branches/zip: Replace FIL_PAGE_ZBLOB_SPACE_ID and FIL_PAGE_ZBLOB_DATA

with FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID and FIL_PAGE_DATA.  The doublewrite
buffer needs to read the space_id in order to determine the type of the page.
Because FIL_PAGE_TYPE could contain garbage in MySQL/InnoDB 5.0 and earlier
versions, we cannot trust fil_page_get_type().  Instead, we have to always
store the space_id at the same location.  This modification wastes 12 bytes
per compressed BLOB page (1.2% on 1-kilobyte pages).

btr/btr0cur.c

@@ -3722,9 +3722,9 @@ btr_store_big_rec_extern_fields(
 						FIL_PAGE_TYPE_ZBLOB);
 
 				c_stream.next_out = page
-					+ FIL_PAGE_ZBLOB_DATA;
+					+ FIL_PAGE_DATA;
 				c_stream.avail_out = page_zip->size
-					- FIL_PAGE_ZBLOB_DATA;
+					- FIL_PAGE_DATA;
 
 				err = deflate(&c_stream, Z_FINISH);
 				ut_a(err == Z_OK || err == Z_STREAM_END);
@@ -3734,6 +3734,9 @@ btr_store_big_rec_extern_fields(
 				/* Write the "next BLOB page" pointer */
 				mlog_write_ulint(page + FIL_PAGE_NEXT,
 						 FIL_NULL, MLOG_4BYTES, &mtr);
+				/* Initialize the unused "prev page" pointer */
+				mlog_write_ulint(page + FIL_PAGE_PREV,
+						 FIL_NULL, MLOG_4BYTES, &mtr);
 				/* Zero out the unused part of the page. */
 				memset(page + page_zip->size
 				       - c_stream.avail_out,
@@ -4204,7 +4207,7 @@ btr_copy_externally_stored_field_prefix_low(
 				/* When the BLOB begins at page header,
 				the compressed data payload does not
 				immediately follow the next page pointer. */
-				offset = FIL_PAGE_ZBLOB_DATA;
+				offset = FIL_PAGE_DATA;
 			} else {
 				offset += 4;
 			}

buf/buf0buf.c

@@ -450,7 +450,8 @@ buf_page_print(
 				(ulong) mach_read_from_4(
 					read_buf + FIL_PAGE_OFFSET),
 				(ulong) mach_read_from_4(
-					read_buf + FIL_PAGE_ZBLOB_SPACE_ID));
+					read_buf
+					+ FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID));
 			return;
 		default:
 			ut_print_timestamp(stderr);
@@ -1980,15 +1981,8 @@ buf_page_io_complete(
 		doublewrite buffer, then the page number and space id
 		should be the same as in block. */
 		read_page_no = mach_read_from_4(frame + FIL_PAGE_OFFSET);
-		switch (fil_page_get_type(frame)) {
-		case FIL_PAGE_TYPE_ZBLOB:
-			read_space_id = mach_read_from_4(
-				frame + FIL_PAGE_ZBLOB_SPACE_ID);
-			break;
-		default:
-			read_space_id = mach_read_from_4(
-				frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID);
-		}
+		read_space_id = mach_read_from_4(
+			frame + FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID);
 
 		if (!block->space
 		    && trx_doublewrite_page_inside(block->offset)) {

buf/buf0flu.c

@@ -515,22 +515,6 @@ buf_flush_init_for_writing(
 		ut_ad(zip_size <= UNIV_PAGE_SIZE);
 
 		switch (UNIV_EXPECT(fil_page_get_type(page), FIL_PAGE_INDEX)) {
-		case FIL_PAGE_TYPE_ZBLOB:
-			ut_ad(fil_page_get_type(page_zip->data)
-			      == FIL_PAGE_TYPE_ZBLOB);
-			mach_write_to_4(page_zip->data
-					+ FIL_PAGE_OFFSET, page_no);
-			mach_write_to_4(page_zip->data
-					+ FIL_PAGE_ZBLOB_SPACE_ID, space);
-			mach_write_to_8(page_zip->data
-					+ FIL_PAGE_LSN, newest_lsn);
-			mach_write_to_4(page_zip->data
-					+ FIL_PAGE_SPACE_OR_CHKSUM,
-					srv_use_checksums
-					? page_zip_calc_checksum(
-						page_zip->data, zip_size)
-					: BUF_NO_CHECKSUM_MAGIC);
-			return;
 		case FIL_PAGE_TYPE_ALLOCATED:
 		case FIL_PAGE_INODE:
 		case FIL_PAGE_IBUF_BITMAP:
@@ -539,6 +523,7 @@ buf_flush_init_for_writing(
 			/* These are essentially uncompressed pages. */
 			memcpy(page_zip->data, page, zip_size);
 			/* fall through */
+		case FIL_PAGE_TYPE_ZBLOB:
 		case FIL_PAGE_INDEX:
 			mach_write_to_4(page
 					+ FIL_PAGE_OFFSET, page_no);

include/fil0fil.h

@@ -62,8 +62,6 @@ extern fil_addr_t	fil_addr_null;
 					This field is not set on BLOB pages,
 					which are stored as a singly-linked
 					list.  See also FIL_PAGE_NEXT. */
-#define FIL_PAGE_ZBLOB_SPACE_ID	8	/* space id of a compressed BLOB page,
-					4 bytes */
 #define FIL_PAGE_NEXT		12	/* if there is a 'natural' successor
 					of the page, its offset.
 					Otherwise FIL_NULL.
@@ -95,8 +93,6 @@ extern fil_addr_t	fil_addr_null;
 					first page in a data file: the file
 					has been flushed to disk at least up
 					to this lsn */
-#define FIL_PAGE_ZBLOB_DATA	26	/* start of data stream on a
-					FIL_PAGE_TYPE_ZBLOB page */
 #define FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID  34 /* starting from 4.1.x this
 					contains the space id of the page */
 #define FIL_PAGE_DATA		38	/* start of the data on the page */