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Home

Technical Articles

Database

Mysql Tutorial

What is MySQL Group Replication (MGR)?

MySQLGroupReplication (MGR) is a plug-in high-availability clustering technology officially provided by MySQL, which is based on the Paxos protocol to achieve strong data consistency and automatic failover. 1. MGR synchronizes transaction logs and authenticates them among multiple nodes through the group communication system to ensure data consistency; 2. Its core features include automatic failover, multiple write/single-write mode optional, and built-in conflict detection mechanism; 3. Deployment requires at least three nodes, and configures key parameters such as GTID, row format log, and unique server_id; 4. Common processes include preparing servers, configuring parameters, initializing nodes, joining clusters and status checks. MGR is suitable for scenarios with high data consistency requirements, but is sensitive to network latency

Jun 19, 2025 am 01:06 AM

MGR

How to connect to a MySQL database using the command line?

The steps to connect to the MySQL database are as follows: 1. Use the basic command format mysql-u username-p-h host address to connect, enter the username and password to log in; 2. If you need to directly enter the specified database, you can add the database name after the command, such as mysql-uroot-pmyproject; 3. If the port is not the default 3306, you need to add the -P parameter to specify the port number, such as mysql-uroot-p-h192.168.1.100-P3307; In addition, if you encounter a password error, you can re-enter it. If the connection fails, check the network, firewall or permission settings. If the client is missing, you can install mysql-client on Linux through the package manager. Master these commands

Jun 19, 2025 am 01:05 AM

mysql Command Line

Why do indexes improve MySQL query speed?

IndexesinMySQLimprovequeryspeedbyenablingfasterdataretrieval.1.Theyreducedatascanned,allowingMySQLtoquicklylocaterelevantrowsinWHEREorORDERBYclauses,especiallyimportantforlargeorfrequentlyqueriedtables.2.Theyspeedupjoinsandsorting,makingJOINoperation

Jun 19, 2025 am 01:05 AM

mysql index

What is GTID (Global Transaction Identifier) and what are its advantages?

GTID (Global Transaction Identifier) ??solves the complexity of replication and failover in MySQL databases by assigning a unique identity to each transaction. 1. It simplifies replication management, automatically handles log files and locations, allowing slave servers to request transactions based on the last executed GTID. 2. Ensure consistency across servers, ensure that each transaction is applied only once on each server, and avoid data inconsistency. 3. Improve troubleshooting efficiency. GTID includes server UUID and serial number, which is convenient for tracking transaction flow and accurately locate problems. These three core advantages make MySQL replication more robust and easy to manage, significantly improving system reliability and data integrity.

Jun 19, 2025 am 01:03 AM

gtid Transaction identification

What is the difference between Percona XtraDB Cluster (PXC) and InnoDB Cluster?

PXC and InnoDBCluster are common high-availability clustering solutions in MySQL. The core differences are as follows: 1. Different synchronization mechanisms: PXC uses Galera multi-master replication, supports multi-node writing, and is suitable for high concurrent write scenarios; InnoDBCluster is based on MGR, and the default is single-master mode. Only one node can be written. Although it supports multi-master, the official recommends to use it with caution. 2. Different methods of data consistency guarantee: PXC authenticates before transaction submission to ensure consistency but may increase delays, and rolls back transactions in conflicts; copying after InnoDBCluster after submission, there is a short inconsistency window, and the final consistency is guaranteed through the Paxos protocol, and the network partition tends to maintain availability. 3. The complexity of deployment and operation and maintenance is different:

Jun 19, 2025 am 01:01 AM

How to safely purge old MySQL binlog files?

To clean MySQL binlog files, you should use the PURGEBINARYLOGS command or set the automatic expiration time, and files cannot be deleted directly. 1. Use the PURGE command to clean old logs by file name or time. Before execution, you need to confirm that the slave library no longer uses the relevant logs; 2. Check the current log status and slave library location through SHOWMASTERSTATUS and SHOWSLAVESTATUS to ensure the security of the cleaning range; 3. It is recommended to set the binlog_expire_logs_seconds parameter to achieve automatic cleaning, which is suitable for long-term operation environments; 4. Deleting files directly will cause serious problems such as master-slave synchronization failure and inconsistent log information, and must be avoided.

Jun 19, 2025 am 01:01 AM

mysql binlog

How to choose between DATETIME and TIMESTAMP in MySQL?

When selecting DATETIME and TIMESTAMP types in MySQL, they should be determined based on time zone processing, automatic update, time range, storage space and concurrency requirements. 1. If you need to automatically convert the time zone, you should select TIMESTAMP, which will automatically adjust the display time according to the connection time zone, and DATETIME will always remain the same; 2. If you need to automatically update the fields, TIMESTAMP supports ONUPDATE automatic refresh, and DATETIME only supports the default value; 3. If you need a larger time range (1000 to 9999), select DATETIME, and the TIMESTAMP range is smaller (1970 to 2038); 4. If you are sensitive to storage space, TIMESTAMP accounts for 4.

