Mysql method to view and modify time zone

Key points for troubleshooting performance degradation after MySQL upgrade: 1. Check configuration compatibility, parameters may be deprecated or renamed, use mysqld--verbose-help to confirm the supported parameters; 2. Pay attention to the changes in index and execution plan, use EXPLAINANALYZE to compare the execution path, and if necessary, FORCEINDEX and update statistical information; 3. The buffer pool loading method is different, check innodb_buffer_pool_load_at_startup and other parameters, and adjust the loading mode appropriately; 4. Pay attention to default behavior changes such as character sets, isolation levels, etc. It is recommended to read ReleaseNotes before upgrading and go online after verification of the test environment.

TorankrowsordivideresultsetsinMySQL,usewindowfunctionslikeRANK(),DENSE_RANK(),andNTILE().1.RANK()assignsrankswithtiesskippingsubsequentnumbers(e.g.,1,1,3).2.DENSE_RANK()alsohandlestiesbutdoesn’tskipnumbers(e.g.,1,1,2).3.ROW_NUMBER()giveseachrowauniqu

Using precompiled statements can improve security and performance. Its core lies in separating SQL logic from data, preventing SQL injection, and improving efficiency when performing similar queries multiple times. Specific advantages include: 1. By binding the value by placeholder, malicious input is prevented from being interpreted as SQL commands, thereby resisting injection attacks; 2. No need to repeatedly parse SQL when executing queries with the same structure to improve performance; 3. Notes include: performance improvement is limited when only a single query is only, partial driver simulation implementation affects efficiency, difficulty in viewing actual parameter values during debugging, and dynamically building complex queries still require additional processing.

MySQL's REPLACE is a mechanism that combines "delete insert" to replace old data when unique constraint conflicts. When there is a primary key or unique index conflict, REPLACE will first delete the old record and then insert the new record, which is atomic. 1. There must be a primary key or a unique index to trigger the replacement; 2. The old data is deleted during conflict and the new data is inserted; 3. Unlike INSERTIGNORE, the latter ignores conflicts and does not insert them and does not report errors; 4. Pay attention to data loss, self-increasing ID changes, performance overhead and multiple triggering problems of triggers; 5. It is recommended to use INSERT...ONDUPLICATEKEYUPDATE to update some fields instead of full replacement.

To enable MySQL slow query logs, you need to set slow_query_log=1, specify the log path slow_query_log_file, and set the threshold long_query_time. You can optionally record query log_queries_not_using_indexes that do not use the index; pay attention to the Query_time, Rows_examined and Rows_sent indicators when viewing the log; common optimization problems include adding indexes, avoiding index failures caused by functions, adjusting JOIN operations, and using cursor paging instead; excessive logs can be controlled by regular archives, reasonable thresholds, temporary log closing, etc.

The core of MySQL data archiving strategy is to reduce the pressure on the main library while ensuring the queryability and security of historical data. 1. The timing of archiving should be selected when the data is no longer frequently accessed but still needs to be retained, such as orders, logs, and user behavior data exceeding the set period; 2. Archive methods include table partitioning, archive library/table, ARCHIVE engine and external tool pt-archiver, which should be selected according to the access frequency and resource conditions; 3. During the implementation process, attention should be paid to data consistency, index optimization, backup recovery, and permission control; 4. It is recommended to design an automated process to achieve efficient maintenance through timing tasks and monitoring systems.

To optimize MySQL to process high-capacity log data, you should first choose a suitable storage engine such as InnoDB, then optimize the table structure design, then archive old data regularly, and finally adjust the server configuration. Select InnoDB to support transaction and crash recovery, turn off automatic commits for batch inserts, use independent tablespaces, and adjust log refresh policies appropriately. In table design, use TIMESTAMP instead of DATETIME to avoid unnecessary VARCHAR fields and use indexes reasonably. Regularly reduce the amount of data in the main table through partitioning or archives to avoid direct deletion of data. Adjust innodb_log_file_size, max_connections, bulk_insert_buff

In MySQL query optimization, OptimizerHints can be used to intervene when the default query optimizer does not select an ideal execution plan. 1. Control the join order: Adjust the order of multi-table connections through /* NO_JOIN_PREFIX()*/ or /* JOIN_PREFIX()*/, which is suitable for large table connections or inaccurate statistical information; 2. Force the use of specified index: specify specific indexes through /* USE_INDEX()*/ to avoid missed selection of optimizers. Pay attention to the correctness of index names and version compatibility; 3. Control resource usage: For example, set the maximum execution time/* MAX_EXECUTION_TIME()*/ or turn off semi-join optimization