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What are Global Transaction Identifiers (GTIDs) in MySQL replication?

GTIDs are used in MySQL replication to ensure that each transaction is executed uniquely. 1) GTIDs are composed of UUID and incremental transaction IDs, which simplifies data synchronization. 2) To enable GTID replication, you must set gtid_mode and enforce_gtid_consistency to ON on the master server, and use MASTER_AUTO_POSITION=1 on the slave server. 3) GTID supports multi-source replication, but you need to be careful to manage transaction order. 4) Avoid non-transactional statements and GTID conflicts, and when optimizing performance, you can reduce transaction size and use parallel replication.

Apr 06, 2025 am 12:05 AM

gtidMySQL复制

How does indexing work with NULL values in MySQL?

In MySQL, NULL values are not indexed by default, but can be processed through function indexing. 1.NULL values are not usually used by B-Tree index for search. 2. Use function indexes such as IFNULL (discount, 0) to convert NULL values into indexable values. 3. Consider using NOTNULL constraints to simplify index design.

Apr 06, 2025 am 12:04 AM

MySQL索引NULL值

Explain the purpose and usage of the MySQL Performance Schema.

MySQLPerformanceSchema is a tool for monitoring and optimizing database performance. Its functions include identifying performance bottlenecks and optimizing queries. 1) Enable PerformanceSchema to achieve by updating the setup_instruments table. 2) The basic usage includes viewing the current query and waiting for events. 3) Advanced usage involves analyzing the most frequent queries to optimize performance.

Apr 06, 2025 am 12:02 AM

性能监控

What is the Using filesort status in EXPLAIN and how to avoid it?

"Usingfilesort" means that MySQL does not use indexes when sorting, but uses file sorting, which will degrade query performance. Methods to avoid include: 1. Create appropriate indexes, such as CREATEINDEXidx_last_nameONusers(last_name); 2. Adjust the query to use index fields or overwrite the index.

Apr 05, 2025 am 12:05 AM

filesortMySQL优化

What is the InnoDB Adaptive Hash Index?

InnoDBAdaptiveHashIndex accelerates equivalence query by dynamically generating hash indexes. 1) Monitor the query mode, 2) Create hash index, 3) Perform hash search to reduce B-tree traversal and improve query efficiency.

Apr 05, 2025 am 12:03 AM

innodb

Describe strategies for optimizing SELECT COUNT(*) queries on large tables.

Methods to optimize SELECTCOUNT(*) queries include: 1. Use indexes, such as COUNT(1) or COUNT(primary_key); 2. Maintain counter tables and update row counts in real time; 3. Use approximate counting algorithms, such as HyperLogLog, which are suitable for scenarios where accurate counting is not required.

Apr 05, 2025 am 12:02 AM

数据库优化SQL优化

Common causes of replication lag in MySQL and how to troubleshoot.

The reasons for MySQL replication delay include insufficient hardware resources, network problems, large transactions, and lock contention. Solutions include: 1. Monitoring and log analysis, 2. Optimizing hardware resources, 3. Network optimization, 4. Transaction optimization, 5. Lock contention management. Through these measures, replication delays can be effectively reduced, data consistency and system stability can be ensured.

Apr 04, 2025 am 12:13 AM

故障排除

What is Multi-Version Concurrency Control (MVCC) in InnoDB?

MVCC implements non-blocking read operations in InnoDB by saving multiple versions of data to improve concurrency performance. 1) The working principle of MVCC depends on the undolog and readview mechanisms. 2) The basic usage does not require special configuration, InnoDB is enabled by default. 3) Advanced usage can realize the "snapshot reading" function. 4) Common errors such as undolog bloat can be avoided by setting the transaction timeout. 5) Performance optimization includes shortening transaction time, reasonable use of indexes and batch processing of data updates.

Apr 04, 2025 am 12:12 AM

innodbmvcc

Explain Prefix Indexes in MySQL and their trade-offs.

Prefix index is used in MySQL to optimize query for long string columns. 1) Reduce index size and improve query speed. 2) It may lead to a decrease in selectivity and is not applicable to ORDERBY or GROUPBY. 3) Selecting the appropriate prefix length requires testing and adjustment to balance performance and selectivity.

Apr 04, 2025 am 12:10 AM

MySQL索引索引权衡

How does InnoDB perform crash recovery?

InnoDB achieves crash recovery through the following steps: 1. Log playback: read redolog and apply modifications that are not written to the data file to the data page. 2. Roll back uncommitted transactions: Through undolog, roll back all uncommitted transactions to ensure data consistency. 3. Dirty page recovery: handles dirty page writing that is not completed before crash to ensure data integrity.

Apr 04, 2025 am 12:06 AM

What is a covering index in MySQL?

Overriding indexes can significantly improve MySQL query performance. 1) Overwrite index is defined as an index containing all columns required for query, reducing I/O operations. 2) Its working principle uses the B-Tree structure to directly obtain data from the index to avoid returning to tables. 3) Basic usages such as SELECTusername, emailFROMusersWHEREusername='alice', advanced usages can be used for complex query and aggregation operations.

Apr 04, 2025 am 12:03 AM

MySQL索引覆盖索引

How to interpret MySQL EXPLAIN output for query optimization? (key types like ref, range, index, ALL)

MySQL's EXPLAIN command is used to show the query execution plan and help optimize queries. 1) The ref type is used for index search, 2) The range type is used for range query, 3) The index type represents full index scan, 4) The ALL type represents full table scan, which is the slowest.

Apr 03, 2025 am 12:18 AM

MySQL优化

What is index merge optimization in MySQL?

Index merge optimization is a query optimization strategy for MySQL that allows multiple indexes to be used in a single query to speed up data retrieval. Its working principle includes: 1. Index merge intersection, used for AND relationship conditions; 2. Index merge union, used for OR relationship conditions; 3. Index merge sort, used for OR conditions that need to be sorted. This optimization can significantly reduce the number of rows scanned, thereby improving query performance.

Apr 03, 2025 am 12:16 AM

索引优化

How does index cardinality affect query performance in MySQL?

Index cardinality has a significant impact on MySQL query performance. High cardinality indexes can locate data faster and optimize queries; low cardinality indexes may lead to full table scanning. Query performance can be effectively improved by regularly updating statistics, selecting the appropriate index type, avoiding over-index and using over-index.

Apr 03, 2025 am 12:09 AM

MySQL性能索引基数