Reduce buffer pool mutex contention under >= 4 big concurrent

CPU-bound SELECT queries.  (Bug #15815)

Fix: replace the mutex by one mutex protecting the 'flush list'
(and the free list) and several mutexes protecting portions of the
buffer pool, where we keep several indivudual LRU lists of pages.

This patch is from Sunny Bains and Heikki Tuuri.

buf/buf0buf.c

@@ -221,6 +221,9 @@ in the free list to the frames.
 5) When we have AWE enabled, we disable adaptive hash indexes.
 */
 
+/* Value in microseconds */
+static const int WAIT_FOR_READ	= 20000;
+
 buf_pool_t*	buf_pool = NULL; /* The buffer buf_pool of the database */
 
 #ifdef UNIV_DEBUG
@@ -539,6 +542,8 @@ buf_block_init(
 
 	block->n_pointers = 0;
 
+	mutex_create(&block->mutex, SYNC_BUF_BLOCK);
+
 	rw_lock_create(&block->lock, SYNC_LEVEL_VARYING);
 	ut_ad(rw_lock_validate(&(block->lock)));
 
@@ -813,8 +818,15 @@ buf_awe_map_page_to_frame(
 	bck = UT_LIST_GET_LAST(buf_pool->awe_LRU_free_mapped);
 
 	while (bck) {
-		if (bck->state == BUF_BLOCK_FILE_PAGE
-		    && (bck->buf_fix_count != 0 || bck->io_fix != 0)) {
+		ibool skip;
+
+		mutex_enter(&bck->mutex);
+
+		skip = (bck->state == BUF_BLOCK_FILE_PAGE
+			&& (bck->buf_fix_count != 0 || bck->io_fix != 0));
+
+		if (skip) {
+			mutex_exit(&bck->mutex);
 
 			/* We have to skip this */
 			bck = UT_LIST_GET_PREV(awe_LRU_free_mapped, bck);
@@ -848,6 +860,8 @@ buf_awe_map_page_to_frame(
 
 			buf_pool->n_pages_awe_remapped++;
 
+			mutex_exit(&bck->mutex);
+
 			return;
 		}
 	}
@@ -886,13 +900,22 @@ buf_block_make_young(
 /*=================*/
 	buf_block_t*	block)	/* in: block to make younger */
 {
+#ifdef UNIV_SYNC_DEBUG
+	ut_ad(!mutex_own(&(buf_pool->mutex)));
+#endif /* UNIV_SYNC_DEBUG */
+
+	/* Note that we read freed_page_clock's without holding any mutex:
+	this is allowed since the result is used only in heuristics */
+
 	if (buf_pool->freed_page_clock >= block->freed_page_clock
-	    + 1 + (buf_pool->curr_size / 1024)) {
+				+ 1 + (buf_pool->curr_size / 4)) {
 
+		mutex_enter(&buf_pool->mutex);
 		/* There has been freeing activity in the LRU list:
 		best to move to the head of the LRU list */
 
 		buf_LRU_make_block_young(block);
+		mutex_exit(&buf_pool->mutex);
 	}
 }
 
@@ -927,12 +950,16 @@ buf_block_free(
 /*===========*/
 	buf_block_t*	block)	/* in, own: block to be freed */
 {
-	ut_a(block->state != BUF_BLOCK_FILE_PAGE);
-
 	mutex_enter(&(buf_pool->mutex));
 
+	mutex_enter(&block->mutex);
+
+	ut_a(block->state != BUF_BLOCK_FILE_PAGE);
+
 	buf_LRU_block_free_non_file_page(block);
 
+	mutex_exit(&block->mutex);
+
 	mutex_exit(&(buf_pool->mutex));
 }
 
@@ -1151,9 +1178,8 @@ buf_page_get_gen(
 #endif
 	buf_pool->n_page_gets++;
 loop:
-	mutex_enter_fast(&(buf_pool->mutex));
-
 	block = NULL;
+	mutex_enter_fast(&(buf_pool->mutex));
 
 	if (guess) {
 		block = buf_block_align(guess);
@@ -1191,6 +1217,8 @@ loop:
 		goto loop;
 	}
 
