. Either deactivated, or has never been
active
+ */
Sorry, this is my fault. The change is useless. The code for
WALAVAIL_REMOVED looks good.
# Advance WAL again without checkpoint, reducing remain by 6 MB.
+$result = $node_master->safe_psql('postgres',
+ "SELECT wal_status, restart_lsn, min_safe_lsn FROM pg_replication_slots
WHERE slot_name = 'rep1'"
+);
+print $result, "\n";
Sorry this is my fault, too. Removed in the attached.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 5a66115df1..49a881b262 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -11239,19 +11239,29 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
Possible values are:
<itemizedlist>
<listitem>
- <para><literal>normal</literal> means that the claimed files
+ <para><literal>reserved</literal> means that the claimed files
are within <varname>max_wal_size</varname>.</para>
</listitem>
<listitem>
- <para><literal>reserved</literal> means
+ <para><literal>extended</literal> means
that <varname>max_wal_size</varname> is exceeded but the files are
- still held, either by some replication slot or
- by <varname>wal_keep_segments</varname>.</para>
+ still retained, either by the replication slot or
+ by <varname>wal_keep_segments</varname>.
+ </para>
</listitem>
<listitem>
- <para><literal>lost</literal> means that some WAL files are
- definitely lost and this slot cannot be used to resume replication
- anymore.</para>
+ <para>
+ <literal>unreserved</literal> means that the slot no longer
+ retains the required WAL files and some of them are to be removed at
+ the next checkpoint. This state can return
+ to <literal>reserved</literal> or <literal>extended</literal>.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <literal>lost</literal> means that some required WAL files have
+ been removed and this slot is no longer usable.
+ </para>
</listitem>
</itemizedlist>
The last two states are seen only when
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index a1256a103b..4a4bb30418 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9485,15 +9485,20 @@ CreateRestartPoint(int flags)
* (typically a slot's restart_lsn)
*
* Returns one of the following enum values:
- * * WALAVAIL_NORMAL means targetLSN is available because it is in the range
- * of max_wal_size.
*
- * * WALAVAIL_PRESERVED means it is still available by preserving extra
+ * * WALAVAIL_RESERVED means targetLSN is available and it is in the range of
+ * max_wal_size.
+ *
+ * * WALAVAIL_EXTENDED means it is still available by preserving extra
* segments beyond max_wal_size. If max_slot_wal_keep_size is smaller
* than max_wal_size, this state is not returned.
*
- * * WALAVAIL_REMOVED means it is definitely lost. A replication stream on
- * a slot with this LSN cannot continue.
+ * * WALAVAIL_UNRESERVED means it is being lost and the next checkpoint will
+ * remove reserved segments. The walsender using this slot may return to the
+ * above.
+ *
+ * * WALAVAIL_REMOVED means it has been removed. A replication stream on
+ * a slot with this LSN cannot continue after a restart.
*
* * WALAVAIL_INVALID_LSN means the slot hasn't been set to reserve WAL.
*/
@@ -9509,13 +9514,18 @@ GetWALAvailability(XLogRecPtr targetLSN)
* slot */
uint64 keepSegs;
- /* slot does not reserve WAL. Either deactivated, or has never been active */
+ /*
+ * slot does not reserve WAL. Either deactivated, or has never been active
+ */
if (XLogRecPtrIsInvalid(targetLSN))
return WALAVAIL_INVALID_LSN;
currpos = GetXLogWriteRecPtr();
- /* calculate oldest segment currently needed by slots */
+ /*
+ * calculate the oldest segment currently reserved by all slots,
+ * considering wal_keep_segments and max_slot_wal_keep_size
+ */
XLByteToSeg(targetLSN, targetSeg, wal_segment_size);
KeepLogSeg(currpos, &oldestSlotSeg);
@@ -9526,10 +9536,9 @@ GetWALAvailability(XLogRecPtr targetLSN)
*/
oldestSeg = XLogGetLastRemovedSegno() + 1;
- /* calculate oldest segment by max_wal_size and wal_keep_segments */
+ /* calculate oldest segment by max_wal_size */
XLByteToSeg(currpos, currSeg, wal_segment_size);
- keepSegs = ConvertToXSegs(Max(max_wal_size_mb, wal_keep_segments),
- wal_segment_size) + 1;
+ keepSegs = ConvertToXSegs(max_wal_size_mb, wal_segment_size) + 1;
if (currSeg > keepSegs)
oldestSegMaxWalSize = currSeg - keepSegs;
@@ -9537,27 +9546,23 @@ GetWALAvailability(XLogRecPtr targetLSN)
oldestSegMaxWalSize = 1;
/*
- * If max_slot_wal_keep_size has changed after the last call, the segment
- * that would been kept by the current setting might have been lost by the
- * previous setting. No point in showing normal or keeping status values
- * if the targetSeg is known to be lost.
