Faster PageIsVerified() for the all zeroes case.

That's primarily useful for testing very large relations, using sparse
files.

Discussion: <20140331101001.GE13135@alap3.anarazel.de>
Reviewed-By: Peter Geoghegan

diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index f2a07f211165205aae20f1e22c0039fc6adfcc93..1b70bfbe8cc1953616a634282463fb02749b70e8 100644 (file)
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -81,7 +81,7 @@ bool
 PageIsVerified(Page page, BlockNumber blkno)
 {
        PageHeader      p = (PageHeader) page;
-       char       *pagebytes;
+       size_t     *pagebytes;
        int                     i;
        bool            checksum_failure = false;
        bool            header_sane = false;
@@ -118,10 +118,17 @@ PageIsVerified(Page page, BlockNumber blkno)
                        return true;
        }
 
-       /* Check all-zeroes case */
+       /*
+        * Check all-zeroes case. Luckily BLCKSZ is guaranteed to always be a
+        * multiple of size_t - and it's much faster to compare memory using the
+        * native word size.
+        */
+       StaticAssertStmt(BLCKSZ == (BLCKSZ / sizeof(size_t)) * sizeof(size_t),
+                                        "BLCKSZ has to be a multiple of sizeof(size_t)");
+
        all_zeroes = true;
-       pagebytes = (char *) page;
-       for (i = 0; i < BLCKSZ; i++)
+       pagebytes = (size_t *) page;
+       for (i = 0; i < (BLCKSZ / sizeof(size_t)); i++)
        {
                if (pagebytes[i] != 0)
                {