+	mutex_enter(&block->mutex);
+
 	ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 
 	must_read = FALSE;
@@ -1200,9 +1228,9 @@ loop:
 		must_read = TRUE;
 
 		if (mode == BUF_GET_IF_IN_POOL) {
-
 			/* The page is only being read to buffer */
-			mutex_exit(&(buf_pool->mutex));
+			mutex_exit(&buf_pool->mutex);
+			mutex_exit(&block->mutex);
 
 			return(NULL);
 		}
@@ -1226,7 +1254,7 @@ loop:
 #else
 	buf_block_buf_fix_inc(block);
 #endif
-	buf_block_make_young(block);
+	mutex_exit(&buf_pool->mutex);
 
 	/* Check if this is the first access to the page */
 
@@ -1234,10 +1262,13 @@ loop:
 
 	block->accessed = TRUE;
 
+	mutex_exit(&block->mutex);
+
+	buf_block_make_young(block);
+
 #ifdef UNIV_DEBUG_FILE_ACCESSES
 	ut_a(block->file_page_was_freed == FALSE);
 #endif
-	mutex_exit(&(buf_pool->mutex));
 
 #ifdef UNIV_DEBUG
 	buf_dbg_counter++;
@@ -1262,13 +1293,14 @@ loop:
 		}
 
 		if (!success) {
-			mutex_enter(&(buf_pool->mutex));
+			mutex_enter(&block->mutex);
 
 			block->buf_fix_count--;
+
+			mutex_exit(&block->mutex);
 #ifdef UNIV_SYNC_DEBUG
 			rw_lock_s_unlock(&(block->debug_latch));
 #endif
-			mutex_exit(&(buf_pool->mutex));
 
 			return(NULL);
 		}
@@ -1279,18 +1311,16 @@ loop:
 			completes */
 
 			for (;;) {
-				mutex_enter(&(buf_pool->mutex));
+				mutex_enter(&block->mutex);
 
 				if (block->io_fix == BUF_IO_READ) {
 
-					mutex_exit(&(buf_pool->mutex));
-
-					/* Sleep 20 milliseconds */
+					mutex_exit(&block->mutex);
 
-					os_thread_sleep(20000);
+					os_thread_sleep(WAIT_FOR_READ);
 				} else {
 
-					mutex_exit(&(buf_pool->mutex));
+					mutex_exit(&block->mutex);
 
 					break;
 				}
@@ -1349,14 +1379,14 @@ buf_page_optimistic_get_func(
 	ut_ad(mtr && block);
 	ut_ad((rw_latch == RW_S_LATCH) || (rw_latch == RW_X_LATCH));
 
-	mutex_enter(&(buf_pool->mutex));
-
 	/* If AWE is used, block may have a different frame now, e.g., NULL */
 
+	mutex_enter(&block->mutex);
+
 	if (UNIV_UNLIKELY(block->state != BUF_BLOCK_FILE_PAGE)
 	    || UNIV_UNLIKELY(block->frame != guess)) {
-exit_func:
-		mutex_exit(&(buf_pool->mutex));
+
+		mutex_exit(&block->mutex);
 
 		return(FALSE);
 	}
@@ -1366,15 +1396,14 @@ exit_func:
 #else
 	buf_block_buf_fix_inc(block);
 #endif
-	buf_block_make_young(block);
-
-	/* Check if this is the first access to the page */
-
 	accessed = block->accessed;
-
 	block->accessed = TRUE;
 
-	mutex_exit(&(buf_pool->mutex));
+	mutex_exit(&block->mutex);
+
+	buf_block_make_young(block);
+
+	/* Check if this is the first access to the page */
 
 	ut_ad(!ibuf_inside() || ibuf_page(block->space, block->offset));
 
@@ -1389,13 +1418,16 @@ exit_func:
 	}
 
 	if (UNIV_UNLIKELY(!success)) {
-		mutex_enter(&(buf_pool->mutex));
+		mutex_enter(&block->mutex);
 
 		block->buf_fix_count--;
+
+		mutex_exit(&block->mutex);
+
 #ifdef UNIV_SYNC_DEBUG
 		rw_lock_s_unlock(&(block->debug_latch));
 #endif
-		goto exit_func;
+		return(FALSE);
 	}
 
 	if (UNIV_UNLIKELY(!UT_DULINT_EQ(modify_clock, block->modify_clock))) {
@@ -1408,13 +1440,16 @@ exit_func:
 			rw_lock_x_unlock(&(block->lock));
 		}
 
