Make XLOG_FPI_FOR_HINT records honor full_page_writes setting.

Commit 2c03216d83 changed XLOG_FPI_FOR_HINT records so that they always
included full-page images even when full_page_writes was disabled. However,
in this setting, they don't need to do that because hint bit updates don't
need to be protected from torn writes.

Therefore, this commit makes XLOG_FPI_FOR_HINT records honor full_page_writes
setting. That is, XLOG_FPI_FOR_HINT records may include no full-page images
if full_page_writes is disabled, and WAL replay of them does nothing.

Reported-by: Zhang Wenjie
Author: Kyotaro Horiguchi
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/[email protected]

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2ee951513928839252a8175e7d920cd3a9f135a3..3479402272bf801844188c6065ddf0de5e6c45b8 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -10148,7 +10148,10 @@ xlog_redo(XLogReaderState *record)
    uint8       info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
    XLogRecPtr  lsn = record->EndRecPtr;
 
-   /* in XLOG rmgr, backup blocks are only used by XLOG_FPI records */
+   /*
+    * In XLOG rmgr, backup blocks are only used by XLOG_FPI and
+    * XLOG_FPI_FOR_HINT records.
+    */
    Assert(info == XLOG_FPI || info == XLOG_FPI_FOR_HINT ||
           !XLogRecHasAnyBlockRefs(record));
 
@@ -10356,25 +10359,32 @@ xlog_redo(XLogReaderState *record)
    else if (info == XLOG_FPI || info == XLOG_FPI_FOR_HINT)
    {
        /*
-        * Full-page image (FPI) records contain nothing else but a backup
-        * block (or multiple backup blocks). Every block reference must
-        * include a full-page image - otherwise there would be no point in
-        * this record.
+        * XLOG_FPI records contain nothing else but one or more block
+        * references. Every block reference must include a full-page image
+        * even if full_page_writes was disabled when the record was generated
+        * - otherwise there would be no point in this record.
+        *
+        * XLOG_FPI_FOR_HINT records are generated when a page needs to be
+        * WAL-logged because of a hint bit update. They are only generated
+        * when checksums and/or wal_log_hints are enabled. They may include
+        * no full-page images if full_page_writes was disabled when they were
+        * generated. In this case there is nothing to do here.
         *
         * No recovery conflicts are generated by these generic records - if a
         * resource manager needs to generate conflicts, it has to define a
         * separate WAL record type and redo routine.
-        *
-        * XLOG_FPI_FOR_HINT records are generated when a page needs to be
-        * WAL- logged because of a hint bit update. They are only generated
-        * when checksums are enabled. There is no difference in handling
-        * XLOG_FPI and XLOG_FPI_FOR_HINT records, they use a different info
-        * code just to distinguish them for statistics purposes.
         */
        for (uint8 block_id = 0; block_id <= record->max_block_id; block_id++)
        {
            Buffer      buffer;
 
+           if (!XLogRecHasBlockImage(record, block_id))
+           {
+               if (info == XLOG_FPI)
+                   elog(ERROR, "XLOG_FPI record did not contain a full-page image");
+               continue;
+           }
+
            if (XLogReadBufferForRedo(record, block_id, &buffer) != BLK_RESTORED)
                elog(ERROR, "unexpected XLogReadBufferForRedo result when restoring backup block");
            UnlockReleaseBuffer(buffer);

diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
index 3d2c9c3e8cf529279e0c6e40949b331a1ae7a346..e596a0470a9775ffa63d3171d8889a1a9a0ca1ed 100644 (file)
--- a/src/backend/access/transam/xloginsert.c
+++ b/src/backend/access/transam/xloginsert.c
@@ -287,8 +287,6 @@ XLogRegisterBlock(uint8 block_id, RelFileNode *rnode, ForkNumber forknum,
 {
    registered_buffer *regbuf;
 
-   /* This is currently only used to WAL-log a full-page image of a page */
-   Assert(flags & REGBUF_FORCE_IMAGE);
    Assert(begininsert_called);
 
    if (block_id >= max_registered_block_id)
@@ -995,7 +993,7 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
 
    if (lsn <= RedoRecPtr)
    {
-       int         flags;
+       int         flags = 0;
        PGAlignedBlock copied_buffer;
        char       *origdata = (char *) BufferGetBlock(buffer);
        RelFileNode rnode;
@@ -1022,7 +1020,6 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
 
        XLogBeginInsert();
 
-       flags = REGBUF_FORCE_IMAGE;
        if (buffer_std)
            flags |= REGBUF_STANDARD;