The query cache has been disabled-by-default since My SQL 5.6 (2013) as it is known to not scale with high-throughput workloads on multi-core machines.
Rene confirmed this in his post yesterday, but it has also previously been mentioned by Stewart Smith, Domas Mituzas (update: and Kristian Koehntopp).
Assuming that scalability could be improved, the limiting factor of the query cache is that since only queries that hit the cache will see improvement; it is unlikely to improve We concur with the research performed by Jiamin Huang, Barzan Mozafari, Grant Schoenebeck, Thomas F. We considered what improvements we could make to query cache versus optimizations that we could make which provide improvements to .
While these choices themselves are orthogonal, engineering resources are finite.
My SQL のレプリケーションは、安定稼働やバックアップ、負荷分散などの目的に利用できる優れた機能です。 bin-log (バイナリログ) を利用して Master サーバから Slave サーバに更新を伝播させ、データの複製を行います。Slave サーバでは、2 つのスレッドが動作しています。 IO_THREAD – Master から送られてきたデータを受け取り、relay-log (リレーログ) として書き出す SQL_THREAD – relay-log を読み出し、DB を更新するshow slave status \G *************************** 1.
row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 192.168.12.2 Master_User: replicator Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000024 Read_Master_Log_Pos: 198822658 Relay_Log_File: relay-bin.000048 Relay_Log_Pos: 198730937 Relay_Master_Log_File: mysql-bin.000024 Slave_IO_Running: Yes Slave_SQL_Running: Yes Replicate_Do_DB: Replicate_Ignore_DB: Replicate_Do_Table: Replicate_Ignore_Table: Replicate_Wild_Do_Table: Replicate_Wild_Ignore_Table: Last_Errno: 0 Last_Error: Skip_Counter: 0 Exec_Master_Log_Pos: 1980774 Relay_Log_Space: 1983035 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 265 Master_SSL_Verify_Server_Cert: No Last_IO_Errno: 0 Last_IO_Error: Last_SQL_Errno: 0 Last_SQL_Error: Replicate_Ignore_Server_Ids: Master_Server_Id: 1 Master_UUID: Master_Info_File: SQL_Delay: 0 SQL_Remaining_Delay: NULL Slave_SQL_Running_State: invalidating query cache entries (table) Master_Retry_Count: 86400 Master_Bind: Last_IO_Error_Timestamp: Last_SQL_Error_Timestamp: Master_SSL_Crl: Master_SSL_Crlpath: Retrieved_Gtid_Set: Executed_Gtid_Set: Auto_Position: 0 show master status \G" Warning: Using a password on the command line interface can be insecure.
Scale Arc supports string, boolean, long, double, short, byte, binary, decimal, byte Array, date, time, timestamp, and Character Streams as column types.
For example, consider a product catalog table with a column of “product_id.” The application issues select or update queries to retrieve or update data from the table using “product_id.” Scale Arc uses the “product_id” value as the metadata to tag the cache objects internally.
Scale Arc then has a cache invalidation group consisting of read queries or stored procedures as well invalidation queries or stored procedures all using a common column.The reason for its disabling, is that the query cache does not scale with high-throughput workloads on multi-core machines.This is due to an internal global-lock, which can often be seen as a hotspot in performance_schema.Scale Arc has introduced auto cache invalidation to the industry – a method for automatically invalidating cache entries that enables true ACID-compliant caching.This method tracks data changes by extracting metadata from update or delete queries or from within SQL comments.