-		mutex_enter(&(buf_pool->mutex));
+		mutex_enter(&block->mutex);
 
 		block->buf_fix_count--;
+
+		mutex_exit(&block->mutex);
+
 #ifdef UNIV_SYNC_DEBUG
 		rw_lock_s_unlock(&(block->debug_latch));
 #endif
-		goto exit_func;
+		return(FALSE);
 	}
 
 	mtr_memo_push(mtr, block, fix_type);
@@ -1471,10 +1506,10 @@ buf_page_get_known_nowait(
 	ut_ad(mtr);
 	ut_ad((rw_latch == RW_S_LATCH) || (rw_latch == RW_X_LATCH));
 
-	mutex_enter(&(buf_pool->mutex));
-
 	block = buf_block_align(guess);
 
+	mutex_enter(&block->mutex);
+
 	if (block->state == BUF_BLOCK_REMOVE_HASH) {
 		/* Another thread is just freeing the block from the LRU list
 		of the buffer pool: do not try to access this page; this
@@ -1483,7 +1518,7 @@ buf_page_get_known_nowait(
 		we have already removed it from the page address hash table
 		of the buffer pool. */
 
-		mutex_exit(&(buf_pool->mutex));
+		mutex_exit(&block->mutex);
 
 		return(FALSE);
 	}
@@ -1495,12 +1530,12 @@ buf_page_get_known_nowait(
 #else
 	buf_block_buf_fix_inc(block);
 #endif
+	mutex_exit(&block->mutex);
+
 	if (mode == BUF_MAKE_YOUNG) {
 		buf_block_make_young(block);
 	}
 
-	mutex_exit(&(buf_pool->mutex));
-
 	ut_ad(!ibuf_inside() || (mode == BUF_KEEP_OLD));
 
 	if (rw_latch == RW_S_LATCH) {
@@ -1514,13 +1549,15 @@ buf_page_get_known_nowait(
 	}
 
 	if (!success) {
-		mutex_enter(&(buf_pool->mutex));
+		mutex_enter(&block->mutex);
 
 		block->buf_fix_count--;
+
+		mutex_exit(&block->mutex);
+
 #ifdef UNIV_SYNC_DEBUG
 		rw_lock_s_unlock(&(block->debug_latch));
 #endif
-		mutex_exit(&(buf_pool->mutex));
 
 		return(FALSE);
 	}
@@ -1568,7 +1605,6 @@ buf_page_init_for_backup_restore(
 	block->offset		= offset;
 
 	block->lock_hash_val	= 0;
-	block->lock_mutex	= NULL;
 
 	block->freed_page_clock = 0;
 
@@ -1601,6 +1637,7 @@ buf_page_init(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&(block->mutex)));
 #endif /* UNIV_SYNC_DEBUG */
 	ut_a(block->state != BUF_BLOCK_FILE_PAGE);
 
@@ -1615,7 +1652,6 @@ buf_page_init(
 	block->index		= NULL;
 
 	block->lock_hash_val	= lock_rec_hash(space, offset);
-	block->lock_mutex	= NULL;
 
 	/* Insert into the hash table of file pages */
 
@@ -1709,6 +1745,7 @@ buf_page_init_for_read(
 	ut_a(block);
 
 	mutex_enter(&(buf_pool->mutex));
+	mutex_enter(&block->mutex);
 
 	if (fil_tablespace_deleted_or_being_deleted_in_mem(
 		    space, tablespace_version)) {
@@ -1722,7 +1759,9 @@ buf_page_init_for_read(
 		    deleted or is being deleted, or the page is
 		    already in buf_pool, return */
 
+		mutex_exit(&block->mutex);
 		    mutex_exit(&(buf_pool->mutex));
+
 		    buf_block_free(block);
 
 		    if (mode == BUF_READ_IBUF_PAGES_ONLY) {
@@ -1742,6 +1781,7 @@ buf_page_init_for_read(
 	buf_LRU_add_block(block, TRUE);		/* TRUE == to old blocks */
 
 	block->io_fix = BUF_IO_READ;
+
 	buf_pool->n_pend_reads++;
 
