This guide explains how to restore MySQL databases when the server cannot start by generating table definitions with mysqlfrm, discarding damaged InnoDB tablespaces, copying old .ibd files, and importing them back, followed by verification using mysqlcheck.
The article evaluates MySQL 8.0.21's new ability to disable the InnoDB redo log, comparing load‑data performance with redo log enabled and disabled, and discusses practical implications, limitations, and safety considerations for bulk data import scenarios.
This article explains the differences between normal and unique indexes in MySQL, examines how they affect query and update performance, details InnoDB's change‑buffer mechanism, and provides practical guidance on when to prefer ordinary indexes for better write efficiency.
This article explains InnoDB's 16KB page structure, row formats, record metadata, primary key strategies, and how B+Tree indexes—including clustered, secondary, and covering indexes—organize and retrieve data, with practical SQL examples and performance considerations.
This article explains MySQL's two‑layer architecture, the step‑by‑step execution flow of an SQL statement—including connection, query cache, parser, optimizer, executor, and storage engine—and the roles of redo log and binlog in ensuring data consistency.
This article explains the three most important MySQL log types—redo log, undo log, and binary log—detailing their purposes, contents, creation and release timing, related configuration parameters, physical files, and how they interact with transaction processing and replication.
After upgrading a MySQL 5.6 master to 5.7, inserts on several InnoDB tables began failing with duplicate‑key errors because the auto_increment value became inconsistent, and the article walks through kernel‑level investigation, reproduction steps, bug analysis, and practical fixes.
This article explains MySQL transaction isolation concepts, the four standard isolation levels, their effects on dirty, non‑repeatable, and phantom reads, practical configuration steps, when to use repeatable read, how InnoDB implements isolation, and tips for avoiding long transactions and planning backups.
MySQL 8.0.21 introduces numerous enhancements such as dynamic redo log control, optional tablespace path validation, refined lock system, JSON_VALUE function, atomic CREATE TABLE…AS SELECT, optimizer improvements, reduced group replication cache, multi‑address X Plugin support, and various security and deprecation updates.
The article explains why adding @Transactional in Spring may fail to roll back when MySQL uses the MyISAM engine, shows the required Hibernate dialect configuration for InnoDB, and offers tips for diagnosing similar transaction issues.
This article tests whether MySQL re‑executes an UPDATE statement that does not change any column values, comparing the behavior under binlog_format=ROW and binlog_format=STATEMENT on MySQL 5.7.25 running on CentOS 7.4.
After upgrading a critical MySQL client from 5.6 to 5.7, duplicate‑key errors appeared during inserts on master, replica and read‑only instances, prompting a deep dive into InnoDB auto‑increment mechanics, related kernel bugs, on‑site analysis, and both application‑side and engine‑side remediation strategies.
After upgrading a critical MySQL 5.6 database to 5.7, inserts on the master began failing with duplicate‑key errors due to unexpected auto‑increment values, prompting a deep dive into InnoDB internals, related bugs, and practical mitigation steps.
This article explains how MySQL 8.0 introduces atomic DDL by moving the data dictionary into InnoDB system tables, describes the pre‑8.0 non‑atomic behavior, outlines the DDL execution phases, shows practical comparison results, and details how to view and configure DDL logs.
This article walks through the evolution of MySQL index implementations—from hash tables and binary search trees to AVL, red‑black, B‑trees and finally B+ trees—explaining their performance trade‑offs, disk‑I/O considerations, and how InnoDB and MyISAM store data and indexes differently.
The article explains why a SELECT COUNT(*) on a 5‑million‑row InnoDB table was extremely slow, analyzes the execution plan, demonstrates that the query used the primary (clustered) index, and shows how creating a small secondary index reduces the runtime from dozens of seconds to under a second.
The article explains why MySQL may fail to start when the number of required AIO event slots exceeds the system's fs.aio-max-nr setting, demonstrates how to observe the slots with strace, and provides formulas and recommendations for configuring fs.aio-max-nr in single‑ and multi‑instance deployments.
