This article experimentally compares the performance of various MySQL COUNT queries on an InnoDB table with one million rows, explains the underlying execution plans using EXPLAIN, analyzes primary‑key versus secondary‑index behavior, and contrasts InnoDB’s fast count implementation.
This article explains how MySQL 8.0.32's InnoDB engine generates, reads, and parses Undo logs for an UPDATE operation, and details the step‑by‑step process of locating the primary record, constructing a rollback record, and restoring both secondary and primary index entries.
This article analyzes why MySQL 8.0.13 introduced the sql_require_primary_key parameter, demonstrates how adding auto‑increment primary keys can cause master‑slave data inconsistencies, explains the underlying InnoDB row‑id behavior, and provides a step‑by‑step solution to synchronize tables.
This article explains MySQL’s internal architecture, covering how data pages, B+‑tree and hash indexes, the Buffer Pool, Adaptive Hash Index, Change Buffer, Undo/Redo logs, the InnoDB storage engine, and the server layer work together to provide fast, reliable CRUD operations and support replication.
This article explains how MySQL 8.0.32 InnoDB generates and stores Update undo logs, detailing the log format, the meaning of each field, how to interpret the log address, and provides concrete SQL examples and shell calculations for practical insight.
This article walks through a real MySQL deadlock case, explaining the background, reproducing the issue, analyzing lock information from InnoDB status, and presenting practical steps to identify root causes and fix the deadlock safely.
This article explains the complete InnoDB undo‑log rollback process on MySQL 8.0, covering preparation, reading and parsing undo logs, constructing primary‑key index records, and the detailed steps for deleting secondary and primary index entries during a transaction rollback.
This article explains MySQL InnoDB's ACID properties in depth, detailing how atomicity relies on Redo and Undo logs, how consistency ensures business logic integrity, how isolation uses locks and MVCC with snapshot and current reads, and how durability is achieved through Redo logs, the innodb_flush_log_at_trx_commit setting, and the Double Write mechanism.
This article investigates a deadlock that occurs when using INSERT … ON DUPLICATE KEY UPDATE in a multi‑threaded MySQL 8.0 environment, reproduces the issue, examines InnoDB lock logs, walks through the relevant source‑code call chain, and demonstrates how gap locks cause the deadlock.
This article explains how MySQL 8.0.32 InnoDB generates and stores Insert Undo logs, detailing their binary format, field meanings, example values, and how the hidden DB_ROLL_PTR field encodes the log address, with accompanying SQL and shell examples.
This article explains how MySQL stores and manages data by introducing the InnoDB storage engine, its buffer pool, data pages, B+Tree and adaptive hash indexes, change buffer, undo/redo logs, binlog, and the server layer that parses, optimizes, and executes SQL statements.
This article explains the internal process MySQL 8.0.32 InnoDB uses to allocate, create, and manage Undo segments—including cached segment retrieval, new segment creation, insertion into rollback segment lists, conflict avoidance through mutexes, and a concise step‑by‑step summary of the entire workflow.
This article explains MySQL InnoDB's multi-version concurrency control (MVCC), covering its basic concepts, hidden columns, isolation levels, the creation and evaluation of Read Views, and includes detailed source code examples and step‑by‑step experiments to illustrate transaction visibility.
This article examines MySQL 8.0.32 InnoDB's rollback segment memory layout and details the algorithms used to allocate rollback segments for user temporary tables and regular tables, including the role of system variables, counters, and the distribution matrix across undo tablespaces.
This article explains why COUNT(*) on a large InnoDB table can take seconds while MyISAM returns instantly, explores the underlying storage‑engine differences, and presents six practical techniques—including Redis counters, counting tables with transactions or triggers, parallel read threads, secondary indexes, and SHOW TABLE STATUS—to dramatically speed up row counting in MySQL.
This article explains the four‑layer logical structure of InnoDB Undo logs—Undo pages, Undo segments, rollback segments, and Undo tablespaces—detailing their roles, management, related system variables, and how they affect transaction rollback and storage in MySQL 8.0.32.