+ * No point in returning reserved or extended status values if the
+ * targetSeg is known to be lost.
*/
- if (targetSeg >= oldestSeg)
+ if (targetSeg >= oldestSlotSeg)
{
- /*
- * show "normal" when targetSeg is within max_wal_size, even if
- * max_slot_wal_keep_size is smaller than max_wal_size.
- */
- if ((max_slot_wal_keep_size_mb <= 0 ||
- max_slot_wal_keep_size_mb >= max_wal_size_mb) &&
- oldestSegMaxWalSize <= targetSeg)
- return WALAVAIL_NORMAL;
-
- /* being retained by slots */
- if (oldestSlotSeg <= targetSeg)
+ /* show "reserved" when targetSeg is within max_wal_size */
+ if (targetSeg >= oldestSegMaxWalSize)
return WALAVAIL_RESERVED;
+
+ /* being retained by slots exceeding max_wal_size */
+ return WALAVAIL_EXTENDED;
}
+ /* WAL segments are no longer retained but haven't been removed yet */
+ if (targetSeg >= oldestSeg)
+ return WALAVAIL_UNRESERVED;
+
/* Definitely lost */
return WALAVAIL_REMOVED;
}
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a7bbcf3499..e8761f3a18 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1226,6 +1226,7 @@ restart:
(uint32) restart_lsn)));
SpinLockAcquire(&s->mutex);
+ s->data.invalidated_at = s->data.restart_lsn;
s->data.restart_lsn = InvalidXLogRecPtr;
SpinLockRelease(&s->mutex);
ReplicationSlotRelease();
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 06e4955de7..df854bc6e3 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -283,6 +283,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
bool nulls[PG_GET_REPLICATION_SLOTS_COLS];
WALAvailability walstate;
XLogSegNo last_removed_seg;
+ XLogRecPtr targetLSN;
int i;
if (!slot->in_use)
@@ -342,7 +343,15 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
else
nulls[i++] = true;
- walstate = GetWALAvailability(slot_contents.data.restart_lsn);
+ /*
+ * Report availability from invalidated_at when the slot has been
+ * invalidated; otherwise slots would appear as invalid without any
+ * more clues as to what happened.
+ */
+ targetLSN = XLogRecPtrIsInvalid(slot_contents.data.restart_lsn) ?
+ slot_contents.data.invalidated_at :
+ slot_contents.data.restart_lsn;
+ walstate = GetWALAvailability(targetLSN);
switch (walstate)
{
@@ -350,24 +359,47 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
nulls[i++] = true;
break;
- case WALAVAIL_NORMAL:
- values[i++] = CStringGetTextDatum("normal");
- break;
-
case WALAVAIL_RESERVED:
values[i++] = CStringGetTextDatum("reserved");
break;
+ case WALAVAIL_EXTENDED:
+ values[i++] = CStringGetTextDatum("extended");
+ break;
+
+ case WALAVAIL_UNRESERVED:
+ values[i++] = CStringGetTextDatum("unreserved");
+ break;
+
case WALAVAIL_REMOVED:
+
+ /*
+ * If we read the restart_lsn long enough ago, maybe that file
+ * has been removed by now. However, the walsender could have
+ * moved forward enough that it jumped to another file after
+ * 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 (!XLogRecPtrIsInvalid(slot_contents.data.restart_lsn))
+ {
+ int pid;
+
+ SpinLockAcquire(&slot->mutex);
+ pid = slot->active_pid;
+ SpinLockRelease(&slot->mutex);
+ if (pid != 0)
+ {
+ values[i++] = CStringGetTextDatum("unreserved");
+ break;
+ }
+ }
values[i++] = CStringGetTextDatum("lost");
break;
-
- default:
- elog(ERROR, "invalid walstate: %d", (int) walstate);
}
if (max_slot_wal_keep_size_mb >= 0 &&
- (walstate == WALAVAIL_NORMAL || walstate == WALAVAIL_RESERVED) &&
+ (walstate == WALAVAIL_RESERVED || walstate == WALAVAIL_EXTENDED) &&
((last_removed_seg = XLogGetLastRemovedSegno()) != 0))
{
XLogRecPtr min_safe_lsn;
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 347a38f57c..77ac4e785f 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -270,8 +270,10 @@ extern CheckpointStatsData CheckpointStats;
typedef enum WALAvailability
{
WALAVAIL_INVALID_LSN, /* parameter error */
- WALAVAIL_NORMAL, /* WAL segment is within max_wal_size */
- WALAVAIL_RESERVED, /* WAL segment is reserved by a slot */
+ WALAVAIL_RESERVED, /* WAL segment is within max_wal_size */
+ WALAVAIL_EXTENDED, /* WAL segment is reserved by a slot or
+ * wal_keep_segments */
+ WALAVAIL_UNRESERVED, /* no longer reserved, but not removed yet */
WALAVAIL_REMOVED /* WAL segment has been removed */
} WALAvailability;
@@ -326,7 +328,7 @@ extern void ShutdownXLOG(int code, Datum arg);
extern void InitXLOGAccess(void);
extern void CreateCheckPoint(int flags);
extern bool CreateRestartPoint(int flags);