This article explains MySQL's locking mechanisms, detailing row‑level, table‑level, and page‑level locks, their characteristics and usage, and compares optimistic and pessimistic concurrency control, including implementation methods, storage‑engine specifics, deadlock causes, and strategies to avoid them.
This article provides a comprehensive, step‑by‑step guide to MySQL's locking mechanisms—including table, row, gap, and deadlock handling—covering both MyISAM and InnoDB engines, complete with SQL examples, visual demonstrations, and practical tips for high‑concurrency scenarios.
This article provides a detailed overview of MySQL's locking mechanisms—including table, row, gap, and deadlock handling—across MyISAM and InnoDB storage engines, with practical code examples, performance considerations, and solutions for high‑concurrency scenarios.
This article explains the concept of half‑consistent reads in MySQL InnoDB, describes the conditions under which they occur, presents two test cases with detailed lock‑waiting behavior, analyzes why certain sessions are blocked or not, and summarizes the optimization benefits for RC isolation level.
This article explains the storage units of InnoDB, how B+‑tree indexes are organized on pages, calculates the maximum number of rows a B+ tree can hold based on page size and pointer count, and shows how to determine the tree height from the tablespace file.
This article experimentally investigates whether MySQL re‑executes UPDATE statements that set a column to its current value, comparing behavior under ROW and STATEMENT binlog formats and revealing how InnoDB handles redundant updates.
This article investigates how MySQL handles UPDATE statements that set columns to their existing values, comparing the behavior under ROW and STATEMENT binlog formats with binlog_row_image set to FULL, and shows that duplicate updates are skipped in ROW mode but executed in STATEMENT mode.
This article explains how to retrieve and interpret key MySQL performance metrics—including TPS, QPS, thread status, InnoDB I/O, buffer pool health, MyISAM statistics, temporary tables, response time, and replication lag—using mysqladmin, SHOW GLOBAL STATUS, and Percona tools, with practical calculation formulas and command examples.
This article presents a hands‑on experiment that measures the performance impact of using pt‑table‑checksum on a MySQL master‑slave setup, explains the tool’s design choices such as reduced lock‑wait time and RR isolation, and concludes that its effect on production traffic is minimal when configured properly.
This article analyzes a production incident where concurrent MySQL transactions caused an over‑deduction of account balance, explains the underlying MVCC mechanism, consistency view rules, and how different isolation levels (RR vs RC) affect data visibility and lead to negative balances.
This article analyzes a real‑world MySQL incident where concurrent transactions caused an account balance to become negative, explains the underlying MVCC mechanism, consistency view rules, and how different isolation levels (RR vs RC) affect data visibility and locking behavior.
This article explains the internal B+Tree layout of InnoDB indexes, detailing page types, record organization, and how different primary‑key data types affect page density and overall index tree height, illustrated with concrete examples and visual diagrams.
The article explains why MySQL's AUTO_INCREMENT primary keys can become non‑monotonic and non‑continuous due to early‑version in‑memory counters, restart behavior, concurrency lock modes, and how MySQL 8.0 persists the counter to mitigate these issues while discussing design trade‑offs and best practices.
The article examines why MySQL queries become slow, detailing system‑level issues such as network latency, I/O bottlenecks, and CPU settings, alongside database‑level problems like missing indexes, type conversion, poor execution plans, lock contention, skewed data, and inefficient SQL patterns, and offers optimization strategies.
MySQL 8.0.20 introduces a range of enhancements including new SHOW_ROUTINE privilege, hash join improvements, index‑level optimizer hints, performance schema refinements, SQL syntax changes, InnoDB doublewrite buffer relocation, binary log transaction compression, X Plugin and protocol upgrades, and additional replication options.
This article explains the differences between MySQL table locks and row locks, how they are implemented by the server and storage engines, the lock modes and types (including intention, auto‑increment, gap, next‑key, and insert‑intention locks), and provides practical SQL examples with diagrams.
This article provides a comprehensive overview of MySQL InnoDB locking, covering shared/exclusive locks, intention locks, record locks, gap locks, next‑key locks, insert‑intention locks, and auto‑increment locks, with examples, compatibility tables, and practical SQL snippets to illustrate each mechanism.
