From 14d2bb4941e6bdf181f274d81314415781933079 Mon Sep 17 00:00:00 2001
From: Noah Misch <noah@leadboat.com>
Date: Sat, 21 Mar 2020 09:38:33 -0700
Subject: Back-patch log_newpage_range().

Back-patch a subset of commit 9155580fd5fc2a0cbb23376dfca7cd21f59c2c7b
to v11, v10, 9.6, and 9.5.  Include the latest repairs to this function.
Use a new XLOG_FPI_MULTI value instead of reusing XLOG_FPI.  That way,
if an older server reads WAL from this function, that server will PANIC
instead of applying just one page of the record.  The next commit adds a
call to this function.

Discussion: https://postgr.es/m/20200304.162919.898938381201316571.horikyota.ntt@gmail.com
---
 src/backend/access/transam/xloginsert.c | 88 +++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

(limited to 'src/backend/access/transam/xloginsert.c')

diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
index d1419441334..50119b5bb7b 100644
--- a/src/backend/access/transam/xloginsert.c
+++ b/src/backend/access/transam/xloginsert.c
@@ -986,6 +986,94 @@ log_newpage_buffer(Buffer buffer, bool page_std)
 	return log_newpage(&rnode, forkNum, blkno, page, page_std);
 }
 
+/*
+ * WAL-log a range of blocks in a relation.
+ *
+ * An image of all pages with block numbers 'startblk' <= X < 'endblk' is
+ * written to the WAL. If the range is large, this is done in multiple WAL
+ * records.
+ *
+ * If all page follows the standard page layout, with a PageHeader and unused
+ * space between pd_lower and pd_upper, set 'page_std' to true. That allows
+ * the unused space to be left out from the WAL records, making them smaller.
+ *
+ * NOTE: This function acquires exclusive-locks on the pages. Typically, this
+ * is used on a newly-built relation, and the caller is holding a
+ * AccessExclusiveLock on it, so no other backend can be accessing it at the
+ * same time. If that's not the case, you must ensure that this does not
+ * cause a deadlock through some other means.
+ */
+void
+log_newpage_range(Relation rel, ForkNumber forkNum,
+				  BlockNumber startblk, BlockNumber endblk,
+				  bool page_std)
+{
+	int			flags;
+	BlockNumber blkno;
+
+	flags = REGBUF_FORCE_IMAGE;
+	if (page_std)
+		flags |= REGBUF_STANDARD;
+
+	/*
+	 * Iterate over all the pages in the range. They are collected into
+	 * batches of XLR_MAX_BLOCK_ID pages, and a single WAL-record is written
+	 * for each batch.
+	 */
+	XLogEnsureRecordSpace(XLR_MAX_BLOCK_ID - 1, 0);
+
+	blkno = startblk;
+	while (blkno < endblk)
+	{
+		Buffer		bufpack[XLR_MAX_BLOCK_ID];
+		XLogRecPtr	recptr;
+		int			nbufs;
+		int			i;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/* Collect a batch of blocks. */
+		nbufs = 0;
+		while (nbufs < XLR_MAX_BLOCK_ID && blkno < endblk)
+		{
+			Buffer		buf = ReadBufferExtended(rel, forkNum, blkno,
+												 RBM_NORMAL, NULL);
+
+			LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
+
+			/*
+			 * Completely empty pages are not WAL-logged. Writing a WAL record
+			 * would change the LSN, and we don't want that. We want the page
+			 * to stay empty.
+			 */
+			if (!PageIsNew(BufferGetPage(buf)))
+				bufpack[nbufs++] = buf;
+			else
+				UnlockReleaseBuffer(buf);
+			blkno++;
+		}
+
+		/* Write WAL record for this batch. */
+		XLogBeginInsert();
+
+		START_CRIT_SECTION();
+		for (i = 0; i < nbufs; i++)
+		{
+			XLogRegisterBuffer(i, bufpack[i], flags);
+			MarkBufferDirty(bufpack[i]);
+		}
+
+		recptr = XLogInsert(RM_XLOG_ID, XLOG_FPI_MULTI);
+
+		for (i = 0; i < nbufs; i++)
+		{
+			PageSetLSN(BufferGetPage(bufpack[i]), recptr);
+			UnlockReleaseBuffer(bufpack[i]);
+		}
+		END_CRIT_SECTION();
+	}
+}
+
 /*
  * Allocate working buffers needed for WAL record construction.
  */
-- 
cgit v1.2.3