This article provides a concise English recap of the 27 previously published InnoDB lock module articles, covering theoretical concepts such as table and row locks, lock waiting, deadlock handling, and practical scenarios like lock behavior during inserts and duplicate key operations.
This article reviews the long‑standing performance problems of TRUNCATE and DROP TABLE in MySQL, tracing their origins through official manuals and historical bugs, summarizing the optimizations introduced in MySQL 5.5.23, 5.7, 8.0, and 8.4, and offering practical guidance for mitigating remaining latency.
This article examines how InnoDB acquires various row, gap, and next‑key locks during INSERT … ON DUPLICATE KEY UPDATE statements under REPEATABLE‑READ and READ‑COMMITTED isolation levels, illustrating the lock behavior with detailed SQL examples and performance‑schema queries.
This article investigates how many records a plain SELECT * query can return in MySQL 8 by examining max_allowed_packet, packet definitions, single‑row size limits, column count restrictions, InnoDB row formats, and practical experiments that reveal the real constraints on query result size.
This article explains InnoDB lock types, their characteristics, and how MySQL 5.6 and 8.0 handle adding a column without fully locking the table, detailing online DDL, atomic DDL, and performance considerations for large tables.
This article explains MySQL transaction fundamentals, the ACID properties, MVCC implementation, isolation levels, snapshot versus current reads, and the various lock types and modes, and provides practical examples of how different SQL statements acquire locks under InnoDB.
This article examines how InnoDB acquires row‑level locks during INSERT … ON DUPLICATE KEY operations under REPEATABLE‑READ and READ‑COMMITTED isolation levels, explains the lock types on primary and unique indexes, and shows the rollback and lock‑conversion process with concrete SQL examples.
This article examines how MySQL InnoDB decides whether to modify index blocks during UPDATE statements, walks through the internal mysql_update workflow, shows debugging with GDB, explains three test scenarios, and validates the behavior by inspecting block LSNs with the innblock tool.
This article explains why a MySQL 8 InnoDB table with a unique index can still store duplicate rows—especially when indexed columns contain NULL or when logical deletion is used—and presents several practical strategies, including status counters, timestamps, extra IDs, hash fields, and batch‑insert techniques, to enforce true uniqueness.
This article explains how MySQL 8.0.32 InnoDB handles INSERT … ON DUPLICATE KEY UPDATE under REPEATABLE‑READ and READ‑COMMITTED isolation levels, showing the preparation steps, lock acquisition process, and why the same exclusive record lock is obtained in both cases.
This article reproduces a MySQL 8.0.32 InnoDB deadlock using two concurrent DELETE statements on the same secondary index, explains the lock types and lock‑wait graph, and details why the deadlock occurs and how it is resolved.
This article explains how MySQL InnoDB deadlocks occur during order‑record idempotency checks, demonstrates step‑by‑step reproduction with SQL scripts, analyzes the lock types involved, and provides practical strategies to avoid and resolve such deadlocks in production systems.
This article details a MySQL 8.0.35 crash caused by an InnoDB assertion that a VARCHAR length exceeds 65,535 bytes, explains the error‑log and core‑dump analysis, shows how to reproduce the bug, and notes its resolution in MySQL 8.0.35.
This article investigates how many rows should be inserted per batch in MySQL, analyzes the limits of SQL statement size, buffer pool, transaction overhead, and indexes, and presents empirical tests that reveal the most efficient batch size for different data volumes.
This article demonstrates how InnoDB acquires and releases row‑level locks for a sample table under REPEATABLE‑READ and READ‑COMMITTED isolation levels, showing the SQL statements used, the lock types observed in the performance_schema, and the reasons behind the observed locking patterns.
This article demonstrates how InnoDB handles row, next‑key, and gap locks for a SELECT … FOR SHARE query under REPEATABLE‑READ and READ‑COMMITTED isolation levels, showing the preparation steps, SQL examples, lock inspection queries, and a concise summary of the differences.
This article provides a comprehensive overview of MySQL 8.0's concurrency control mechanisms, detailing table‑level MDL locks, server‑ and engine‑layer table locks, page‑level B+Tree locking, and row‑level lock types with code examples and real‑world deadlock scenarios.