Jun 19, 2025 am 12:58 AM

datetime

What is the performance impact of using SELECT *?

Using SELECT* will affect database performance and the required columns should be specified explicitly. First, it increases unnecessary data transmission and network load, especially when the table contains a large number of fields (such as TEXT or BLOB); second, it may cause index failure, trigger additional disk I/O operations, and reduce query efficiency; finally, if the table structure changes, SELECT* may cause application errors or unpredictable behavior, reducing maintainability.

Jun 19, 2025 am 12:58 AM

Performance impact SELECT performance

What is the core difference between TRUNCATE TABLE and DELETE FROM TABLE?

The core difference between TRUNCATETABLE and DELETEFROMTABLE lies in the data deletion method and its impact on the database. 1. In terms of log behavior, DELETE records transaction log line by line, supporting rollback and point-in-time recovery, while TRUNCATE only records page release, which is more efficient but has limited functions. 2. In terms of performance, TRUNCATE does not scan progressively, has less competition for locks, and has a small log space, so it is faster and lighter; DELETE is slower due to process progressively. 3. In terms of constraints and dependencies, TRUNCATE cannot be used when there is a foreign key reference (unless cascade truncation is enabled) and does not trigger the trigger; DELETE respects the integrity of the reference and can trigger the trigger. 4. In terms of transaction support, two

Jun 19, 2025 am 12:56 AM

Under what conditions will a MySQL index not be used?

MySQL index may not be used in the following situations: 1. The query conditions do not match the index column or do not start from the leftmost column of the joint index; 2. Perform function or expression operations on the index field; 3. Fuzzy queries starting with % of LIKE; 4. The query conditions do not match the index column data type; 5. The index selectivity is too low, causing the optimizer to give up on use. For example, if the joint index (name,age) is only queried, it will not take effect; using YEAR(create_time)=2023 will cause the index to be invalid; LIKE'?c' cannot go through the index and scan the full table; VARCHAR fields use numerical query to trigger implicit conversion; low-selective fields such as gender fields may be ignored by the optimizer. Mastering these situations helps

Jun 19, 2025 am 12:55 AM

mysql index Unused conditions

What's the difference between caching_sha2_password and mysql_native_password authentication?

caching_sha2_password is more secure and has caching function than mysql_native_password. First, caching_sha2_password uses SHA-256 encryption algorithm to provide stronger security, while mysql_native_password uses the vulnerable SHA-1 algorithm; second, caching_sha2_password supports cache authentication results, improving the performance of frequent connections, while mysql_native_password does not have this function; finally, mysql_native_password has better compatibility and is suitable for old systems, while c

Jun 19, 2025 am 12:52 AM

mysql Certification

What is the process for upgrading MySQL from version 5.7 to 8.0?

UpgradingMySQLfrom5.7to8.0requiresseveralkeysteps:first,checkcompatibilitybyreviewingdeprecatedfeaturesliketheutf8characterset,verifyingpluginsandstorageengines,andensuringapplication-levelcompatibilitywithORMs;second,backupalldatabasesusingmysqldump

Jun 19, 2025 am 12:46 AM

Mysql upgrade 5.7 to 8.0

How to troubleshoot 100% CPU usage by the MySQL server?

Common reasons why MySQL consumes 100% of CPU include slow queries, missing indexes, temporary tables or excessive sorting, and configuration issues. 1. First use SHOWPROCESSLIST to check active connections and resource-consuming operations; 2. Enable and analyze slow query log location historical issues; 3. Check Created_tmp_tables and Sort_merge_passes to judge temporary tables and sorting; 4. Use EXPLAIN to analyze SQL execution plans and optimize full table scanning and file sorting; 5. Check other factors such as connection count, statistical information updates and timing tasks. The above steps can gradually narrow the scope of problems and optimize performance bottlenecks.

Jun 19, 2025 am 12:45 AM

mysql CPU Usage

How to create a new user and grant it only SELECT and INSERT on a specific table?

To create a new user and grant only SELECT and INSERT permissions to a specific table, first create the user using the CREATEUSER statement in MySQL, then authorize it through the GRANT statement, and execute FLUSHPRIVILEGES refresh permissions; in PostgreSQL, also first create the user using CREATEUSER, and then grant the permissions through the GRANTSELECT and INSERTONTABLE statements. 1. Create user: MySQL syntax is CREATEUSER'new_user'@'host'IDENTIFIEDBY'password'; PostgreSQL is CREATEUSE

Jun 19, 2025 am 12:45 AM

mysql User rights