Skip WAL for new relfilenodes, under wal_level=minimal.

Until now, only selected bulk operations (e.g. COPY) did this.  If a
given relfilenode received both a WAL-skipping COPY and a WAL-logged
operation (e.g. INSERT), recovery could lose tuples from the COPY.  See
src/backend/access/transam/README section "Skipping WAL for New
RelFileNode" for the new coding rules.  Maintainers of table access
methods should examine that section.

To maintain data durability, just before commit, we choose between an
fsync of the relfilenode and copying its contents to WAL.  A new GUC,
wal_skip_threshold, guides that choice.  If this change slows a workload
that creates small, permanent relfilenodes under wal_level=minimal, try
adjusting wal_skip_threshold.  Users setting a timeout on COMMIT may
need to adjust that timeout, and log_min_duration_statement analysis
will reflect time consumption moving to COMMIT from commands like COPY.

Internally, this requires a reliable determination of whether
RollbackAndReleaseCurrentSubTransaction() would unlink a relation's
current relfilenode.  Introduce rd_firstRelfilenodeSubid.  Amend the
specification of rd_createSubid such that the field is zero when a new
rel has an old rd_node.  Make relcache.c retain entries for certain
dropped relations until end of transaction.

Back-patch to 9.5 (all supported versions).  This introduces a new WAL
record type, XLOG_GIST_ASSIGN_LSN, without bumping XLOG_PAGE_MAGIC.  As
always, update standby systems before master systems.  This changes
sizeof(RelationData) and sizeof(IndexStmt), breaking binary
compatibility for affected extensions.  (The most recent commit to
affect the same class of extensions was
089e4d405d0f3b94c74a2c6a54357a84a681754b.)

Kyotaro Horiguchi, reviewed (in earlier, similar versions) by Robert
Haas.  Heikki Linnakangas and Michael Paquier implemented earlier
designs that materially clarified the problem.  Reviewed, in earlier
designs, by Andrew Dunstan, Andres Freund, Alvaro Herrera, Tom Lane,
Fujii Masao, and Simon Riggs.  Reported by Martijn van Oosterhout.

Discussion: https://postgr.es/m/20150702220524.GA9392@svana.org

1 files changed, 119 insertions, 6 deletions

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 7332e6b5903..beabc6ffa63 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -66,7 +66,7 @@
 #define BUF_WRITTEN				0x01
 #define BUF_REUSABLE			0x02
 
-#define DROP_RELS_BSEARCH_THRESHOLD		20
+#define RELS_BSEARCH_THRESHOLD		20
 
 typedef struct PrivateRefCountEntry
 {
@@ -105,6 +105,19 @@ typedef struct CkptTsStatus
 	int			index;
 } CkptTsStatus;
 
+/*
+ * Type for array used to sort SMgrRelations
+ *
+ * FlushRelationsAllBuffers shares the same comparator function with
+ * DropRelFileNodesAllBuffers. Pointer to this struct and RelFileNode must be
+ * compatible.
+ */
+typedef struct SMgrSortArray
+{
+	RelFileNode rnode;			/* This must be the first member */
+	SMgrRelation srel;
+} SMgrSortArray;
+
 /* GUC variables */
 bool		zero_damaged_pages = false;
 int			bgwriter_lru_maxpages = 100;
@@ -3020,7 +3033,7 @@ DropRelFileNodesAllBuffers(RelFileNodeBackend *rnodes, int nnodes)
 	 * an exactly determined value, as it depends on many factors (CPU and RAM
 	 * speeds, amount of shared buffers etc.).
 	 */
-	use_bsearch = n > DROP_RELS_BSEARCH_THRESHOLD;
+	use_bsearch = n > RELS_BSEARCH_THRESHOLD;
 
 	/* sort the list of rnodes if necessary */
 	if (use_bsearch)
@@ -3271,6 +3284,104 @@ FlushRelationBuffers(Relation rel)
 }
 
