branches/zip: buf_flush_write_block_low(): Avoid recomputing the compressed

page checksum of compressed-only blocks.  Pass the compressed page frame
to fil_io() when needed.

page_zip_calc_checksum(): Skip also FIL_PAGE_LSN and FIL_PAGE_FILE_FLUSH_LSN.

buf_flush_init_for_writing(): Expect page to be non-NULL.

buf/buf0flu.c

@@ -601,12 +601,13 @@ Initializes a page for writing to the tablespace. */
 void
 buf_flush_init_for_writing(
 /*=======================*/
-	byte*		page,		/* in/out: page, may be NULL
-					if page_zip_ is non-NULL */
+	byte*		page,		/* in/out: page */
 	void*		page_zip_,	/* in/out: compressed page, or NULL */
 	ib_uint64_t	newest_lsn)	/* in: newest modification lsn
 					to the page */
 {
+	ut_ad(page);
+
 	if (page_zip_) {
 		page_zip_des_t*	page_zip = page_zip_;
 		ulint		zip_size = page_zip_get_size(page_zip);
@@ -614,18 +615,14 @@ buf_flush_init_for_writing(
 		ut_ad(ut_is_2pow(zip_size));
 		ut_ad(zip_size <= UNIV_PAGE_SIZE);
 
-		switch (UNIV_EXPECT(fil_page_get_type(page
-						      ? page : page_zip->data),
-				    FIL_PAGE_INDEX)) {
+		switch (UNIV_EXPECT(fil_page_get_type(page), FIL_PAGE_INDEX)) {
 		case FIL_PAGE_TYPE_ALLOCATED:
 		case FIL_PAGE_INODE:
 		case FIL_PAGE_IBUF_BITMAP:
 		case FIL_PAGE_TYPE_FSP_HDR:
 		case FIL_PAGE_TYPE_XDES:
 			/* These are essentially uncompressed pages. */
-			if (page) {
-				memcpy(page_zip->data, page, zip_size);
-			}
+			memcpy(page_zip->data, page, zip_size);
 			/* fall through */
 		case FIL_PAGE_TYPE_ZBLOB:
 		case FIL_PAGE_INDEX:
@@ -644,8 +641,6 @@ buf_flush_init_for_writing(
 		ut_error;
 	}
 
-	ut_ad(page);
-
 	/* Write the newest modification lsn to the page header and trailer */
 	mach_write_ull(page + FIL_PAGE_LSN, newest_lsn);
 
@@ -715,22 +710,24 @@ buf_flush_write_block_low(
 		ut_error;
 		break;
 	case BUF_BLOCK_ZIP_DIRTY:
+		frame = bpage->zip.data;
 		if (UNIV_LIKELY(srv_use_checksums)) {
-			ut_a(mach_read_from_4(bpage->zip.data
-					      + FIL_PAGE_SPACE_OR_CHKSUM)
-			     == page_zip_calc_checksum(bpage->zip.data,
-						       zip_size));
+			ut_a(mach_read_from_4(frame + FIL_PAGE_SPACE_OR_CHKSUM)
+			     == page_zip_calc_checksum(frame, zip_size));
 		}
+		mach_write_ull(frame + FIL_PAGE_LSN,
+			       bpage->newest_modification);
+		memset(frame + FIL_PAGE_FILE_FLUSH_LSN, 0, 8);
 		break;
 	case BUF_BLOCK_FILE_PAGE:
 		frame = ((buf_block_t*) bpage)->frame;
+		buf_flush_init_for_writing(frame,
+					   bpage->zip.data
+					   ? &bpage->zip : NULL,
+					   bpage->newest_modification);
 		break;
 	}
 
-	buf_flush_init_for_writing(frame,
-				   bpage->zip.data ? &bpage->zip : NULL,
-				   bpage->newest_modification);
-
 	if (!srv_use_doublewrite_buf || !trx_doublewrite) {
 		fil_io(OS_FILE_WRITE | OS_AIO_SIMULATED_WAKE_LATER,
 		       FALSE, buf_page_get_space(bpage), zip_size,

include/buf0flu.h

@@ -48,8 +48,7 @@ Initializes a page for writing to the tablespace. */
 void
 buf_flush_init_for_writing(
 /*=======================*/
-	byte*		page,		/* in/out: page, may be NULL
-					if page_zip_ is non-NULL */
+	byte*		page,		/* in/out: page */
 	void*		page_zip_,	/* in/out: compressed page, or NULL */
 	ib_uint64_t	newest_lsn);	/* in: newest modification lsn
 					to the page */

page/page0zip.c

@@ -3729,8 +3729,19 @@ page_zip_calc_checksum(
 	const void*	data,	/* in: compressed page */
 	ulint		size)	/* in: size of compressed page */
 {
-	/* Exclude the 32-bit checksum field from the checksum. */
-	return((ulint) adler32(0,
-			       ((const Bytef*) data) + FIL_PAGE_OFFSET,
-			       size - FIL_PAGE_OFFSET));
+	/* Exclude FIL_PAGE_SPACE_OR_CHKSUM, FIL_PAGE_LSN,
+	and FIL_PAGE_FILE_FLUSH_LSN from the checksum. */
+
+	const Bytef*	s	= data;
+	uLong		adler;
+
+	ut_ad(size > FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID);
+
+	adler = adler32(0L, s + FIL_PAGE_OFFSET,
+			FIL_PAGE_LSN - FIL_PAGE_OFFSET);
+	adler = adler32(adler, s + FIL_PAGE_TYPE, 2);
+	adler = adler32(adler, s + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID,
+			size - FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID);
+
+	return((ulint) adler);
 }