 	/* We set a pass-type x-lock on the frame because then the same
@@ -1753,6 +1793,7 @@ buf_page_init_for_read(
 
 	rw_lock_x_lock_gen(&(block->lock), BUF_IO_READ);
 
+	mutex_exit(&block->mutex);
 	mutex_exit(&(buf_pool->mutex));
 
 	if (mode == BUF_READ_IBUF_PAGES_ONLY) {
@@ -1817,6 +1858,8 @@ buf_page_create(
 
 	block = free_block;
 
+	mutex_enter(&block->mutex);
+
 	buf_page_init(space, offset, block);
 
 	/* The block must be put to the LRU list */
@@ -1827,13 +1870,15 @@ buf_page_create(
 #else
 	buf_block_buf_fix_inc(block);
 #endif
+	buf_pool->n_pages_created++;
+
+	mutex_exit(&(buf_pool->mutex));
+
 	mtr_memo_push(mtr, block, MTR_MEMO_BUF_FIX);
 
 	block->accessed = TRUE;
 
-	buf_pool->n_pages_created++;
-
-	mutex_exit(&(buf_pool->mutex));
+	mutex_exit(&block->mutex);
 
 	/* Delete possible entries for the page from the insert buffer:
 	such can exist if the page belonged to an index which was dropped */
@@ -1885,6 +1930,12 @@ buf_page_io_complete(
 
 	ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 
+	/* We do not need protect block->io_fix here by block->mutex to read
+	it because this is the only function where we can change the value
+	from BUF_IO_READ or BUF_IO_WRITE to some other value, and our code
+	ensures that this is the only thread that handles the i/o for this
+	block. */
+
 	io_type = block->io_fix;
 
 	if (io_type == BUF_IO_READ) {
@@ -1986,11 +2037,12 @@ buf_page_io_complete(
 		}
 	}
 
+	mutex_enter(&(buf_pool->mutex));
+	mutex_enter(&block->mutex);
+
 #ifdef UNIV_IBUF_DEBUG
 	ut_a(ibuf_count_get(block->space, block->offset) == 0);
 #endif
-	mutex_enter(&(buf_pool->mutex));
-
 	/* Because this thread which does the unlocking is not the same that
 	did the locking, we use a pass value != 0 in unlock, which simply
 	removes the newest lock debug record, without checking the thread
@@ -2033,6 +2085,7 @@ buf_page_io_complete(
 #endif /* UNIV_DEBUG */
 	}
 
+	mutex_exit(&block->mutex);
 	mutex_exit(&(buf_pool->mutex));
 
 #ifdef UNIV_DEBUG
@@ -2095,6 +2148,8 @@ buf_validate(void)
 
 		block = buf_pool_get_nth_block(buf_pool, i);
 
+		mutex_enter(&block->mutex);
+
 		if (block->state == BUF_BLOCK_FILE_PAGE) {
 
 			ut_a(buf_page_hash_get(block->space,
@@ -2139,6 +2194,8 @@ buf_validate(void)
 		} else if (block->state == BUF_BLOCK_NOT_USED) {
 			n_free++;
 		}
+
+		mutex_exit(&block->mutex);
 	}
 
 	if (n_lru + n_free > buf_pool->curr_size) {
@@ -2286,9 +2343,14 @@ buf_get_latched_pages_number(void)
 
 		block = buf_pool_get_nth_block(buf_pool, i);
 
-		if (((block->buf_fix_count != 0) || (block->io_fix != 0))
-		    && block->magic_n == BUF_BLOCK_MAGIC_N) {
-			fixed_pages_number++;
+		if (block->magic_n == BUF_BLOCK_MAGIC_N) {
+			mutex_enter(&block->mutex);
+
+			if (block->buf_fix_count != 0 || block->io_fix != 0) {
+				fixed_pages_number++;
+			}
+
+			mutex_exit(&block->mutex);
 		}
 	}
 
