3 files changed, 92 insertions, 0 deletions

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index b553518bab6..745b1f1d891 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1723,6 +1723,46 @@ ZeroMultiXactMemberPage(int pageno, bool writeXlog)
 }
 
 /*
+ * MaybeExtendOffsetSlru
+ *		Extend the offsets SLRU area, if necessary
+ *
+ * After a binary upgrade from <= 9.2, the pg_multixact/offset SLRU area might
+ * contain files that are shorter than necessary; this would occur if the old
+ * installation had used multixacts beyond the first page (files cannot be
+ * copied, because the on-disk representation is different).  pg_upgrade would
+ * update pg_control to set the next offset value to be at that position, so
+ * that tuples marked as locked by such MultiXacts would be seen as visible
+ * without having to consult multixact.  However, trying to create and use a
+ * new MultiXactId would result in an error because the page on which the new
+ * value would reside does not exist.  This routine is in charge of creating
+ * such pages.
+ */
+static void
+MaybeExtendOffsetSlru(void)
+{
+	int			pageno;
+
+	pageno = MultiXactIdToOffsetPage(MultiXactState->nextMXact);
+
+	LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
+
+	if (!SimpleLruDoesPhysicalPageExist(MultiXactOffsetCtl, pageno))
+	{
+		int		slotno;
+
+		/*
+		 * Fortunately for us, SimpleLruWritePage is already prepared to deal
+		 * with creating a new segment file even if the page we're writing is
+		 * not the first in it, so this is enough.
+		 */
+		slotno = ZeroMultiXactOffsetPage(pageno, false);
+		SimpleLruWritePage(MultiXactOffsetCtl, slotno);
+	}
+
+	LWLockRelease(MultiXactOffsetControlLock);
+}
+
+/*
  * This must be called ONCE during postmaster or standalone-backend startup.
  *
  * StartupXLOG has already established nextMXact/nextOffset by calling
@@ -1742,6 +1782,13 @@ StartupMultiXact(void)
 	int			entryno;
 	int			flagsoff;
 
+	/*
+	 * During a binary upgrade, make sure that the offsets SLRU is large
+	 * enough to contain the next value that would be created.
+	 */
+	if (IsBinaryUpgrade)
+		MaybeExtendOffsetSlru();
+
 	/* Clean up offsets state */
 	LWLockAcquire(MultiXactOffsetControlLock, LW_EXCLUSIVE);
 
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 5a8f654fb73..5e53593a8f2 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -563,6 +563,50 @@ SimpleLruWritePage(SlruCtl ctl, int slotno)
 	SlruInternalWritePage(ctl, slotno, NULL);
 }
 
+/*
+ * Return whether the given page exists on disk.
+ *
+ * A false return means that either the file does not exist, or that it's not
+ * large enough to contain the given page.
+ */
+bool
+SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno)
+{
+	int			segno = pageno / SLRU_PAGES_PER_SEGMENT;
+	int			rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
+	int			offset = rpageno * BLCKSZ;
+	char		path[MAXPGPATH];
+	int			fd;
+	bool		result;
+	off_t		endpos;
+
+	SlruFileName(ctl, path, segno);
+
+	fd = OpenTransientFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
+	if (fd < 0)
+	{
+		/* expected: file doesn't exist */
+		if (errno == ENOENT)
+			return false;
+
+		/* report error normally */
+		slru_errcause = SLRU_OPEN_FAILED;
+		slru_errno = errno;
+		SlruReportIOError(ctl, pageno, 0);
+	}
+
+	if ((endpos = lseek(fd, 0, SEEK_END)) < 0)
+	{
+		slru_errcause = SLRU_OPEN_FAILED;
+		slru_errno = errno;
+		SlruReportIOError(ctl, pageno, 0);
+	}
+
+	result = endpos >= (off_t) (offset + BLCKSZ);
+
+	CloseTransientFile(fd);
+	return result;
+}
 
 /*
  * Physical read of a (previously existing) page into a buffer slot
diff --git a/src/include/access/slru.h b/src/include/access/slru.h
index 29ae9e0e5c1..7e81e0f1135 100644
--- a/src/include/access/slru.h
+++ b/src/include/access/slru.h
@@ -145,6 +145,7 @@ extern int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno,
 extern void SimpleLruWritePage(SlruCtl ctl, int slotno);
 extern void SimpleLruFlush(SlruCtl ctl, bool checkpoint);
 extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage);
+extern bool SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno);
 
 typedef bool (*SlruScanCallback) (SlruCtl ctl, char *filename, int segpage,
 											  void *data);