This article demonstrates how InnoDB acquires different types of row and gap locks under REPEATABLE-READ and READ-COMMITTED isolation levels by creating a test table, inserting data, setting transaction isolation, executing SELECT ... FOR SHARE statements, and inspecting lock information from performance_schema.
The article demonstrates how MySQL Router 8.2 enables transparent read/write splitting for an InnoDB ReplicaSet, showing the architecture, configuration steps, connection behavior, and the generated routing settings that improve database performance without modifying application code.
The article outlines MySQL’s layered architecture—connector, parser, optimizer, executor, and binary log in the server layer and pluggable storage engines like InnoDB—then walks through the step‑by‑step processing of SELECT and UPDATE statements, highlighting permission checks, caching, plan selection, redo and binlog handling for crash‑safe durability.
This article explains MySQL storage engine concepts, compares InnoDB, MyISAM, and MEMORY, describes how data is stored in shared tablespace versus file‑per‑table modes, and provides configuration commands for switching modes, changing default engines, and inspecting or altering a table’s engine.
This tutorial demonstrates, using MySQL 8.0.32 InnoDB source code, how REPEATABLE-READ and READ-COMMITTED isolation levels affect the locking behavior of SELECT ... FOR SHARE statements on primary‑key rows, including preparation, execution, and detailed lock analysis.
A batch INSERT triggers a massive lock record buildup, and a concurrent SELECT on performance_schema.data_locks causes a memory allocation error that leaves trx_sys‑mutex unreleased, leading to a full MySQL hang; the article reproduces the bug, analyses the stack, explains the root cause, and shows the official fix in MySQL 8.0.37.
This article explains the fundamental concepts of MySQL index structures, detailing how clustered (primary) indexes store data physically in order, how non‑clustered (secondary) indexes reference primary keys, and compares their performance implications and practical usage scenarios.
This article explains how InnoDB’s buffer pool works, covering its purpose, configuration parameters, internal structures such as free, flush, and LRU lists, multi‑instance handling, adaptive hash indexing, and strategies for page eviction and performance optimization.
This article explains the core components of MySQL's InnoDB storage engine—including undo log, redo log, buffer pool, change buffer, and binlog—detailing their roles in data writing, crash recovery, MVCC, and master‑slave synchronization, and describing related flushing strategies and LRU management.
This article investigates whether the REPEATABLE‑READ isolation level in InnoDB fully prevents phantom reads by conducting a series of current‑read and snapshot‑read experiments, analyzing transaction behavior, MVCC mechanisms, and offering recommendations to avoid phantom anomalies.
This article examines how MySQL 8.0.32 InnoDB handles locking when inserting a row that violates a unique index under the READ‑COMMITTED isolation level, detailing the preparation steps, observed lock types, the underlying mechanism, and the final cleanup actions.
This article explains MySQL index classifications, the inner workings of B+‑tree and hash indexes, the differences between clustered and secondary indexes, and advanced concepts such as covering indexes, index push‑down, index merge, cost‑based index selection, and common pitfalls that cause index inefficiency.
This article examines how InnoDB handles row locking when an INSERT triggers a primary‑key index conflict, detailing the lock types on primary and unique indexes, the implicit‑to‑explicit lock conversion, and the role of the supremum record in the locking process.
The article describes a MySQL 8.0.18 backup failure caused by an undo log remaining in cleanup state for over ten hours, details the error logs, shows how the ChatDBA AI tool analyses and resolves the issue, compares it with ChatGPT‑4o, and provides related activity previews.
MySQL 8.4 becomes the new LTS release, offering detailed upgrade‑downgrade compatibility tables, dozens of InnoDB and temporary‑table parameter defaults, MGR and replication enhancements, new commands, and a list of deprecated features to help DBAs plan migrations efficiently.
This article walks through a real‑world MySQL InnoDB deadlock case, detailing log analysis, reproducing the issue with test data, explaining gap and insert‑intention locks, and presenting a practical solution that checks existence before updating or inserting to prevent deadlocks.