-extern WALAvailability GetWALAvailability(XLogRecPtr restart_lsn);
+extern WALAvailability GetWALAvailability(XLogRecPtr targetLSN);
extern XLogRecPtr CalculateMaxmumSafeLSN(void);
extern void XLogPutNextOid(Oid nextOid);
extern XLogRecPtr XLogRestorePoint(const char *rpName);
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 917876010e..31362585ec 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -79,6 +79,9 @@ typedef struct ReplicationSlotPersistentData
/* oldest LSN that might be required by this replication slot */
XLogRecPtr restart_lsn;
+ /* restart_lsn is copied here when the slot is invalidated */
+ XLogRecPtr invalidated_at;
+
/*
* Oldest LSN that the client has acked receipt for. This is used as the
* start_lsn point in case the client doesn't specify one, and also as a
diff --git a/src/test/recovery/t/019_replslot_limit.pl b/src/test/recovery/t/019_replslot_limit.pl
index cba7df920c..7d22ae5720 100644
--- a/src/test/recovery/t/019_replslot_limit.pl
+++ b/src/test/recovery/t/019_replslot_limit.pl
@@ -56,7 +56,7 @@ $node_standby->stop;
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "normal|t", 'check the catching-up state');
+is($result, "reserved|t", 'check the catching-up state');
# Advance WAL by five segments (= 5MB) on master
advance_wal($node_master, 1);
@@ -66,7 +66,8 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "normal|t", 'check that it is safe if WAL fits in max_wal_size');
+is($result, "reserved|t",
+ 'check that it is safe if WAL fits in max_wal_size');
advance_wal($node_master, 4);
$node_master->safe_psql('postgres', "CHECKPOINT;");
@@ -75,7 +76,7 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "normal|t", 'check that slot is working');
+is($result, "reserved|t", 'check that slot is working');
# The standby can reconnect to master
$node_standby->start;
@@ -99,7 +100,7 @@ $node_master->reload;
$result = $node_master->safe_psql('postgres',
"SELECT wal_status FROM pg_replication_slots WHERE slot_name = 'rep1'");
-is($result, "normal", 'check that max_slot_wal_keep_size is working');
+is($result, "reserved", 'check that max_slot_wal_keep_size is working');
# Advance WAL again then checkpoint, reducing remain by 2 MB.
advance_wal($node_master, 2);
@@ -108,7 +109,7 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
# The slot is still working
$result = $node_master->safe_psql('postgres',
"SELECT wal_status FROM pg_replication_slots WHERE slot_name = 'rep1'");
-is($result, "normal",
+is($result, "reserved",
'check that min_safe_lsn gets close to the current LSN');
# The standby can reconnect to master
@@ -125,7 +126,7 @@ advance_wal($node_master, 6);
$result = $node_master->safe_psql('postgres',
"SELECT wal_status as remain FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "normal",
+is($result, "extended",
'check that wal_keep_segments overrides max_slot_wal_keep_size');
# restore wal_keep_segments
$result = $node_master->safe_psql('postgres',
@@ -143,7 +144,7 @@ advance_wal($node_master, 6);
# Slot gets into 'reserved' state
$result = $node_master->safe_psql('postgres',
"SELECT wal_status FROM pg_replication_slots WHERE slot_name = 'rep1'");
-is($result, "reserved", 'check that the slot state changes to "reserved"');
+is($result, "extended", 'check that the slot state changes to "extended"');
# do checkpoint so that the next checkpoint runs too early
$node_master->safe_psql('postgres', "CHECKPOINT;");
@@ -151,11 +152,12 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
# Advance WAL again without checkpoint; remain goes to 0.
advance_wal($node_master, 1);
-# Slot gets into 'lost' state
+# Slot gets into 'unreserved' state
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "lost|t", 'check that the slot state changes to "lost"');
+is($result, "unreserved|t",
+ 'check that the slot state changes to "unreserved"');
# The standby still can connect to master before a checkpoint
$node_standby->start;
@@ -186,7 +188,8 @@ ok( find_in_log(
$result = $node_master->safe_psql('postgres',
"SELECT slot_name, active, restart_lsn IS NULL, wal_status, min_safe_lsn FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
-is($result, "rep1|f|t||", 'check that the slot became inactive');
+is($result, "rep1|f|t|lost|",
+ 'check that the slot became inactive and the state "lost" persists');
# The standby no longer can connect to the master
$logstart = get_log_size($node_standby);
