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  • What types of locks does MySQL use, like table locks, row locks, and gap locks?
    What types of locks does MySQL use, like table locks, row locks, and gap locks?
    MySQL manages concurrent access using table locks, row locks, and gap locks. Table locks lock the entire table, suitable for scenarios with more reads and fewer writes; row locks allow multiple transactions to operate different rows, improving concurrency; gap locks prevent phantom reading and lock index gaps. These three locks work according to different storage engines and isolation levels.
    Mysql Tutorial . Database 787 2025-06-20 00:55:50
  • How to check the current number of connections and server status?
    How to check the current number of connections and server status?
    To view the current number of connections and server status, you can use the following methods: 1. View the number of server connections: Use ss or netstat commands, such as ss-tuln or netstat-tuln to list the listening ports, and combine ss-tn|wc-l to count the number of TCP connections; 2. Monitor the overall status of the server: use uptime to view the load and runtime, and use top and htop to view the CPU and memory usage in real time; 3. Use monitoring tools to achieve long-term observation: Deploy Grafana Prometheus, Netdata or Zabbix to graphically display data and set alarms; 4. Notes: Handle TIME_WAIT status connection, optimize kernel parameters and query different commands
    Mysql Tutorial . Database 145 2025-06-20 00:55:31
  • What is the functional difference between the WHERE and HAVING clauses?
    What is the functional difference between the WHERE and HAVING clauses?
    In SQL, the main difference between WHERE and HAVING is the execution timing and the type of data filtered. 1.WHERE filters a single row before grouping, and cannot use an aggregation function; 2.HAVING filters the aggregation results after grouping, allowing the use of an aggregation function. For example, when querying departments with more than 10 high-paying employees, WHERE first filters low-paying employees, then uses GROUPBY to group them, and finally uses HAVING to filter groups that meet the criteria. In terms of performance, WHERE should be used to reduce the amount of data, and HAVING should only be used when filtering the aggregate results.
    Mysql Tutorial . Database 854 2025-06-20 00:55:11
  • Which is more efficient: COUNT(*), COUNT(1), or COUNT(column_name)?
    Which is more efficient: COUNT(*), COUNT(1), or COUNT(column_name)?
    InmodernSQLdatabases,COUNT(),COUNT(1),andCOUNT(column_name)havelittletonoperformancedifferenceinbasicqueries.1.COUNT()countsallrows,includingNULLs,andisbestfortotalrowcount.2.COUNT(1)behavesthesameasCOUNT(),withnoperformanceadvantage,andisusedmainlyb
    Mysql Tutorial . Database 274 2025-06-20 00:53:51
  • What are optimistic and pessimistic locks, and how to implement them in MySQL?
    What are optimistic and pessimistic locks, and how to implement them in MySQL?
    Pessimistic locks and optimistic locks are two strategies for handling concurrent database access. Pessimistic locking assumes conflicts and locks are immediately added when the data is modified, such as in MySQL using SELECT...FORUPDATE or SELECT...LOCKINSHAREMODE, which is suitable for high-competitive scenarios but may degrade performance. Optimistic locks assume fewer conflicts and do not lock immediately, but check version numbers or timestamps when updated. They are suitable for low-competitive scenarios and avoid lock overhead, but the application layer needs to handle conflicts. If you choose a pessimistic lock, if you write frequently and have high data consistency requirements; if you choose an optimistic lock, if you have fewer conflicts, you hope to improve concurrency and can handle it elegantly. In addition, pessimistic locks may lead to deadlocks, and optimistic locks require additional logic to handle conflicts.
    Mysql Tutorial . Database 894 2025-06-20 00:51:20
  • What is read-write splitting and how is it implemented?
    What is read-write splitting and how is it implemented?
    Read-writesplittingimprovesdatabaseperformancebyseparatingreadandwriteoperationsacrossdifferentservers.Itworksbydirectingwritestotheprimarydatabaseandreadstoreplicas,reducingload,improvingresponsetime,andenhancingfaulttolerance.Commonimplementationme
    Mysql Tutorial . Database 261 2025-06-20 00:37:31
  • How to design a database sharding strategy?
    How to design a database sharding strategy?
    The core of designing a database sharding strategy is "how to reasonably separate the data without affecting use". The key points include: 1. Select the right shard key, and fields such as user ID that are high-base, evenly distributed and commonly used as query conditions should be selected, such as user ID, to avoid using time or high-frequency query fields to prevent hot spots and cross-slicing problems; 2. Control the number of shards, set to 16 or 32 in the initial stage, and reasonably estimate the total data volume and node bearing capacity to avoid operation and maintenance or expansion problems caused by too much or too little; 3. Optimize query and transactions, reduce cross-slicing queries, use redundancy or intermediate layer aggregation to improve efficiency, pay attention to the limited transaction support in the shard environment, and it is necessary to cooperate with cache or secondary index to optimize query performance, report statistics and other operations, and it is recommended to process in parallel at the application layer to reduce database pressure.
    Mysql Tutorial . Database 639 2025-06-20 00:35:31
  • What is a subquery and does it affect performance?
    What is a subquery and does it affect performance?
    Asubquerycanaffectperformancedependingonitsusage.1.Correlatedsubqueriesmayexecuterepeatedly,onceforeachrowintheouterquery.2.Poorlywrittensubqueriescanpreventefficientindexuse.3.Subqueriesaddcomplexity,makingqueryoptimizationharder.However,moderndatab
    Mysql Tutorial . Database 658 2025-06-20 00:17:40
  • What is a typical process for MySQL master failover?
    What is a typical process for MySQL master failover?
    MySQL main library failover mainly includes four steps. 1. Fault detection: Regularly check the main library process, connection status and simple query to determine whether it is downtime, set up a retry mechanism to avoid misjudgment, and can use tools such as MHA, Orchestrator or Keepalived to assist in detection; 2. Select the new main library: select the most suitable slave library to replace it according to the data synchronization progress (Seconds_Behind_Master), binlog data integrity, network delay and load conditions, and perform data compensation or manual intervention if necessary; 3. Switch topology: Point other slave libraries to the new master library, execute RESETMASTER or enable GTID, update the VIP, DNS or proxy configuration to
    Mysql Tutorial . Database 366 2025-06-19 01:06:41
  • What is MySQL Group Replication (MGR)?
    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
    Mysql Tutorial . Database 227 2025-06-19 01:06:20
  • How to connect to a MySQL database using the command line?
    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
    Mysql Tutorial . Database 952 2025-06-19 01:05:41
  • Why do indexes improve MySQL query speed?
    Why do indexes improve MySQL query speed?
    IndexesinMySQLimprovequeryspeedbyenablingfasterdataretrieval.1.Theyreducedatascanned,allowingMySQLtoquicklylocaterelevantrowsinWHEREorORDERBYclauses,especiallyimportantforlargeorfrequentlyqueriedtables.2.Theyspeedupjoinsandsorting,makingJOINoperation
    Mysql Tutorial . Database 468 2025-06-19 01:05:20
  • What is GTID (Global Transaction Identifier) and what are its advantages?
    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.
    Mysql Tutorial . Database 1108 2025-06-19 01:03:11
  • What is the difference between Percona XtraDB Cluster (PXC) and InnoDB Cluster?
    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:
    Mysql Tutorial . Database 392 2025-06-19 01:01:31

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