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Home

Technical Articles

Database

Mysql Tutorial

How to restore a master from a slave's data?

Recovering the master database usually does not obtain data from the slave database, but when the master database goes down and no backup is available, you can follow the following steps: 1. Check whether the slave database has the latest data, run SHOWSLAVESTATUS\G to confirm that Seconds_Behind_Master is 0 and Last_Error is empty; 2. Stop the copy thread of the slave database and reset the copy information, use the STOPSLAVE and RESETSLAVEALL commands; 3. After configuring the original slave database as a new master database, update the application connection settings and reconfigure the new slave database to point to the master database, use CHANGEMASTERTO to specify the correct binary log file and location; 4. Create a new copy user and grant corresponding permissions; 5. Avoid self-directed

Jun 13, 2025 am 12:22 AM

mysql Data Recovery

How to perform a wildcard search, and what is the difference between % and _?

% matches any number of characters suitable for broad searches, and \_ matches a single character suitable for precise positioning. For example: Li% matches all contents starting with Li, Li\_ only matches three letter names such as Liu or Lia; use LIKE to trigger wildcard characters, which contain special characters and need to be escaped; there are differences in the rules of wildcard characters in different environments.

Jun 13, 2025 am 12:20 AM

sql Wildcard search

What is a Phantom Read and how can it be solved?

Phantom reading refers to the phenomenon of executing the same query twice in a transaction but obtaining different row sets, which are usually caused by inserting or deleting data by another transaction. 1. Use serialized isolation levels to lock the entire data range to prevent phantom reading but may affect performance; 2. Use range locks or key range locks to avoid full table locks and prevent new rows from inserting; 3. Use optimistic concurrency control to detect and deal with phantom reading problems during submission. This problem is particularly important when multiple queries are required to maintain consistency, such as financial reporting, inventory management and other scenarios.

Jun 12, 2025 am 10:40 AM

phantom reading Concurrency control

How to calculate the difference between two dates in days or seconds?

To calculate the number of days or seconds between two dates, the core method is to subtract the time unit into a unified unit. The specific methods include: 1. Use programming languages ??(such as Python's datetime module to create a date object, and then subtract the result through days and total_seconds()); 2. Use subtraction formulas to calculate the difference in the day and multiply by 86400 to obtain the difference in the second; 3. Use online tools or manual conversion to calculate the difference in the day first and then multiply by 86400 seconds per day. Different methods are suitable for different scenarios, logically consistent and simple and easy to implement.

Jun 12, 2025 am 10:38 AM

calculate date difference

How to enable and view the MySQL slow query log?

To enable MySQL slow query logs, you need to modify the configuration file and set relevant parameters. 1. Add slow_query_log=1 to enable logging in the [mysqld] part of my.cnf or my.ini; 2. Set slow_query_log_file to specify the log path, such as /var/log/mysql/mysql-slow.log; 3. Define the slow query threshold through long_query_time, the default unit is seconds. If set to 1, it means to record queries that exceed 1 second; 4. After modification, restart MySQL or use the SETGLOBAL command to take effect dynamically; 5. The log is in text format by default, and you can use tail, cat and other commands to view it.

Jun 12, 2025 am 10:38 AM

Slow query log MySQL slow query

What is the leftmost prefix rule for composite indexes?

Theleftmostprefixruleincompositeindexesmeansqueriesmustreferencetheleftmostcolumnstousetheindexeffectively.Forexample,anindexon(last_name,first_name,email)helpsqueriesfilteringonlast_name,last_nameandfirst_name,orallthreecolumns.However,queriesfilter

Jun 12, 2025 am 10:36 AM

database index

What is the purpose of the InnoDB Buffer Pool?

The function of InnoDBBufferPool is to improve MySQL read and write performance. It reduces disk I/O operations by cacheing frequently accessed data and indexes into memory, thereby speeding up query speed and optimizing write operations; 1. The larger the BufferPool, the more data is cached, and the higher the hit rate, which directly affects database performance; 2. It not only caches data pages, but also caches index structures such as B-tree nodes to speed up searches; 3. Supports cache "dirty pages", delays writing to disk, reduces I/O and improves write performance; 4. It is recommended to set it to 50%~80% of physical memory during configuration to avoid triggering swap; 5. It can be dynamically resized through innodb_buffer_pool_size, without restarting the instance.

