branches/zip bug# 49535

This is a backport of r4924.
mem_heap_get_size() scans all allocated blocks to calculate the total
size of the heap. This patch introduces a new, total_size, field in
mem_block_info_struct. This field is valid only for base block 
(i.e.: the first block allocated for the heap) and is set to
ULINT_UNDEFINED in other blocks.
This considerably improves the performance of redo scan during recovery.

rb://108 issue#216

Approved by: Heikki

------------------------------------------------------------------------

include/mem0mem.h

@@ -359,6 +359,9 @@ struct mem_block_info_struct {
 			to the heap is also the first block in this list,
 			though it also contains the base node of the list. */
 	ulint	len;	/*!< physical length of this block in bytes */
+	ulint	total_size; /* physical length in bytes of all blocks
+			in the heap. This is defined only in the base
+			node and is set to ULINT_UNDEFINED in others. */
 	ulint	type;	/*!< type of heap: MEM_HEAP_DYNAMIC, or
 			MEM_HEAP_BUF possibly ORed to MEM_HEAP_BTR_SEARCH */
 	ulint	free;	/*!< offset in bytes of the first free position for

include/mem0mem.ic

@@ -579,18 +579,12 @@ mem_heap_get_size(
 /*==============*/
 	mem_heap_t*	heap)	/*!< in: heap */
 {
-	mem_block_t*	block;
 	ulint		size	= 0;
 
 	ut_ad(mem_heap_check(heap));
 
-	block = heap;
-
-	while (block != NULL) {
+	size = heap->total_size;
 
-		size += mem_block_get_len(block);
-		block = UT_LIST_GET_NEXT(list, block);
-	}
 #ifndef UNIV_HOTBACKUP
 	if (heap->free_block) {
 		size += UNIV_PAGE_SIZE;

mem/mem0mem.c

@@ -383,6 +383,20 @@ mem_heap_create_block(
 	mem_block_set_free(block, MEM_BLOCK_HEADER_SIZE);
 	mem_block_set_start(block, MEM_BLOCK_HEADER_SIZE);
 
+	if (UNIV_UNLIKELY(heap == NULL)) {
+		/* This is the first block of the heap. The field
+		total_size should be initialized here */
+		block->total_size = len;
+	} else {
+		/* Not the first allocation for the heap. This block's
+		total_length field should be set to undefined. */
+		ut_d(block->total_size = ULINT_UNDEFINED);
+		UNIV_MEM_INVALID(&block->total_size,
+				 sizeof block->total_size);
+
+		heap->total_size += len;
+	}
+
 	ut_ad((ulint)MEM_BLOCK_HEADER_SIZE < len);
 
 	return(block);
@@ -471,6 +485,10 @@ mem_heap_block_free(
 
 	mem_pool_mutex_exit();
 #endif
+
+	ut_ad(heap->total_size >= block->len);
+	heap->total_size -= block->len;
+
 	type = heap->type;
 	len = block->len;
 	block->magic_n = MEM_FREED_BLOCK_MAGIC_N;