branches/zip: Maintain a valid checksum for compressed-only pages kept in

the buffer pool.

buf_LRU_free_block(): When preserving the compressed page, compute the
checksum.  Also assert page_zip_validate().

buf_zip_decompress(): Add parameter "check" for enabling checksum tests.
Before decompressing a compressed-only page from the buffer pool, verify
the compressed page checksum.

buf/buf0buf.c

@@ -1982,13 +1982,31 @@ ibool
 buf_zip_decompress(
 /*===============*/
 				/* out: TRUE if successful */
-	buf_block_t*	block)	/* in/out: block */
+	buf_block_t*	block,	/* in/out: block */
+	ibool		check)	/* in: TRUE=verify the page checksum */
 {
 	const byte* frame = block->page.zip.data;
 
 	ut_ad(buf_block_get_zip_size(block));
 	ut_a(buf_block_get_space(block) != 0);
 
+	if (UNIV_LIKELY(check)) {
+		ulint	stamp_checksum	= mach_read_from_4(
+			frame + FIL_PAGE_SPACE_OR_CHKSUM);
+		ulint	calc_checksum	= page_zip_calc_checksum(
+			frame, page_zip_get_size(&block->page.zip));
+
+		if (UNIV_UNLIKELY(stamp_checksum != calc_checksum)) {
+			ut_print_timestamp(stderr);
+			fprintf(stderr,
+				"  InnoDB: compressed page checksum mismatch"
+				" (space %u page %u): %lu != %lu\n",
+				block->page.space, block->page.offset,
+				stamp_checksum, calc_checksum);
+			return(FALSE);
+		}
+	}
+
 	switch (fil_page_get_type(frame)) {
 	case FIL_PAGE_INDEX:
 		if (page_zip_decompress(&block->page.zip,
@@ -2016,7 +2034,7 @@ buf_zip_decompress(
 
 	ut_print_timestamp(stderr);
 	fprintf(stderr,
-		"InnoDB: unknown compressed page"
+		"  InnoDB: unknown compressed page"
 		" type %lu\n",
 		fil_page_get_type(frame));
 	return(FALSE);
@@ -2146,7 +2164,7 @@ buf_page_init_for_read(
 				mtr_commit(&mtr);
 			}
 
-			buf_zip_decompress(block);
+			buf_zip_decompress(block, srv_use_checksums);
 
 			return(NULL);
 		case BUF_BLOCK_FILE_PAGE:
@@ -2361,7 +2379,7 @@ buf_page_io_complete(
 		if (buf_block_get_zip_size(block)) {
 			frame = block->page.zip.data;
 
-			if (!buf_zip_decompress(block)) {
+			if (!buf_zip_decompress(block, FALSE)) {
 
 				goto corrupt;
 			}

buf/buf0lru.c

@@ -922,6 +922,25 @@ buf_LRU_free_block(
 		btr_search_drop_page_hash_index((buf_block_t*) bpage);
 		ut_a(bpage->buf_fix_count == 0);
 
+		if (bpage->zip.data && UNIV_LIKELY(srv_use_checksums)) {
+			/* Compute and stamp the compressed page
+			checksum while not holding any mutex.  The
+			block is already half-freed
+			(BUF_BLOCK_REMOVE_HASH) and removed from
+			buf_pool->page_hash, thus inaccessible by any
+			other thread. */
+#ifdef UNIV_ZIP_DEBUG
+			ut_a(page_zip_validate(&bpage->zip,
+					       ((buf_block_t*) bpage)->frame));
+#endif /* UNIV_ZIP_DEBUG */
+
+			mach_write_to_4(
+				bpage->zip.data + FIL_PAGE_SPACE_OR_CHKSUM,
+				page_zip_calc_checksum(
+					bpage->zip.data,
+					page_zip_get_size(&bpage->zip)));
+		}
+
 		mutex_enter(&(buf_pool->mutex));
 
 		if (bpage->zip.data) {