Jun 12, 2025 am 10:28 AM

innodb

What is the MySQL binary log (binlog) and what is it used for?

MySQL's binary log (binlog) is a binary log that records database change operations, and is used in scenarios such as data recovery, master-slave replication and auditing. 1. Binlog is a logical log file that records all operation events that modify data, such as INSERT, UPDATE, DELETE, etc., but does not include SELECT or SHOW query statements; 2. Its main uses include: data recovery through replay logs, supporting master-slave copying to achieve data synchronization, and used to analyze operation records to meet audit requirements; 3. Enable binlog requires setting log-bin, server-id, binlog_format and expire_logs_day in the configuration file.

Jun 11, 2025 pm 03:41 PM

mysql binlog

What is the purpose of SELECT ... FOR UPDATE?

ThemainpurposeofSELECT...FORUPDATEistolockselectedrowsduringatransactiontopreventothersessionsfrommodifyingthemuntilthetransactioncompleteswhichensuresdataconsistencyinconcurrentenvironmentssuchasbankingandinventorysystems1Itplacesrow-levellocksallow

Jun 11, 2025 pm 03:37 PM

database Lock

What problems can a long-running transaction cause?

Long transactions can cause multiple problems in the database environment. 1. Locking and blocking: Long transactions hold locks for a long time, preventing other transactions from accessing data, resulting in delay or timeout; 2. Increased risk of deadlock: Cross-waiting of multiple transactions is prone to cause deadlocks, and the database needs to interrupt transaction processing, which may lead to data inconsistency; 3. High resource consumption: Transaction logs and rollback segments occupy more memory and disk space, affecting backup and recovery and system performance; 4. Data consistency and recovery challenges: Uncommitted transactions extend the failure recovery time, and data delay or inconsistency may be caused in the replication environment; therefore transactions should be submitted or rolled back as soon as possible to avoid the above problems.

Jun 11, 2025 pm 03:33 PM

affairs concurrent

How to enable SSL/TLS encryption for MySQL connections?

Enable MySQL's SSL/TLS encryption connection can effectively prevent data leakage. The specific steps are as follows: 1. Confirm that the MySQL version supports SSL, and check whether the return value is YES through SHOWVARIABLESLIKE'have_ssl'; 2. Prepare a PEM format certificate file (ca.pem, server-cert.pem, server-key.pem), which can be generated through OpenSSL or obtained from CA; 3. Modify the MySQL configuration file, add ssl-ca, ssl-cert and ssl-key paths in the [mysqld] section and restart the service; 4. Force the client to use SSL, and use CREATEUSER

Jun 11, 2025 pm 03:29 PM

mysql ssl/tls

How to install MySQL 8.0 on Windows/Linux?

The key to installing MySQL 8.0 is to follow the steps and pay attention to common problems. It is recommended to use the MSI installation package on Windows. The steps include downloading the installation package, running the installer, selecting the installation type, setting the root password, enabling service startup, and paying attention to port conflicts or manually configuring the ZIP version; Linux (such as Ubuntu) is installed through apt, and the steps are to update the source, installing the server, running security scripts, checking service status, and modifying the root authentication method; no matter which platform, you should modify the default password, create ordinary users, set up firewalls, adjust configuration files to optimize character sets and other parameters to ensure security and normal use.

Jun 11, 2025 pm 03:25 PM

database mysql installation

MySQL Triggers: Trigger naming conventions?

MySQLtriggersshouldbenamedusingastructuredconvention:1)Prefixwith'trg_'or'trigger_',2)Includethetablename,3)Specifytheeventtype(insert,update,delete),4)Indicatetiming(beforeorafter);forexample,'trg_tbl_user_before_insert'enhancesreadability,organizat

Jun 06, 2025 am 12:14 AM

MySQL Triggers: Can I disable triggers in some cases?

Yes,youcandisabletriggersinMySQLusingtwomethods.1)Setauser-definedvariabletocontroltriggerexecution:useSET@disable_triggers:=TRUE;beforeoperationsandSET@disable_triggers:=FALSE;tore-enable.2)Renametriggerstemporarily:useRENAMETRIGGERmy_triggerTOmy_tr

Jun 06, 2025 am 12:14 AM