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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
Download Patch File Download Diff File Expand all files Collapse all files

6
src/backend/access/transam/xlog.c
View File

@ -764,8 +764,7 @@ static ControlFileData *ControlFile = NULL;
* Convert values of GUCs measured in megabytes to equiv. segment count.
* Rounds down.
*/
#define ConvertToXSegs(x, segsize) \
((x) / ((segsize) / (1024 * 1024)))
#define ConvertToXSegs(x, segsize) XLogMBVarToSegs((x), (segsize))
/* The number of bytes in a WAL segment usable for WAL data. */
static int UsableBytesInSegment;
@ -9513,8 +9512,7 @@ GetWALAvailability(XLogRecPtr targetLSN)
XLogSegNo targetSeg; /* segid of targetLSN */
XLogSegNo oldestSeg; /* actual oldest segid */
XLogSegNo oldestSegMaxWalSize; /* oldest segid kept by max_wal_size */
XLogSegNo oldestSlotSeg = InvalidXLogRecPtr; /* oldest segid kept by
* slot */
XLogSegNo oldestSlotSeg; /* oldest segid kept by slot */
uint64 keepSegs;
/*

2
src/backend/catalog/system_views.sql
View File

@ -879,7 +879,7 @@ CREATE VIEW pg_replication_slots AS
L.restart_lsn,
L.confirmed_flush_lsn,
L.wal_status,
L.min_safe_lsn
L.safe_wal_size
FROM pg_get_replication_slots() AS L
LEFT JOIN pg_database D ON (L.datoid = D.oid);

44
src/backend/replication/slotfuncs.c
View File

@ -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);

7
src/include/access/xlog_internal.h
View File

@ -121,6 +121,13 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
#define XLByteToPrevSeg(xlrp, logSegNo, wal_segsz_bytes) \
logSegNo = ((xlrp) - 1) / (wal_segsz_bytes)
/*
* Convert values of GUCs measured in megabytes to equiv. segment count.
* Rounds down.
*/
#define XLogMBVarToSegs(mbvar, wal_segsz_bytes) \
((mbvar) / ((wal_segsz_bytes) / (1024 * 1024)))
/*
* Is an XLogRecPtr within a particular XLOG segment?
*

2
src/include/catalog/catversion.h
View File

@ -53,6 +53,6 @@
*/
/* yyyymmddN */
#define CATALOG_VERSION_NO 202007061
#define CATALOG_VERSION_NO 202007071
#endif

4
src/include/catalog/pg_proc.dat
View File

@ -10075,9 +10075,9 @@
proname => 'pg_get_replication_slots', prorows => '10', proisstrict => 'f',
proretset => 't', provolatile => 's', prorettype => 'record',
proargtypes => '',
proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,pg_lsn}',
proallargtypes => '{name,name,text,oid,bool,bool,int4,xid,xid,pg_lsn,pg_lsn,text,int8}',
proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o}',
proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,min_safe_lsn}',
proargnames => '{slot_name,plugin,slot_type,datoid,temporary,active,active_pid,xmin,catalog_xmin,restart_lsn,confirmed_flush_lsn,wal_status,safe_wal_size}',
prosrc => 'pg_get_replication_slots' },
{ oid => '3786', descr => 'set up a logical replication slot',
proname => 'pg_create_logical_replication_slot', provolatile => 'v',

22
src/test/recovery/t/019_replslot_limit.pl
View File

@ -28,7 +28,7 @@ $node_master->safe_psql('postgres',
# The slot state and remain should be null before the first connection
my $result = $node_master->safe_psql('postgres',
"SELECT restart_lsn IS NULL, wal_status is NULL, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT restart_lsn IS NULL, wal_status is NULL, safe_wal_size is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "t|t|t", 'check the state of non-reserved slot is "unknown"');
@ -52,9 +52,9 @@ $node_master->wait_for_catchup($node_standby, 'replay', $start_lsn);
# Stop standby
$node_standby->stop;
# Preparation done, the slot is the state "normal" now
# Preparation done, the slot is the state "reserved" now
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT wal_status, safe_wal_size IS NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "reserved|t", 'check the catching-up state');
@ -64,7 +64,7 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
# The slot is always "safe" when fitting max_wal_size
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT wal_status, safe_wal_size IS NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "reserved|t",
'check that it is safe if WAL fits in max_wal_size');
@ -74,7 +74,7 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
# The slot is always "safe" when max_slot_wal_keep_size is not set
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT wal_status, safe_wal_size IS NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "reserved|t", 'check that slot is working');
@ -94,9 +94,7 @@ max_slot_wal_keep_size = ${max_slot_wal_keep_size_mb}MB
));
$node_master->reload;
# The slot is in safe state. The distance from the min_safe_lsn should
# be as almost (max_slot_wal_keep_size - 1) times large as the segment
# size
# The slot is in safe state.
$result = $node_master->safe_psql('postgres',
"SELECT wal_status FROM pg_replication_slots WHERE slot_name = 'rep1'");
@ -110,7 +108,7 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
$result = $node_master->safe_psql('postgres',
"SELECT wal_status FROM pg_replication_slots WHERE slot_name = 'rep1'");
is($result, "reserved",
'check that min_safe_lsn gets close to the current LSN');
'check that safe_wal_size gets close to the current LSN');
# The standby can reconnect to master
$node_standby->start;
@ -152,9 +150,9 @@ $node_master->safe_psql('postgres', "CHECKPOINT;");
# Advance WAL again without checkpoint; remain goes to 0.
advance_wal($node_master, 1);
# Slot gets into 'unreserved' state
# Slot gets into 'unreserved' state and safe_wal_size is negative
$result = $node_master->safe_psql('postgres',
"SELECT wal_status, min_safe_lsn is NULL FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT wal_status, safe_wal_size <= 0 FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "unreserved|t",
'check that the slot state changes to "unreserved"');
@ -186,7 +184,7 @@ ok( find_in_log(
# This slot should be broken
$result = $node_master->safe_psql('postgres',
"SELECT slot_name, active, restart_lsn IS NULL, wal_status, min_safe_lsn FROM pg_replication_slots WHERE slot_name = 'rep1'"
"SELECT slot_name, active, restart_lsn IS NULL, wal_status, safe_wal_size FROM pg_replication_slots WHERE slot_name = 'rep1'"
);
is($result, "rep1|f|t|lost|",
'check that the slot became inactive and the state "lost" persists');

4
src/test/regress/expected/rules.out
View File

@ -1464,8 +1464,8 @@ pg_replication_slots| SELECT l.slot_name,
l.restart_lsn,
l.confirmed_flush_lsn,
l.wal_status,
l.min_safe_lsn
FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, min_safe_lsn)
l.safe_wal_size
FROM (pg_get_replication_slots() l(slot_name, plugin, slot_type, datoid, temporary, active, active_pid, xmin, catalog_xmin, restart_lsn, confirmed_flush_lsn, wal_status, safe_wal_size)
LEFT JOIN pg_database d ON ((l.datoid = d.oid)));
pg_roles| SELECT pg_authid.rolname,
pg_authid.rolsuper,