0001-Set-pd_lower-correctly-in-the-GIN-metapage.patch

From 607b4ab062652e7ffc0f95338c9265b09be18b56 Mon Sep 17 00:00:00 2001
From: amit <amitlangote09@gmail.com>
Date: Fri, 23 Jun 2017 11:20:41 +0900
Subject: [PATCH 1/3] Set pd_lower correctly in the GIN metapage.

Also tell xlog.c to treat the metapage like a standard page, so any
hole in it is compressed.
---
 src/backend/access/gin/ginfast.c   | 22 ++++++++++++++++++++--
 src/backend/access/gin/gininsert.c |  4 ++--
 src/backend/access/gin/ginutil.c   | 19 ++++++++++++++++++-
 src/backend/access/gin/ginxlog.c   | 24 +++++++++---------------
 4 files changed, 49 insertions(+), 20 deletions(-)

diff --git a/src/backend/access/gin/ginfast.c b/src/backend/access/gin/ginfast.c
index 59e435465a..d96529cf72 100644
--- a/src/backend/access/gin/ginfast.c
+++ b/src/backend/access/gin/ginfast.c
@@ -399,6 +399,15 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
 	/*
 	 * Write metabuffer, make xlog entry
 	 */
+
+	/*
+	 * Set pd_lower just past the end of the metadata.  This is not essential
+	 * but it makes the page look compressible to xlog.c, because we pass the
+	 * buffer containing this page to XLogRegisterBuffer() as a page with
+	 * standard layout.
+	 */
+	((PageHeader) metapage)->pd_lower =
+			((char *) metadata + sizeof(GinMetaPageData)) - (char *) metapage;
 	MarkBufferDirty(metabuffer);
 
 	if (needWal)
@@ -407,7 +416,7 @@ ginHeapTupleFastInsert(GinState *ginstate, GinTupleCollector *collector)
 
 		memcpy(&data.metadata, metadata, sizeof(GinMetaPageData));
 
-		XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT);
+		XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT | REGBUF_STANDARD);
 		XLogRegisterData((char *) &data, sizeof(ginxlogUpdateMeta));
 
 		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_UPDATE_META_PAGE);
@@ -572,6 +581,14 @@ shiftList(Relation index, Buffer metabuffer, BlockNumber newHead,
 			metadata->nPendingHeapTuples = 0;
 		}
 
+		/*
+		 * Set pd_lower just past the end of the metadata.  This is not
+		 * essential but it makes the page look compressible to xlog.c,
+		 * because we pass the buffer containing this page to
+		 * XLogRegisterBuffer() as page with standard layout.
+		 */
+		((PageHeader) metapage)->pd_lower =
+			((char *) metadata + sizeof(GinMetaPageData)) - (char *) metapage;
 		MarkBufferDirty(metabuffer);
 
 		for (i = 0; i < data.ndeleted; i++)
@@ -586,7 +603,8 @@ shiftList(Relation index, Buffer metabuffer, BlockNumber newHead,
 			XLogRecPtr	recptr;
 
 			XLogBeginInsert();
-			XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT);
+			XLogRegisterBuffer(0, metabuffer,
+							   REGBUF_WILL_INIT | REGBUF_STANDARD);
 			for (i = 0; i < data.ndeleted; i++)
 				XLogRegisterBuffer(i + 1, buffers[i], REGBUF_WILL_INIT);
 
diff --git a/src/backend/access/gin/gininsert.c b/src/backend/access/gin/gininsert.c
index 5378011f50..c9aa4ee147 100644
--- a/src/backend/access/gin/gininsert.c
+++ b/src/backend/access/gin/gininsert.c
@@ -348,7 +348,7 @@ ginbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 		Page		page;
 
 		XLogBeginInsert();
-		XLogRegisterBuffer(0, MetaBuffer, REGBUF_WILL_INIT);
+		XLogRegisterBuffer(0, MetaBuffer, REGBUF_WILL_INIT | REGBUF_STANDARD);
 		XLogRegisterBuffer(1, RootBuffer, REGBUF_WILL_INIT);
 