This article explains the causes of MySQL InnoDB row lock wait timeout errors, distinguishes row and metadata lock waits, and provides practical methods—including manual replication, monitoring scripts, general_log analysis, and Performance Schema queries—to locate, diagnose, and resolve such locking issues.
This article explains the concept of MySQL Undo Log, traces its evolution from version 5.5 to 8.0, and provides step‑by‑step instructions with examples for creating, viewing, configuring, deleting, and moving undo tablespaces, highlighting the new parameters and defaults introduced in MySQL 8.0.
This article explains InnoDB's logical storage hierarchy of tablespaces, segments, extents, and pages, then details MySQL's partitioning concepts, types, creation syntax, and performance considerations, providing practical examples and guidance for effective database design.
This article explains the complete disk‑write journey of a MySQL INSERT statement, detailing the roles and order of redo log, binlog, double‑write, insert buffer, and data files, and clarifying InnoDB’s buffer‑pool and flushing mechanisms.
This article explains how InnoDB organizes data with B+ trees, calculates the maximum number of rows a single tree can hold (around 20 million), and shows how page size, pointer count, and tree height affect MySQL index performance.
This article explains why MySQL requires locking, compares table and row lock types, details MyISAM and InnoDB lock mechanisms—including optimistic vs. pessimistic locks, lock algorithms, and deadlock handling—while providing practical SQL examples and prevention strategies.
This article explains the principles of pessimistic concurrency control in relational databases, details the conditions under which MySQL's SELECT … FOR UPDATE works, compares it with optimistic locking, provides concrete SQL examples, and demonstrates lock behavior through multiple transaction test scenarios.
This article explains how MySQL computes replication delay using show_slave_status, analyzes the relationship between binlog write timestamps and event generation, enumerates common causes of lag, and provides a detailed examination of the system‑lock state in the slave SQL thread with code examples.
This article explains InnoDB's logical storage hierarchy—tablespace, segment, extent, page—then details MySQL partitioning concepts, types, example DDL, performance impacts, and best‑practice tips for OLTP and OLAP workloads.
The article examines why a 100 GB MySQL 5.6 transaction causes high CPU usage during lock_number_of_rows_locked calculation, compares the lock‑counting implementations of MySQL 5.6 and 5.7, and offers diagnostic steps and version‑upgrade recommendations to mitigate the bottleneck.
This article analyzes a MySQL InnoDB deadlock caused by concurrent batch inserts into a table with a composite unique index, explains the lock types involved, and offers practical strategies such as shortening transactions and lowering isolation levels to avoid similar deadlocks.
This article explains the differences between MySQL table locks and row locks, describes how MyISAM and InnoDB handle locking, provides explicit lock syntax with examples, discusses gap locks, and offers practical recommendations for avoiding lock contention in concurrent applications.
This article explains what MySQL indexes are, the different categories such as ordinary, unique, composite, clustered and non‑clustered, how B‑Tree, B+Tree and hash indexes are implemented in InnoDB and MyISAM, and why auto‑increment primary keys are recommended for optimal performance.
This tutorial explains MySQL fundamentals, the advantages of using MySQL, detailed concepts of indexes, how they work, step‑by‑step SQL examples for creating, viewing, and dropping indexes, best‑practice principles, and query‑optimization techniques to improve performance.
This article provides a comprehensive overview of MySQL InnoDB's internal architecture, covering its memory and disk structures, buffer pool, change buffer, adaptive hash index, log buffer, various tablespace types, page layout, undo and redo logs, double‑write buffer, transaction isolation levels, and how the engine satisfies ACID properties.
This tutorial explains how to create and operate a MySQL InnoDB ReplicaSet—deploying sandbox instances, configuring a replica set with primary and secondary roles, adding nodes, performing manual primary switches and failure recovery, and using MySQL Router to provide an automatic read/write endpoint, while highlighting current limitations.