This article explains the mechanisms behind MySQL auto‑increment primary keys, why gaps appear after failed inserts, unique‑index violations, transaction rollbacks, and batch operations, and how storage engines and innodb_autoinc_lock_mode settings influence the continuity of generated IDs.
This article explains why MySQL auto‑increment primary keys can become non‑continuous, covering storage mechanisms, unique‑index violations, transaction rollbacks, batch inserts, and step‑size settings, and provides practical examples and diagrams to help developers diagnose and avoid ID gaps.
This article examines how InnoDB acquires shared record locks during a duplicate‑primary‑key INSERT, explains the underlying lock‑checking mechanism, demonstrates lock behavior with concurrent DELETE and INSERT transactions, and provides SQL examples and performance_schema queries to illustrate the process.
This article examines whether the REPEATABLE‑READ isolation level in InnoDB fully prevents phantom reads by conducting systematic current‑read and snapshot‑read experiments, analyzing lock mechanisms, MVCC behavior, and presenting detailed SQL scripts, results, and recommendations for avoiding phantom reads.
This article explains what implicit locks are in MySQL InnoDB, how to identify their presence on primary and secondary index records, the conditions under which they appear, and the process by which they are converted into explicit locks that can be inspected via performance_schema.
This article presents a detailed walkthrough of a MySQL InnoDB deadlock case, covering background, log inspection, data preparation, reproduction steps, lock analysis, root‑cause explanation, and practical solutions to prevent and resolve similar deadlock issues.
This article explains the purpose, evolution, configuration parameters, and step‑by‑step maintenance procedures for MySQL Undo tablespaces, covering versions from pre‑5.6 to 8.0 and providing practical commands for viewing, creating, truncating, and dropping Undo tablespaces.
This article provides a step‑by‑step analysis of MySQL 8.0.32 InnoDB deadlock logs, covering preparation, log extraction, auxiliary information, transaction details, row‑lock structures, and the final summary, with full SQL examples and code snippets for deep understanding.
This article explains how InnoDB in MySQL 8.0.32 grants table and row locks, detailing the active versus passive acquisition, the lock‑granting algorithms for tables and rows, and the priority, weight, and FIFO rules that determine lock ordering and deadlock handling.
This article explains MySQL InnoDB’s linear and random prefetch mechanisms, the role of the innodb_read_ahead_threshold and innodb_random_read_ahead variables, and how the LRU buffer‑pool list manages hot and cold pages to improve overall query efficiency.
This article explains the MySQL 8.0 Clone plugin introduced in version 8.0.17, compares it with Xtrabackup, details its five‑step cloning process, describes the code structure across SQL, plugin, and InnoDB layers, and outlines the page‑archiving subsystem used to track dirty pages during cloning.
The article explains how MySQL Router 8.2 automatically splits read and write traffic in an InnoDB ReplicaSet, routing reads to asynchronous replicas and writes to the primary, providing performance, scalability, and simplified management without any application‑level changes.
This article explains how MySQL's Buffer Pool caches data in memory, its default size and configuration, the internal structure of instances, chunks, control blocks and pages, and how it manages data loading, dirty pages, and flushing to disk for optimal query performance.
A mock interview walks through MySQL transaction fundamentals, ACID principles, MVCC mechanics, undo log structures, and the differences between Read Committed and Repeatable Read isolation levels, illustrating each concept with code snippets and diagrams.
While MySQL 5.7 native DDL methods (copy, inplace rebuild, index build, metadata‑only) vary in speed, space use, lock impact, and binlog output, GH‑OST consistently offers the fastest execution, lowest lock blocking, real‑time replication, albeit at roughly double storage cost, making it ideal for risk‑averse online schema changes.
This article explains the various moments when InnoDB table and row locks are released during a transaction's lifecycle, covering mismatched WHERE conditions, the two‑phase commit prepare stage, AUTO‑INC locks, and differences across isolation levels in MySQL 8.0.32.
This article explains the limitations of MySQL's built‑in query cache, how the InnoDB buffer pool works and can be tuned, and introduces ReadySet as an external caching middleware to improve query performance after a major product upgrade.