@@ -2458,6 +2520,8 @@ buf_all_freed(void)
 
 		block = buf_pool_get_nth_block(buf_pool, i);
 
+		mutex_enter(&block->mutex);
+
 		if (block->state == BUF_BLOCK_FILE_PAGE) {
 
 			if (!buf_flush_ready_for_replace(block)) {
@@ -2469,6 +2533,8 @@ buf_all_freed(void)
 				ut_error;
 			}
 		}
+
+		mutex_exit(&block->mutex);
 	}
 
 	mutex_exit(&(buf_pool->mutex));

buf/buf0flu.c

@@ -113,6 +113,7 @@ buf_flush_ready_for_replace(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&block->mutex));
 #endif /* UNIV_SYNC_DEBUG */
 	if (block->state != BUF_BLOCK_FILE_PAGE) {
 		ut_print_timestamp(stderr);
@@ -148,6 +149,7 @@ buf_flush_ready_for_flush(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&(block->mutex)));
 #endif /* UNIV_SYNC_DEBUG */
 	ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 
@@ -559,8 +561,15 @@ buf_flush_try_page(
 
 	ut_a(!block || block->state == BUF_BLOCK_FILE_PAGE);
 
+	if (!block) {
+		mutex_exit(&(buf_pool->mutex));
+		return(0);
+	}
+
+	mutex_enter(&block->mutex);
+
 	if (flush_type == BUF_FLUSH_LIST
-	    && block && buf_flush_ready_for_flush(block, flush_type)) {
+	    && buf_flush_ready_for_flush(block, flush_type)) {
 
 		block->io_fix = BUF_IO_WRITE;
 
@@ -598,6 +607,7 @@ buf_flush_try_page(
 			locked = TRUE;
 		}
 
+		mutex_exit(&block->mutex);
 		mutex_exit(&(buf_pool->mutex));
 
 		if (!locked) {
@@ -618,7 +628,7 @@ buf_flush_try_page(
 
 		return(1);
 
-	} else if (flush_type == BUF_FLUSH_LRU && block
+	} else if (flush_type == BUF_FLUSH_LRU
 		   && buf_flush_ready_for_flush(block, flush_type)) {
 
 		/* VERY IMPORTANT:
@@ -659,13 +669,14 @@ buf_flush_try_page(
 		buf_pool mutex: this ensures that the latch is acquired
 		immediately. */
 
+		mutex_exit(&block->mutex);
 		mutex_exit(&(buf_pool->mutex));
 
 		buf_flush_write_block_low(block);
 
 		return(1);
 
-	} else if (flush_type == BUF_FLUSH_SINGLE_PAGE && block
+	} else if (flush_type == BUF_FLUSH_SINGLE_PAGE
 		   && buf_flush_ready_for_flush(block, flush_type)) {
 
 		block->io_fix = BUF_IO_WRITE;
@@ -692,6 +703,7 @@ buf_flush_try_page(
 
 		(buf_pool->n_flush[flush_type])++;
 
+		mutex_exit(&block->mutex);
 		mutex_exit(&(buf_pool->mutex));
 
 		rw_lock_s_lock_gen(&(block->lock), BUF_IO_WRITE);
@@ -709,11 +721,12 @@ buf_flush_try_page(
 		buf_flush_write_block_low(block);
 
 		return(1);
-	} else {
-		mutex_exit(&(buf_pool->mutex));
-
-		return(0);
 	}
+
+	mutex_exit(&block->mutex);
+	mutex_exit(&(buf_pool->mutex));
+
+	return(0);
 }
 
 /***************************************************************
@@ -758,34 +771,48 @@ buf_flush_try_neighbors(
 		block = buf_page_hash_get(space, i);
 		ut_a(!block || block->state == BUF_BLOCK_FILE_PAGE);
 
-		if (block && flush_type == BUF_FLUSH_LRU && i != offset
-		    && !block->old) {
+		if (!block) {
+
+			continue;
+
+		} else if (flush_type == BUF_FLUSH_LRU && i != offset
+			   && !block->old) {
 
