Fix WAL format incompatibility introduced by backpatching of 52ac6cd2d0

52ac6cd2d0 added new field to ginxlogDeletePage and was backpatched to 9.4.
That led to problems when patched postgres instance applies WAL records
generated by non-patched one.  WAL records generated by non-patched instance
don't contain new field, which patched one is expecting to see.

Thankfully, we can distinguish patched and non-patched WAL records by their data
size.  If we see that WAL record is generated by non-patched instance, we skip
processing of new field.  This commit comes with some assertions.  In
particular, if it appears that on some platform struct data size didn't change
then static assertion will trigger.

Reported-by: Simon Riggs
Discussion: https://postgr.es/m/CANP8%2Bj%2BK4whxf7ET7%2BgO%2BG-baC3-WxqqH%3DnV4X2CgfEPA3Yu3g%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Simon Riggs, Alvaro Herrera
Backpatch-through: 9.4

diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c
index b84ecf2ab1580c243aa7e216b55b37e0f7f9b26f..f3c82ac836cdbcaf6d53376041c8783f4fe15979 100644 (file)
--- a/src/backend/access/gin/ginxlog.c
+++ b/src/backend/access/gin/ginxlog.c
@@ -531,7 +531,24 @@ ginRedoDeletePage(XLogReaderState *record)
        page = BufferGetPage(dbuffer);
        Assert(GinPageIsData(page));
        GinPageGetOpaque(page)->flags = GIN_DELETED;
-       GinPageSetDeleteXid(page, data->deleteXid);
+
+       /*
+        * deleteXid field of ginxlogDeletePage was added during backpatching.
+        * But, non-backpatched instances will continue generate WAL without
+        * this field.  We should be able to correctly apply that.  We can
+        * distinguish new WAL records by size their data, because
+        * ginxlogDeletePage changes its size on both 32-bit and 64-bit
+        * platforms.
+        */
+       StaticAssertStmt(sizeof(ginxlogDeletePage) !=
+                        sizeof(ginxlogDeletePageOld),
+                        "ginxlogDeletePage size should be changed "
+                        "with addition of deleteXid field");
+       Assert(XLogRecGetDataLen(record) == sizeof(ginxlogDeletePage) ||
+              XLogRecGetDataLen(record) == sizeof(ginxlogDeletePageOld));
+       if (XLogRecGetDataLen(record) == sizeof(ginxlogDeletePage))
+           GinPageSetDeleteXid(page, data->deleteXid);
+
        PageSetLSN(page, lsn);
        MarkBufferDirty(dbuffer);
    }

diff --git a/src/include/access/ginxlog.h b/src/include/access/ginxlog.h
index b2f3126aa8a6e8fe7ed40d75201071038158f6ae..87b1e7bbda3239c38a0ab956aae538facf8ffe91 100644 (file)
--- a/src/include/access/ginxlog.h
+++ b/src/include/access/ginxlog.h
@@ -161,6 +161,16 @@ typedef struct ginxlogDeletePage
    TransactionId deleteXid;    /* last Xid which could see this page in scan */
 } ginxlogDeletePage;
 
+/*
+ * Previous version of ginxlogDeletePage struct, which didn't have deleteXid
+ * field.  Used for size comparison (see ginRedoDeletePage()).
+ */
+typedef struct ginxlogDeletePageOld
+{
+   OffsetNumber parentOffset;
+   BlockNumber rightLink;
+} ginxlogDeletePageOld;
+
 #define XLOG_GIN_UPDATE_META_PAGE 0x60
 
 /*