 /* ---------------------------------------------------------------------
+ *		FlushRelationsAllBuffers
+ *
+ *		This function flushes out of the buffer pool all the pages of all
+ *		forks of the specified smgr relations.  It's equivalent to calling
+ *		FlushRelationBuffers once per fork per relation.  The relations are
+ *		assumed not to use local buffers.
+ * --------------------------------------------------------------------
+ */
+void
+FlushRelationsAllBuffers(SMgrRelation *smgrs, int nrels)
+{
+	int			i;
+	SMgrSortArray *srels;
+	bool		use_bsearch;
+
+	if (nrels == 0)
+		return;
+
+	/* fill-in array for qsort */
+	srels = palloc(sizeof(SMgrSortArray) * nrels);
+
+	for (i = 0; i < nrels; i++)
+	{
+		Assert(!RelFileNodeBackendIsTemp(smgrs[i]->smgr_rnode));
+
+		srels[i].rnode = smgrs[i]->smgr_rnode.node;
+		srels[i].srel = smgrs[i];
+	}
+
+	/*
+	 * Save the bsearch overhead for low number of relations to sync. See
+	 * DropRelFileNodesAllBuffers for details.
+	 */
+	use_bsearch = nrels > RELS_BSEARCH_THRESHOLD;
+
+	/* sort the list of SMgrRelations if necessary */
+	if (use_bsearch)
+		pg_qsort(srels, nrels, sizeof(SMgrSortArray), rnode_comparator);
+
+	/* Make sure we can handle the pin inside the loop */
+	ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
+
+	for (i = 0; i < NBuffers; i++)
+	{
+		SMgrSortArray *srelent = NULL;
+		BufferDesc *bufHdr = GetBufferDescriptor(i);
+		uint32		buf_state;
+
+		/*
+		 * As in DropRelFileNodeBuffers, an unlocked precheck should be safe
+		 * and saves some cycles.
+		 */
+
+		if (!use_bsearch)
+		{
+			int			j;
+
+			for (j = 0; j < nrels; j++)
+			{
+				if (RelFileNodeEquals(bufHdr->tag.rnode, srels[j].rnode))
+				{
+					srelent = &srels[j];
+					break;
+				}
+			}
+
+		}
+		else
+		{
+			srelent = bsearch((const void *) &(bufHdr->tag.rnode),
+							  srels, nrels, sizeof(SMgrSortArray),
+							  rnode_comparator);
+		}
+
+		/* buffer doesn't belong to any of the given relfilenodes; skip it */
+		if (srelent == NULL)
+			continue;
+
+		ReservePrivateRefCountEntry();
+
+		buf_state = LockBufHdr(bufHdr);
+		if (RelFileNodeEquals(bufHdr->tag.rnode, srelent->rnode) &&
+			(buf_state & (BM_VALID | BM_DIRTY)) == (BM_VALID | BM_DIRTY))
+		{
+			PinBuffer_Locked(bufHdr);
+			LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_SHARED);
+			FlushBuffer(bufHdr, srelent->srel);
+			LWLockRelease(BufferDescriptorGetContentLock(bufHdr));
+			UnpinBuffer(bufHdr, true);
+		}
+		else
+			UnlockBufHdr(bufHdr, buf_state);
+	}
+
+	pfree(srels);
+}
+
+/* ---------------------------------------------------------------------
  *		FlushDatabaseBuffers
  *
  *		This function writes all dirty pages of a database out to disk
@@ -3471,13 +3582,15 @@ MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
 			(pg_atomic_read_u32(&bufHdr->state) & BM_PERMANENT))
 		{
 			/*
-			 * If we're in recovery we cannot dirty a page because of a hint.
-			 * We can set the hint, just not dirty the page as a result so the
-			 * hint is lost when we evict the page or shutdown.
+			 * If we must not write WAL, due to a relfilenode-specific
+			 * condition or being in recovery, don't dirty the page.  We can
+			 * set the hint, just not dirty the page as a result so the hint
+			 * is lost when we evict the page or shutdown.
 			 *
 			 * See src/backend/storage/page/README for longer discussion.
 			 */
-			if (RecoveryInProgress())
+			if (RecoveryInProgress() ||
+				RelFileNodeSkippingWAL(bufHdr->tag.rnode))
 				return;
 
 			/*