 		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_CREATE_INDEX);
@@ -447,7 +447,7 @@ ginbuildempty(Relation index)
 	START_CRIT_SECTION();
 	GinInitMetabuffer(MetaBuffer);
 	MarkBufferDirty(MetaBuffer);
-	log_newpage_buffer(MetaBuffer, false);
+	log_newpage_buffer(MetaBuffer, true);
 	GinInitBuffer(RootBuffer, GIN_LEAF);
 	MarkBufferDirty(RootBuffer);
 	log_newpage_buffer(RootBuffer, false);
diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c
index 136ea27718..d680849e9d 100644
--- a/src/backend/access/gin/ginutil.c
+++ b/src/backend/access/gin/ginutil.c
@@ -374,6 +374,15 @@ GinInitMetabuffer(Buffer b)
 	metadata->nDataPages = 0;
 	metadata->nEntries = 0;
 	metadata->ginVersion = GIN_CURRENT_VERSION;
+
+	/*
+	 * Set pd_lower just past the end of the metadata.  This is not essential
+	 * but it makes the page look compressible to xlog.c, because we pass the
+	 * buffer containing this page to XLogRegisterBuffer() as a page with
+	 * standard layout.
+	 */
+	((PageHeader) page)->pd_lower =
+			((char *) metadata + sizeof(GinMetaPageData)) - (char *) page;
 }
 
 /*
@@ -676,6 +685,14 @@ ginUpdateStats(Relation index, const GinStatsData *stats)
 	metadata->nDataPages = stats->nDataPages;
 	metadata->nEntries = stats->nEntries;
 
+	/*
+	 * Set pd_lower just past the end of the metadata.  This is not essential
+	 * but it makes the page look compressible to xlog.c, because we pass the
+	 * buffer containing this page to XLogRegisterBuffer() as page with
+	 * standard layout.
+	 */
+	((PageHeader) metapage)->pd_lower =
+		((char *) metadata + sizeof(GinMetaPageData)) - (char *) metapage;
 	MarkBufferDirty(metabuffer);
 
 	if (RelationNeedsWAL(index))
@@ -690,7 +707,7 @@ ginUpdateStats(Relation index, const GinStatsData *stats)
 
 		XLogBeginInsert();
 		XLogRegisterData((char *) &data, sizeof(ginxlogUpdateMeta));
-		XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT);
+		XLogRegisterBuffer(0, metabuffer, REGBUF_WILL_INIT | REGBUF_STANDARD);
 
 		recptr = XLogInsert(RM_GIN_ID, XLOG_GIN_UPDATE_META_PAGE);
 		PageSetLSN(metapage, recptr);
diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c
index 7ba04e324f..f5c11b2d9a 100644
--- a/src/backend/access/gin/ginxlog.c
+++ b/src/backend/access/gin/ginxlog.c
@@ -514,7 +514,7 @@ ginRedoUpdateMetapage(XLogReaderState *record)
 	Assert(BufferGetBlockNumber(metabuffer) == GIN_METAPAGE_BLKNO);
 	metapage = BufferGetPage(metabuffer);
 
-	GinInitPage(metapage, GIN_META, BufferGetPageSize(metabuffer));
+	GinInitMetabuffer(metabuffer);
 	memcpy(GinPageGetMeta(metapage), &data->metadata, sizeof(GinMetaPageData));
 	PageSetLSN(metapage, lsn);
 	MarkBufferDirty(metabuffer);
@@ -656,7 +656,7 @@ ginRedoDeleteListPages(XLogReaderState *record)
 	Assert(BufferGetBlockNumber(metabuffer) == GIN_METAPAGE_BLKNO);
 	metapage = BufferGetPage(metabuffer);
 
-	GinInitPage(metapage, GIN_META, BufferGetPageSize(metabuffer));
+	GinInitMetabuffer(metabuffer);
 
 	memcpy(GinPageGetMeta(metapage), &data->metadata, sizeof(GinMetaPageData));
 	PageSetLSN(metapage, lsn);
@@ -768,6 +768,7 @@ void
 gin_mask(char *pagedata, BlockNumber blkno)
 {
 	Page		page = (Page) pagedata;
+	PageHeader	pagehdr = (PageHeader) page;
 	GinPageOpaque opaque;
 
 	mask_page_lsn(page);
@@ -776,18 +777,11 @@ gin_mask(char *pagedata, BlockNumber blkno)
 	mask_page_hint_bits(page);
 
 	/*
-	 * GIN metapage doesn't use pd_lower/pd_upper. Other page types do. Hence,
-	 * we need to apply masking for those pages.
+	 * For GIN_DELETED page, the page is initialized to empty. Hence, mask
+	 * the page content.
 	 */
-	if (opaque->flags != GIN_META)
-	{
-		/*
-		 * For GIN_DELETED page, the page is initialized to empty. Hence, mask
-		 * the page content.
-		 */
-		if (opaque->flags & GIN_DELETED)
-			mask_page_content(page);
-		else
-			mask_unused_space(page);
-	}
+	if (opaque->flags & GIN_DELETED)
+		mask_page_content(page);
+	else if (pagehdr->pd_lower != 0)
+		mask_unused_space(page);
 }
-- 
2.11.0