This article explains the MySQL COUNT function, compares COUNT(*), COUNT(1) and COUNT(column) usages, discusses common interview questions, and details the specific optimizations MyISAM and InnoDB apply to COUNT(*) queries, concluding with best‑practice recommendations.
This article explains MySQL's row size restrictions at both the Server and InnoDB layers, detailing the calculation methods, relevant source code paths, error messages, and practical guidelines for ensuring total record length stays within the 65535‑byte server limit and the 8126‑byte InnoDB limit.
This article explains MySQL's row size restrictions, the differences between server and InnoDB limits, how VARCHAR and TEXT columns affect those limits, and demonstrates through calculations and tests the maximum count of TEXT fields that can be stored under various strict‑mode settings.
This article explains the fundamentals of MySQL InnoDB transaction isolation levels, describes the four standard isolation grades, shows how InnoDB implements them in source code, and provides concrete case studies with SQL scripts to illustrate locking behavior and MVCC effects.
This article explains how MySQL's InnoDB engine applies locks for DELETE and SELECT statements, covering MVCC, snapshot and current reads, clustered indexes, left‑most prefix rules, two‑phase locking, isolation levels, gap and next‑key locks, and analyzes nine different index‑and‑isolation scenarios with detailed conclusions.
This article explains how MySQL's Adaptive Hash Index (AHI) works, why it is needed to reduce B‑tree lookup costs, the three stages of building an AHI, practical examples of its construction, performance benefits, and operational recommendations for managing AHI in production environments.
This article explains the internal structure of InnoDB rollback segments, UNDO log storage formats, and the recovery process in MySQL, detailing how transaction IDs, segment headers, page headers, and log records are organized and used to safely roll back or purge data.
This article explains the InnoDB logical storage architecture—including segments, extents, and pages—then introduces MySQL table partitioning concepts, details the main partition types (RANGE, LIST, HASH, KEY) with SQL examples, and discusses their performance implications for OLTP and OLAP workloads.
This article explains how InnoDB uses REDO logs to recover a crashed MySQL database, detailing the steps of locating checkpoints, scanning log segments, parsing mini‑transactions, storing records in hash tables, and applying them to restore data consistency.
This article explains the essential role of MySQL REDO logs in ensuring data durability and performance, describes what would happen without logging, details various REDO log record formats, and outlines the multiple moments when InnoDB flushes logs to disk.
This article explains the purpose and management of InnoDB REDO log files, the role of Log Sequence Numbers, the structure of log pages, the MTR physical transaction mechanism, and how checkpoints ensure data integrity in MySQL databases.
This article explains the theory behind InnoDB's log management, details the architecture and dynamic sizing of the Buffer Pool, describes its internal data structures and multi‑instance implementation, and provides annotated source code snippets to illustrate how MySQL allocates and manages buffer pages.
The article explains MySQL InnoDB’s four transaction isolation levels, how the default Repeatable Read is realized through MVCC versioning and snapshot reads, and details the three lock types—record, gap, and next‑key—illustrating their roles in preventing dirty, non‑repeatable, and phantom reads.
MySQL 8.0.19 introduces InnoDB ReplicaSet, Router enhancements, numerous SQL syntax additions, optimizer improvements, new Information Schema role views, security features, replication options, X Protocol compression, and a range of deprecations and bug fixes, providing a comprehensive update for database administrators and developers.
This article explains how MySQL executes COUNT(*) and COUNT(column) queries on InnoDB tables, showing example results, detailing each layer's processing steps, the handling of NULL values, and the subtle performance differences between the two forms.
This article explains the three InnoDB Buffer Pool page types—Free, Clean, and Dirty—their associated LRU, Flush, and Free linked lists, and how MySQL uses configurable parameters to balance memory usage, query speed, and data safety during flushing and checkpoint operations.
This article analyzes how MySQL/InnoDB applies row-level locks for DELETE and SELECT statements under various index configurations and isolation levels, explaining MVCC, current vs. snapshot reads, two‑phase locking, gap and next‑key locks, and the impact of primary, unique, non‑unique, and missing indexes.