MySQL’s pluggable storage‑engine architecture lets each table use a specific engine, with InnoDB (the default in MySQL 8.x) offering row‑level locking, ACID transactions, foreign‑key support, crash recovery, MVCC and a buffer pool, while MyISAM provides only table‑level locking, no transactions, and is suited mainly for read‑intensive workloads lacking recovery requirements.
This article explains how InnoDB resolves a deadlock by ordering the involved transactions, selecting a victim based on priority, rollback cost and table modifications, updating transaction weights, optionally logging the deadlock details, and finally waking the victim transaction to roll back.
This article explains how MySQL's InnoDB deadlock detection thread works, when it checks for deadlocks based on the innodb_deadlock_detect variable, how it discovers lock‑wait cycles, performs a secondary verification using snapshot and slot information, and finally summarizes the overall process.
This article demonstrates how MySQL Router 8.2 can perform automatic read/write splitting using an InnoDB ReplicaSet, shows the required configuration, explains the behavior of read and write connections, and concludes with the benefits of the feature while also containing promotional material for unrelated services.
This article explains how InnoDB simulates deadlocks, how the ib_srv_lock_to background thread checks for deadlocks, how it builds lock‑wait snapshots, constructs lock‑wait graphs, calculates transaction weights, and finally resolves deadlocks, illustrated with detailed SQL examples and code snippets.
Upgrading to MySQL 8.0.38 (or later) causes crashes when an instance contains more than ten thousand tables, even with validate_tablespace_paths disabled, but using a shared or general tablespace configuration can reliably avoid the failure.
This article analyzes why two identical DELETE statements on a MySQL table with a unique index can deadlock, explains InnoDB lock types, walks through the execution flow, reproduces the issue with SQL and Java code, and discusses mitigation strategies.
This article explains the inner workings of InnoDB’s lock‑wait timeout thread, detailing how it scans waiting slots, identifies timed‑out transactions, processes timeout logic, and notifies the affected transactions, while also covering related data structures and configuration variables.
This article explains how MySQL Router 8.2 enables read/write splitting for an InnoDB ReplicaSet, showing configuration steps, routing behavior, sample code, and the resulting performance and management benefits without requiring application changes.
This article explains how two identical DELETE statements on a table with a unique index can cause a deadlock in MySQL 5.7, reviews InnoDB lock types, reproduces the issue with SQL and Java code, and discusses mitigation strategies and behavior changes in MySQL 8.
This article examines why identical DELETE statements on a MySQL table with a unique index can cause deadlocks, reviews InnoDB lock types, reproduces the issue with SQL and Java code, and discusses mitigation strategies such as version upgrades, isolation level changes, and distributed locks.
This article explains how InnoDB handles lock waiting by allocating lock structures, registering waiting slots, recording start times, and notifying transactions, outlining each step of the queue‑registration‑notification workflow in MySQL 8.0.32.
This article investigates whether MySQL re‑executes an UPDATE statement that sets a column to its current value, comparing behavior under binlog_format=ROW and binlog_format=STATEMENT with binlog_row_image=FULL, and presents test steps, results, and conclusions.
This article explains the slow‑path row‑locking algorithm used by InnoDB in MySQL 8.0.32, detailing how the engine checks whether a transaction already holds a lock, determines if it must wait, reuses existing lock structures, and allocates new ones when necessary.
This article explains how InnoDB implements row locking by dividing the process into fast and slow paths, describing the hash‑based lock table, token acquisition, lock‑structure creation, bitmap handling, and the conditions that trigger slow‑lock logic.
This article examines the practical limits of MySQL single‑table row counts, explains how InnoDB stores data in 16 KB pages, analyzes B+‑tree index structures, and provides formulas and experiments that justify the commonly cited 20 million‑row guideline.
This article explains the types of InnoDB row‑level locks—record lock, gap lock, and next‑key lock—describes how MySQL determines lock ranges based on indexing, outlines the two fundamental locking principles with associated optimizations, and provides concrete examples for primary‑key and ordinary indexes.
