From eadcb7a2377a7a68dee24f750b61a2ac0d7f9f40 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Wed, 14 Mar 2018 11:53:56 -0300
Subject: [PATCH] Log when a BRIN autosummarization request fails
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Autovacuum's 'workitem' request queue is of limited size, so requests
can fail if they arrive more quickly than autovacuum can process them.
Emit a log message when this happens, to provide better visibility of
this.

Backpatch to 10.  While this represents an API change for
AutoVacuumRequestWork, that function is not yet prepared to deal with
external modules calling it, so there doesn't seem to be any risk (other
than log spam, that is.)

Author: Masahiko Sawada
Reviewed-by: Fabrízio Mello, Ildar Musin, Álvaro Herrera
Discussion: https://postgr.es/m/CAD21AoB1HrQhp6_4rTyHN5kWEJCEsG8YzsjZNt-ctoXSn5Uisw@mail.gmail.com
---
 doc/src/sgml/brin.sgml              | 12 ++++++++++++
 src/backend/access/brin/brin.c      | 16 +++++++++++++---
 src/backend/postmaster/autovacuum.c |  7 ++++++-
 src/include/postmaster/autovacuum.h |  2 +-
 4 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/doc/src/sgml/brin.sgml b/doc/src/sgml/brin.sgml
index 8dcc29925b..8aef786778 100644
--- a/doc/src/sgml/brin.sgml
+++ b/doc/src/sgml/brin.sgml
@@ -86,6 +86,18 @@
    representation because the existing values have changed.
   </para>
 
+  <para>
+   When autosummarization is enabled, each time a page range is filled a
+   request is sent to autovacuum for it to execute a targeted summarization
+   for that range, to be fulfilled at the end of the next worker run on the
+   same database.  If the request queue is full, the request is not recorded
+   and a message is sent to the server log:
+<screen>
+LOG:  request for BRIN range summarization for index "brin_wi_idx" page 128 was not recorded
+</screen>
+   When this happens, the range will be summarized normally during the next
+   regular vacuum of the table.
+  </para>
  </sect2>
 </sect1>
 
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 4f0ff79cb4..7f4600f18d 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -187,9 +187,19 @@ brininsert(Relation idxRel, Datum *values, bool *nulls,
 				brinGetTupleForHeapBlock(revmap, lastPageRange, &buf, &off,
 										 NULL, BUFFER_LOCK_SHARE, NULL);
 			if (!lastPageTuple)
-				AutoVacuumRequestWork(AVW_BRINSummarizeRange,
-									  RelationGetRelid(idxRel),
-									  lastPageRange);
+			{
+				bool	recorded;
+
+				recorded = AutoVacuumRequestWork(AVW_BRINSummarizeRange,
+												 RelationGetRelid(idxRel),
+												 lastPageRange);
+				if (!recorded)
+					ereport(LOG,
+							(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+							 errmsg("request for BRIN range summarization for index \"%s\" page %u was not recorded",
+									RelationGetRelationName(idxRel),
+									lastPageRange)));
+			}
 			else
 				LockBuffer(buf, BUFFER_LOCK_UNLOCK);
 		}
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index ec2de9d9a3..70e08b552a 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -3227,12 +3227,14 @@ AutoVacuumingActive(void)
 
 /*
  * Request one work item to the next autovacuum run processing our database.
+ * Return false if the request can't be recorded.
  */
-void
+bool
 AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
 					  BlockNumber blkno)
 {
 	int			i;
+	bool		result = false;
 
 	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
 
@@ -3252,12 +3254,15 @@ AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
 		workitem->avw_database = MyDatabaseId;
 		workitem->avw_relation = relationId;
 		workitem->avw_blockNumber = blkno;
+		result = true;
 
 		/* done */
 		break;
 	}
 
 	LWLockRelease(AutovacuumLock);
+
+	return result;
 }
 
 /*
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index 3469915ae2..816f031c01 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -71,7 +71,7 @@ extern void AutovacuumWorkerIAm(void);
 extern void AutovacuumLauncherIAm(void);
 #endif
 
-extern void AutoVacuumRequestWork(AutoVacuumWorkItemType type,
+extern bool AutoVacuumRequestWork(AutoVacuumWorkItemType type,
 					  Oid relationId, BlockNumber blkno);
 
 /* shared memory stuff */
-- 
2.40.0