This article explains the performance drawbacks of using UUIDs as primary keys in MySQL InnoDB tables, analyzes their impact on storage, I/O and CPU, and presents several mitigation strategies such as time‑ordered UUIDs, integer mapping, and alternative identifier schemes.
This article explains how MySQL InnoDB implements indexes with B+ trees, describes primary and secondary (clustered and non‑clustered) indexes, the concepts of row lookup, covering indexes, composite indexes, the left‑most prefix rule, index push‑down, and provides practical guidelines for creating and maintaining efficient indexes.
This article explains how using a large OFFSET in a MySQL LIMIT clause forces the server to scan hundreds of thousands of index and data pages, causing massive random I/O, and demonstrates a faster rewrite with an inner join that dramatically reduces buffer‑pool usage and execution time.
This article presents three common MySQL interview questions—whether query fields are case‑sensitive, how InnoDB implements transactions and logs, and the different binlog formats—along with detailed explanations, configuration examples, and SQL code snippets for each scenario.
This article provides a comprehensive overview of InnoDB's buffer pool, detailing its role as a data cache, the underlying data structures such as instances, chunks, and blocks, the page lifecycle from allocation to flushing, and discusses limitations of the default page‑cleaner implementation along with Percona's enhancements.
This article explains how InnoDB auto‑increment values behave when the highest ID is deleted, after a MySQL restart, and when IDs are manually set, including experiments and guidance on handling overflow.
This article explains how InnoDB stores user tables and indexes in .ibd files, describes the structure of tablespaces, pages, extents, header pages, XDES entries, INODE pages, and file segments, and shows how indexes allocate and free these internal structures as they grow and shrink.
This article explains the different forms of MySQL's COUNT function, compares COUNT(*), COUNT(1) and COUNT(column), reveals engine‑specific optimizations for MyISAM and InnoDB, and provides guidance on which form to use in practice.
This article explains the fundamentals of MySQL indexing, tracing the evolution from binary search trees and balanced AVL trees to B‑trees and B+‑trees, and details how InnoDB implements clustered and non‑clustered indexes, including search processes and performance considerations.
This article explains why MySQL uses B+‑tree indexes by tracing the evolution from binary search trees through balanced trees and B‑trees, detailing the structure of clustered and non‑clustered indexes in InnoDB and illustrating how data is searched using these indexes.
This article explains the internal representation and meaning of MySQL Handler_read_* status variables, demonstrates how InnoDB implements each handler, and shows practical query tests that illustrate how these counters reflect full table scans, index scans, range scans, and join operations.
This article explains the MySQL Clone plugin introduced in version 8.0.17, describes its underlying mechanism, installation and execution steps, outlines usage constraints and scenarios, and presents a detailed performance comparison with LVM snapshots and Xtrabackup under various workloads.
This article explores MySQL's hidden rowid concept, demonstrates how to observe its existence, explains its relationship with primary keys, highlights the risks of primary‑key misuse, and provides a step‑by‑step test that reveals rowid's potential overflow bottleneck.
This article examines a MySQL performance problem where frequent requests become unresponsive, analyzes processlist, system I/O/CPU metrics, and pstack traces to identify InnoDB thread concurrency and concurrency tickets as the root cause, then explains the relevant parameters, configuration guidelines, and a simulated test to demonstrate the solution.
This article explains the new NOWAIT and SKIP LOCKED keywords introduced in MySQL 8.0.1, describes their background, functionality, and internal implementation, and demonstrates their practical impact on lock‑wait scenarios through a fictional flash‑sale case study with code examples.
This article provides a comprehensive guide to MySQL InnoDB tablespace encryption, covering its architecture, supported plugins, configuration steps, key rotation, limitations, encrypted table operations, import/export procedures, and backup/restore methods using mysqlbackup and innobackupex.
The article describes how to migrate a multi‑gigabyte InnoDB table from a pre‑production MySQL 5.7 instance to production using the transportable tablespace feature, detailing the step‑by‑step procedure, performance benefits, and the specific limitations of this method.