This article explains InnoDB lock concepts, differentiates read and write locks, discusses table‑level versus row‑level locking, and examines how MySQL 5.6 and 8.0 handle adding columns without fully locking tables, highlighting online DDL, atomic DDL, and performance considerations.
This article explains how InnoDB determines whether a transaction already holds a table lock, acquires a mutex token, checks for blocking locks, and creates or reuses lock structures, detailing the complete table‑lock acquisition workflow in MySQL 8.0.32.
This article explains the structure and components of InnoDB's lock module, including the global lock_sys object, its hash tables, latch mechanisms, waiting thread slots, and related attributes, with detailed code examples and diagrams to illustrate how row and table locks are managed.
This article examines the shared and distinct fields of InnoDB's table‑lock and row‑lock structures in MySQL 8.0.32, explains the layout of the lock_t, lock_table_t and lock_rec_t structs, decodes the type_mode bit‑field, and discusses how InnoDB merges compatible row‑locks using a bitmap memory area.
This article explains the different types of InnoDB row locks—including shared, exclusive, gap, next‑key, and insert‑intention locks—by showing preparation steps, SQL examples, lock‑mode details, and how they interact under repeatable‑read isolation in MySQL 8.0.32.
This article presents a MySQL "table is full" error case, explains how the AI‑powered assistant ChatDBA analyzes possible causes such as insufficient temporary tablespace, heavy temporary table creation, and disk limits, and provides step‑by‑step configuration adjustments to resolve the issue.
This article explains the architecture of MySQL's InnoDB storage engine locks, covering server‑level metadata locks, table‑level shared and exclusive locks, intent locks, and the three modes of AUTO‑INC locks, with practical SQL examples and performance‑schema queries.
This article explains MySQL's transaction concepts, the four isolation levels defined by the SQL standard, how each level prevents dirty reads, non‑repeatable reads, and phantom reads, and provides practical commands and example experiments to configure and observe their behavior in InnoDB.
This article provides a comprehensive overview of InnoDB's transaction lock subsystem in MySQL, explaining row‑level and table‑level lock types, their internal implementations, lock‑compatibility rules, practical SQL examples, and common deadlock scenarios with detailed code illustrations.
This article explains MySQL InnoDB’s write‑ahead logging, detailing the roles of Buffer Pool, Redo and Undo logs, checkpoint mechanisms, and how they ensure data consistency and atomicity when a sudden power loss occurs.
The article explains the release of MySQL 8.4 as the first LTS version, compares LTS and Innovation release tracks, and details the 20 InnoDB system variables whose default values have been changed to better suit modern production environments, including performance‑related settings and hardware‑aware defaults.
This article summarizes the major changes introduced in MySQL 8.4, including updated InnoDB parameters, revised default values, new cloning plugin rules, Windows SASL‑based LDAP authentication, and adjustments to replication settings, helping developers and DBAs optimize their database configurations.
This article explains where MySQL stores auto‑increment values, why gaps appear after failed inserts, duplicate‑key errors, rollbacks or batch inserts, and how different innodb_autoinc_lock_mode settings and MySQL 8.0 improvements can mitigate the issue.
This article reviews the 14-part series on MySQL's transaction module, covering initialization, transaction types, two‑phase commit, binlog handling, savepoints, and full rollback, and provides links to each detailed post, including discussions on BEGIN statements, read‑only transactions, and the internal mechanisms of InnoDB.
This article explains how MySQL 8.0.32 rolls back a transaction by first attempting a binlog rollback (which does nothing for a plain ROLLBACK), then performing InnoDB undo‑log processing, committing the internal InnoDB changes, and finally clearing temporary binlog data from the transaction cache.
This article explains the default repeatable‑read isolation level in InnoDB, details the three main lock types—record, gap, and next‑key—and shows how SELECT … FOR UPDATE applies different locking rules depending on primary key, unique, ordinary, range, or table‑scan queries, with practical SQL examples.
This article explains how MySQL 8.0.32 InnoDB rolls back to a specific savepoint by locating the savepoint in the thread's m_savepoints list, discarding relevant binlog entries, applying undo logs in reverse order, and finally removing any later savepoints, with full code examples.