 			/* We avoid flushing 'non-old' blocks in an LRU flush,
 			because the flushed blocks are soon freed */
 
 			continue;
-		}
+		} else {
 
-		if (block && buf_flush_ready_for_flush(block, flush_type)
-		    && (i == offset || block->buf_fix_count == 0)) {
-			/* We only try to flush those neighbors != offset
-			where the buf fix count is zero, as we then know that
-			we probably can latch the page without a semaphore
-			wait. Semaphore waits are expensive because we must
-			flush the doublewrite buffer before we start
-			waiting. */
+			mutex_enter(&block->mutex);
 
-			mutex_exit(&(buf_pool->mutex));
+			if (buf_flush_ready_for_flush(block, flush_type)
+			    && (i == offset || block->buf_fix_count == 0)) {
+				/* We only try to flush those
+				neighbors != offset where the buf fix count is
+				zero, as we then know that we probably can
+				latch the page without a semaphore wait.
+				Semaphore waits are expensive because we must
+				flush the doublewrite buffer before we start
+				waiting. */
 
-			/* Note: as we release the buf_pool mutex above, in
-			buf_flush_try_page we cannot be sure the page is still
-			in a flushable state: therefore we check it again
-			inside that function. */
+				mutex_exit(&block->mutex);
 
-			count += buf_flush_try_page(space, i, flush_type);
+				mutex_exit(&(buf_pool->mutex));
 
-			mutex_enter(&(buf_pool->mutex));
+				/* Note: as we release the buf_pool mutex
+				above, in buf_flush_try_page we cannot be sure
+				the page is still in a flushable state:
+				therefore we check it again inside that
+				function. */
+
+				count += buf_flush_try_page(space, i,
+							    flush_type);
+
+				mutex_enter(&(buf_pool->mutex));
+			} else {
+				mutex_exit(&block->mutex);
+			}
 		}
 	}
 
@@ -879,12 +906,15 @@ buf_flush_batch(
 		while ((block != NULL) && !found) {
 			ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 
+			mutex_enter(&block->mutex);
+
 			if (buf_flush_ready_for_flush(block, flush_type)) {
 
 				found = TRUE;
 				space = block->space;
 				offset = block->offset;
 
+				mutex_exit(&block->mutex);
 				mutex_exit(&(buf_pool->mutex));
 
 				old_page_count = page_count;
@@ -901,10 +931,14 @@ buf_flush_batch(
 
 			} else if (flush_type == BUF_FLUSH_LRU) {
 
+				mutex_exit(&block->mutex);
+
 				block = UT_LIST_GET_PREV(LRU, block);
 			} else {
 				ut_ad(flush_type == BUF_FLUSH_LIST);
 
+				mutex_exit(&block->mutex);
+
 				block = UT_LIST_GET_PREV(flush_list, block);
 			}
 		}
@@ -986,10 +1020,14 @@ buf_flush_LRU_recommendation(void)
 		   + BUF_FLUSH_EXTRA_MARGIN)
 	       && (distance < BUF_LRU_FREE_SEARCH_LEN)) {
 
+		mutex_enter(&block->mutex);
+
 		if (buf_flush_ready_for_replace(block)) {
 			n_replaceable++;
 		}
 
+		mutex_exit(&block->mutex);
+
 		distance++;
 
 		block = UT_LIST_GET_PREV(LRU, block);

buf/buf0lru.c

@@ -86,6 +86,9 @@ scan_again:
 	block = UT_LIST_GET_LAST(buf_pool->LRU);
 
 	while (block != NULL) {
+
+		mutex_enter(&block->mutex);
+
 		ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 
 		if (block->space == id
@@ -112,6 +115,8 @@ scan_again:
 			if (block->is_hashed) {
 				page_no = block->offset;
 
+				mutex_exit(&block->mutex);
+
 				mutex_exit(&(buf_pool->mutex));
 
 				/* Note that the following call will acquire
@@ -138,6 +143,7 @@ scan_again:
 			buf_LRU_block_free_hashed_page(block);
 		}
 next_page:
+		mutex_exit(&block->mutex);
 		block = UT_LIST_GET_PREV(LRU, block);
 	}
 
@@ -211,6 +217,9 @@ buf_LRU_search_and_free_block(
 
 	while (block != NULL) {
 		ut_a(block->in_LRU_list);
+
+		mutex_enter(&block->mutex);
+
 		if (buf_flush_ready_for_replace(block)) {
 