This article explains the fundamentals of Multi-Version Concurrency Control (MVCC), compares its implementation in PostgreSQL and InnoDB, and highlights key differences in version storage, transaction handling, vacuuming, and index updates.
MLOG_CHECKPOINT is a mechanism in MySQL InnoDB crash recovery that ensures complete mapping between space IDs and file paths by supplementing missing MLOG_FILE_NAME records, addressing gaps that could occur between checkpoints and subsequent file modifications.
This weekly MySQL community newsletter highlights September 2019 DB‑Engines rankings, offers free Mycat diagnosis, summarizes DBLE and DTLE development updates, and showcases original technical articles on WRITESET parallel replication, InnoDB primary‑key optimization, MySQL 8.0 error‑log enhancements, and query optimization, inviting community feedback.
This article explains how InnoDB stores data using B‑Tree primary keys, why explicit primary keys are essential, and compares ordered versus random insert patterns, illustrating their impact on page fill factor, index size, and query performance with practical sysbench examples.
This article explains how MySQL's InnoDB engine marks rows as deleted without freeing disk space, demonstrates the issue with 100,000 rows, and shows how the OPTIMIZE TABLE or ALTER TABLE commands can rebuild the table to reclaim space and improve performance.
This guide explains how to restore MySQL InnoDB tables and their dictionary metadata after accidental drops, corruption, or disk failures by using the undrop‑for‑innodb toolkit, parsing system tables, and executing a series of command‑line steps to rebuild schema and data.
This article explains MySQL’s fundamental concepts, distinguishing databases from instances, outlines the three‑layer MySQL architecture, and dives deep into InnoDB’s storage hierarchy—from tablespaces, pages, and row formats to .frm/.ibd files, record overflow handling, and the B+‑tree index structures that power fast queries.
This article explains the storage capacity of InnoDB B+‑tree indexes by detailing page size, record size, pointer calculations, tree height effects, and real‑world verification using page‑level metadata, showing that a typical B+‑tree can hold tens of millions of rows with only 1‑3 I/O operations.
This article explains how InnoDB’s 16 KB pages, row size assumptions, and B+‑tree node capacities combine to allow roughly 20 million rows per tree, demonstrates how to calculate tree height from page metadata, and shows why MySQL chooses B+‑trees for primary‑key indexes.
This article explains InnoDB's Multi-Version Concurrency Control (MVCC) architecture, detailing row formats, undo log types, ReadView visibility rules, purge processes, and related concepts such as semi-consistent reads and index condition pushdown, with code examples and diagrams illustrating each mechanism.
This article explains what huge pages are, why they can improve memory performance, provides step‑by‑step instructions to enable them for MySQL on CentOS, shows how to verify the configuration, and shares test results that reveal little performance gain.
This weekly digest highlights the August MySQL ranking surge, Percona XtraBackup 8.0.7 features, free Mycat diagnostic support, DBLE and DTLE weekly reports, and several in‑depth technical articles covering MySQL cloning, group replication, charset performance, ZooKeeper deployment, and InnoDB index construction.
Since MySQL 5.7 InnoDB builds secondary indexes using a bottom‑up, sorted‑index approach, the article explains the three build phases, presents a step‑by‑step B‑tree construction example with SQL code, and discusses the innodb_fill_factor setting, its impact, advantages, and drawbacks.
This article demonstrates how to install and verify the MySQL 8.0.17 clone plugin, create privileged clone users on both donor and recipient servers, configure cloning parameters, execute a full instance clone, set up replication with CHANGE MASTER, and discusses the plugin's limitations such as InnoDB‑only support and DDL restrictions.
This article explains why MySQL can exhaust disk space when implicit temporary tables grow too large, describes how memory limits and storage‑engine choices affect their creation, and provides practical configuration and query‑optimization techniques to avoid service interruptions.
This article explains how the MySQL 8.0 CLONE plugin simplifies creating reliable replica instances by installing the plugin, granting necessary privileges, executing the CLONE SQL statement, monitoring progress via performance_schema, and verifying successful completion of all clone stages.
