branches/zip: Undo r2079 and fix the cause of uninitialized data bytes

in page_zip_decompress().

page_zip_decompress_clust(), page_zip_decompress_clust_ext(): Zero-fill
the columns DB_TRX_ID and DB_ROLL_PTR on the uncompressed page.

page/page0zip.c

@@ -2165,6 +2165,11 @@ page_zip_decompress_clust_ext(
 
 			ut_ad(d_stream->next_out == dst);
 
+			/* Clear DB_TRX_ID and DB_ROLL_PTR in order to
+			avoid uninitialized bytes in case the record
+			is affected by page_zip_apply_log(). */
+			memset(dst, 0, DATA_TRX_ID_LEN + DATA_ROLL_PTR_LEN);
+
 			d_stream->next_out += DATA_TRX_ID_LEN
 				+ DATA_ROLL_PTR_LEN;
 		} else if (rec_offs_nth_extern(offsets, i)) {
@@ -2329,6 +2334,11 @@ page_zip_decompress_clust(
 
 			ut_ad(d_stream->next_out == dst);
 
+			/* Clear DB_TRX_ID and DB_ROLL_PTR in order to
+			avoid uninitialized bytes in case the record
+			is affected by page_zip_apply_log(). */
+			memset(dst, 0, DATA_TRX_ID_LEN + DATA_ROLL_PTR_LEN);
+
 			d_stream->next_out += DATA_TRX_ID_LEN
 				+ DATA_ROLL_PTR_LEN;
 		}
@@ -2505,15 +2515,9 @@ page_zip_decompress(
 	recs = mem_heap_alloc(heap, n_dense * (2 * sizeof *recs));
 
 #ifdef UNIV_ZIP_DEBUG
-	/* Clear the page.  The fill byte used to be 0x55, but we use
-	0 from now on in order to mask a known discrepancy: When a
-	record is freed (i.e., delete-marked and deleted), a shorter
-	record is allocated from the space, and the page is
-	compressed, the unused bytes after the shorter record will not
-	be initialized by the decompressor. */
-	memset(page, 0, UNIV_PAGE_SIZE);
+	/* Clear the page. */
+	memset(page, 0x55, UNIV_PAGE_SIZE);
 #endif /* UNIV_ZIP_DEBUG */
-	/* To avoid bogus warnings, use UNIV_MEM_VALID instead.  See above. */
 	UNIV_MEM_INVALID(page, UNIV_PAGE_SIZE);
 	/* Copy the page header. */
 	memcpy(page, page_zip->data, PAGE_DATA);