 #ifdef UNIV_DEBUG
@@ -226,6 +235,7 @@ buf_LRU_search_and_free_block(
 			buf_LRU_block_remove_hashed_page(block);
 
 			mutex_exit(&(buf_pool->mutex));
+			mutex_exit(&block->mutex);
 
 			/* Remove possible adaptive hash index built on the
 			page; in the case of AWE the block may not have a
@@ -234,15 +244,21 @@ buf_LRU_search_and_free_block(
 			if (block->frame) {
 				btr_search_drop_page_hash_index(block->frame);
 			}
-			mutex_enter(&(buf_pool->mutex));
 
 			ut_a(block->buf_fix_count == 0);
 
+			mutex_enter(&(buf_pool->mutex));
+			mutex_enter(&block->mutex);
+
 			buf_LRU_block_free_hashed_page(block);
 			freed = TRUE;
+			mutex_exit(&block->mutex);
 
 			break;
 		}
+
+		mutex_exit(&block->mutex);
+
 		block = UT_LIST_GET_PREV(LRU, block);
 		distance++;
 
@@ -428,8 +444,12 @@ loop:
 			}
 		}
 
+		mutex_enter(&block->mutex);
+
 		block->state = BUF_BLOCK_READY_FOR_USE;
 
+		mutex_exit(&block->mutex);
+
 		mutex_exit(&(buf_pool->mutex));
 
 		if (started_monitor) {
@@ -838,6 +858,7 @@ buf_LRU_block_free_non_file_page(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&block->mutex));
 #endif /* UNIV_SYNC_DEBUG */
 	ut_ad(block);
 
@@ -877,6 +898,7 @@ buf_LRU_block_remove_hashed_page(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&block->mutex));
 #endif /* UNIV_SYNC_DEBUG */
 	ut_ad(block);
 
@@ -939,6 +961,7 @@ buf_LRU_block_free_hashed_page(
 {
 #ifdef UNIV_SYNC_DEBUG
 	ut_ad(mutex_own(&(buf_pool->mutex)));
+	ut_ad(mutex_own(&block->mutex));
 #endif /* UNIV_SYNC_DEBUG */
 	ut_a(block->state == BUF_BLOCK_REMOVE_HASH);
 

include/buf0buf.h

@@ -461,8 +461,8 @@ Gets the mutex number protecting the page record lock hash chain in the lock
 table. */
 UNIV_INLINE
 mutex_t*
-buf_frame_get_lock_mutex(
-/*=====================*/
+buf_frame_get_mutex(
+/*================*/
 			/* out: mutex */
 	byte*	ptr);	/* in: pointer to within a buffer frame */
 /***********************************************************************
@@ -713,7 +713,10 @@ struct buf_block_struct{
 
 	ulint		magic_n;	/* magic number to check */
 	ulint		state;		/* state of the control block:
-					BUF_BLOCK_NOT_USED, ... */
+					BUF_BLOCK_NOT_USED, ...; changing
+					this is only allowed when a thread
+					has BOTH the buffer pool mutex AND
+					block->mutex locked */
 	byte*		frame;		/* pointer to buffer frame which
 					is of size UNIV_PAGE_SIZE, and
 					aligned to an address divisible by
@@ -731,8 +734,12 @@ struct buf_block_struct{
 	ulint		offset;		/* page number within the space */
 	ulint		lock_hash_val;	/* hashed value of the page address
 					in the record lock hash table */
-	mutex_t*	lock_mutex;	/* mutex protecting the chain in the
-					record lock hash table */
+	mutex_t		mutex;		/* mutex protecting this block:
+					state (also protected by the buffer
+					pool mutex), io_fix, buf_fix_count,
+					and accessed; we introduce this new
+					mutex in InnoDB-5.1 to relieve
+					contention on the buffer pool mutex */
 	rw_lock_t	lock;		/* read-write lock of the buffer
 					frame */
 	buf_block_t*	hash;		/* node used in chaining to the page
@@ -788,20 +795,27 @@ struct buf_block_struct{
 					in heuristic algorithms, because of
 					the possibility of a wrap-around! */
 	ulint		freed_page_clock;/* the value of freed_page_clock
-					buffer pool when this block was
-					last time put to the head of the
-					LRU list */
+					of the buffer pool when this block was
+					the last time put to the head of the
+					LRU list; a thread is allowed to
+					read this for heuristic purposes
+					without holding any mutex or latch */
 	ibool		old;		/* TRUE if the block is in the old
 					blocks in the LRU list */
 	ibool		accessed;	/* TRUE if the page has been accessed
 					while in the buffer pool: read-ahead
 					may read in pages which have not been
-					accessed yet */
+					accessed yet; this is protected by
+					block->mutex; a thread is allowed to
+					read this for heuristic purposes
+					without holding any mutex or latch */
 	ulint		buf_fix_count;	/* count of how manyfold this block
-					is currently bufferfixed */
+					is currently bufferfixed; this is
+					protected by block->mutex */
 	ulint		io_fix;		/* if a read is pending to the frame,
 					io_fix is BUF_IO_READ, in the case
-					of a write BUF_IO_WRITE, otherwise 0 */
+					of a write BUF_IO_WRITE, otherwise 0;
+					this is protected by block->mutex */
 	/* 4. Optimistic search field */
 
