Correctly align page's images in generic wal API

Page image should be MAXALIGN'ed because existing code could directly align
pointers in page instead of align offset from beginning of page.

Found during play with indexes as extenstion, Alexander Korotkov and me

diff --git a/src/backend/access/transam/generic_xlog.c b/src/backend/access/transam/generic_xlog.c
index 6e213e2f60c9ba3f87581836b0c6ee763157d62d..8ad69f83b1f74caee11b357c891eac0cd481cc1d 100644 (file)
--- a/src/backend/access/transam/generic_xlog.c
+++ b/src/backend/access/transam/generic_xlog.c
@@ -52,7 +52,9 @@ typedef struct
        Buffer          buffer;                 /* registered buffer */
        int                     flags;                  /* flags for this buffer */
        int                     deltaLen;               /* space consumed in delta field */
-       char            image[BLCKSZ];  /* copy of page image for modification */
+       char            *image;                 /* copy of page image for modification,
+                                                                * do not do it in-place to have aligned
+                                                                * memory chunk */
        char            delta[MAX_DELTA_SIZE];  /* delta between page images */
 } PageData;
 
@@ -268,7 +270,15 @@ GenericXLogStart(Relation relation)
 
        state->isLogged = RelationNeedsWAL(relation);
        for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+       {
+               /*
+                * pre-alloc page's images to prevent allocation in
+                * GenericXLogRegisterBuffer() which could be called in different
+                * memory context(s)
+                */
+               state->pages[i].image = palloc(BLCKSZ);
                state->pages[i].buffer = InvalidBuffer;
+       }
 
        return state;
 }
@@ -422,6 +432,8 @@ GenericXLogFinish(GenericXLogState *state)
                lsn = InvalidXLogRecPtr;
        }
 
+       for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+               pfree(state->pages[i].image);
        pfree(state);
 
        return lsn;