MySQL Pageの読み取りと淘汰プロセスの分析
4980 ワード
Pageディスクの読み取りとロードの反発
buf_page_get_gen
| | ==> rw_lock_s_lock(hash_lock);
| | ==> block = (buf_block_t*) buf_page_hash_get_low(buf_pool, space, offset, fold);
| | ==> if (block == NULL) rw_lock_s_unlock(hash_lock);
| | ==> buf_read_page(space, zip_size, offset) buf_read_page_low
| | ==> bpage = buf_page_init_for_read(err, mode, space, zip_size, unzip, tablespace_version, offset);
| | ==> block = NULL;
| | ==> buf_pool_mutex_enter(buf_pool);
| | ==> rw_lock_x_lock(hash_lock);
| | ==> watch_page = buf_page_hash_get_low(buf_pool, space, offset, fold);
| | ==> if (watch_page && !buf_pool_watch_is_sentinel(buf_pool, watch_page))
| | ==> rw_lock_x_unlock(hash_lock);
| | ==> rw_lock_x_unlock(hash_lock);
| | ==> data = buf_buddy_alloc(buf_pool, zip_size, &lru);
| | ==> buf_buddy_alloc_low(buf_pool, buf_buddy_get_slot(size), lru));
| | ==> block = buf_LRU_get_free_only(buf_pool);
| | ==> rw_lock_x_lock(hash_lock);
| | ==> /* If buf_buddy_alloc() allocated storage from the LRU list, it released and reacquired buf_pool->mutex. Thus, we must check the page_hash again, as it may have been modified. */
| | ==> if (UNIV_UNLIKELY(lru)) {
| | ==> watch_page = buf_page_hash_get_low(buf_pool, space, offset, fold);
| | ==> if (watch_page && !buf_pool_watch_is_sentinel(buf_pool, watch_page)) rw_lock_x_unlock(hash_lock); watch_page = NULL; buf_buddy_free(buf_pool, data, zip_size);
| | ==> HASH_INSERT(buf_page_t, hash, buf_pool->page_hash, fold, bpage);
| | ==> rw_lock_x_unlock(hash_lock);
| | ==> buf_LRU_add_block(bpage, TRUE/* to old blocks */);
| | ==> buf_pool_mutex_exit(buf_pool);
| | ==> buf_block_fix(fix_block);
| | ==> #ifdef PAGE_ATOMIC_REF_COUNT
| | ==> os_atomic_increment_uint32(&block->page.buf_fix_count, 1);
| | ==> #else
| | ==> ib_mutex_t* block_mutex = buf_page_get_mutex(&block->page);
| | ==> mutex_enter(block_mutex);
| | ==> ++block->page.buf_fix_count;
| | ==> mutex_exit(block_mutex);
| | ==> rw_lock_s_unlock(hash_lock);
| | ==> buf_wait_for_read(fix_block);プロセスは次のとおりです.
ステップ3でxロックを解放するのは、スレッドがbpの反発ロックを有し、lrufreelistの操作が反発ロックに依存するためである.従って、bpの反発ロックによって、他のスレッドが空きBlockを申請することをブロックすることができる.しかし、LruからBLockを申請する過程で、スリープ待ちのために反発ロックを解放する必要があり、他のスレッドが入る可能性があるため、第4ステップは、空きBLockのソースに基づいて再チェックが必要かどうかを判断する.
ディスク読み出し中にhashに対する反発コストが比較的高く,xロックが2回加算されていることがわかる.この場所の後続バージョンには最適化があります.
Pageメモリ読み出しとPage淘汰の反発
buf_flush_batch
| | ==> // LRU LOCK
| | ==> buf_pool_mutex_enter(buf_pool);
| | ==> count = buf_do_LRU_batch(buf_pool, min_n);
| | ==> buf_flush_LRU_list_batch(buf_pool, max - count);
| | ==> bpage = UT_LIST_GET_LAST(buf_pool->LRU);
| | ==> mutex_enter(block_mutex);
| | ==> evict = buf_flush_ready_for_replace(bpage);
| | ==> bpage->buf_fix_count == 0
| | ==> mutex_exit(block_mutex);
| | ==> if (evict) buf_LRU_free_page
| | ==> rw_lock_x_lock(hash_lock);
| | ==> mutex_enter(block_mutex);
| | ==> //
| | ==> buf_page_can_relocate
| | ==> // LRU HASH
| | ==> buf_LRU_block_remove_hashed
| | ==> buf_LRU_remove_block(bpage);
| | ==> HASH_DELETE(buf_page_t, hash, buf_pool->page_hash, fold, bpage);
| | ==> rw_lock_x_unlock(hash_lock);
| | ==> buf_pool_mutex_exit(buf_pool);
| | ==> buf_pool_mutex_enter(buf_pool);
| | ==> buf_LRU_block_free_hashed_page((buf_block_t*) bpage);
| | ==> buf_LRU_block_free_non_file_page(block);
| | ==> UT_LIST_ADD_FIRST(list, buf_pool->free, (&block->page));
| | ==> buf_pool_mutex_exit(buf_pool);
Pageの淘汰過程は以下の通りである.