 	dulint		modify_clock;	/* this clock is incremented every
@@ -959,7 +973,9 @@ struct buf_pool_struct{
 					number of buffer blocks removed from
 					the end of the LRU list; NOTE that
 					this counter may wrap around at 4
-					billion! */
+					billion! A thread is allowed to
+					read this for heuristic purposes
+					without holding any mutex or latch */
 	ulint		LRU_flush_ended;/* when an LRU flush ends for a page,
 					this is incremented by one; this is
 					set to zero when a buffer block is

include/buf0buf.ic

@@ -337,8 +337,8 @@ Gets the mutex number protecting the page record lock hash chain in the lock
 table. */
 UNIV_INLINE
 mutex_t*
-buf_frame_get_lock_mutex(
-/*=====================*/
+buf_frame_get_mutex(
+/*================*/
 			/* out: mutex */
 	byte*	ptr)	/* in: pointer to within a buffer frame */
 {
@@ -346,7 +346,7 @@ buf_frame_get_lock_mutex(
 
 	block = buf_block_align(ptr);
 
-	return(block->lock_mutex);
+	return(&block->mutex);
 }
 
 /*************************************************************************
@@ -519,6 +519,7 @@ buf_block_buf_fix_inc_debug(
 	ret = rw_lock_s_lock_func_nowait(&(block->debug_latch), file, line);
 
 	ut_ad(ret == TRUE);
+	ut_ad(mutex_own(&block->mutex));
 #endif
 	block->buf_fix_count++;
 }
@@ -531,6 +532,9 @@ buf_block_buf_fix_inc(
 /*==================*/
 	buf_block_t*	block)	/* in: block to bufferfix */
 {
+#ifdef UNIV_SYNC_DEBUG
+	ut_ad(mutex_own(&block->mutex));
+#endif
 	block->buf_fix_count++;
 }
 #endif /* UNIV_SYNC_DEBUG */
@@ -625,23 +629,24 @@ buf_page_release(
 
 	ut_ad(block);
 
-	mutex_enter_fast(&(buf_pool->mutex));
-
 	ut_a(block->state == BUF_BLOCK_FILE_PAGE);
 	ut_a(block->buf_fix_count > 0);
 
 	if (rw_latch == RW_X_LATCH && mtr->modifications) {
-
+		mutex_enter(&buf_pool->mutex);
 		buf_flush_note_modification(block, mtr);
+		mutex_exit(&buf_pool->mutex);
 	}
 
+	mutex_enter(&block->mutex);
+
 #ifdef UNIV_SYNC_DEBUG
 	rw_lock_s_unlock(&(block->debug_latch));
 #endif
 	buf_fix_count = block->buf_fix_count;
 	block->buf_fix_count = buf_fix_count - 1;
 
-	mutex_exit(&(buf_pool->mutex));
+	mutex_exit(&block->mutex);
 
 	if (rw_latch == RW_S_LATCH) {
 		rw_lock_s_unlock(&(block->lock));