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8.5.8 Optimizing InnoDB Configuration Variables

Different settings work best for servers with light, predictable loads, versus servers that are running near full capacity all the time, or that experience spikes of high activity.

Because the InnoDB storage engine performs many of its optimizations automatically, many performance-tuning tasks involve monitoring to ensure that the database is performing well, and changing configuration options when performance drops. See Section 14.16, “InnoDB Integration with MySQL Performance Schema” for information about detailed InnoDB performance monitoring.

For a list of the most important and most recent InnoDB performance features, see Section 14.1.1, “Features of the InnoDB Storage Engine”. Even if you have used InnoDB tables in prior versions, these features might be new to you, because they are from the InnoDB Plugin. The Plugin co-existed alongside the built-in InnoDB in MySQL 5.1, and becomes the default storage engine in MySQL 5.5 and higher.

The main configuration steps you can perform include:

  • Enabling InnoDB to use high-performance memory allocators on systems that include them. See Section 14.6.3, “Configuring the Memory Allocator for InnoDB”.

  • Controlling the types of DML operations for which InnoDB buffers the changed data, to avoid frequent small disk writes. See Section 14.6.4, “Configuring InnoDB Change Buffering”. Because the default is to buffer all types of DML operations, only change this setting if you need to reduce the amount of buffering.

  • Turning the adaptive hash indexing feature on and off using the innodb_adaptive_hash_index option. See Section, “Adaptive Hash Indexes” for more information. You might change this setting during periods of unusual activity, then restore it to its original setting.

  • Setting a limit on the number of concurrent threads that InnoDB processes, if context switching is a bottleneck. See Section 14.6.5, “Configuring Thread Concurrency for InnoDB”.

  • Controlling the amount of prefetching that InnoDB does with its read-ahead operations. When the system has unused I/O capacity, more read-ahead can improve the performance of queries. Too much read-ahead can cause periodic drops in performance on a heavily loaded system. See Section, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)”.

  • Increasing the number of background threads for read or write operations, if you have a high-end I/O subsystem that is not fully utilized by the default values. See Section 14.6.6, “Configuring the Number of Background InnoDB I/O Threads”.

  • Controlling how much I/O InnoDB performs in the background. See Section 14.6.7, “Configuring the InnoDB Master Thread I/O Rate”. The amount of background I/O is higher than in MySQL 5.1, so you might scale back this setting if you observe periodic drops in performance.

  • Controlling the algorithm that determines when InnoDB performs certain types of background writes. See Section, “Configuring the Rate of InnoDB Buffer Pool Flushing”. The algorithm works for some types of workloads but not others, so might turn off this setting if you observe periodic drops in performance.

  • Taking advantage of multicore processors and their cache memory configuration, to minimize delays in context switching. See Section 14.6.8, “Configuring Spin Lock Polling”.

  • Preventing one-time operations such as table scans from interfering with the frequently accessed data stored in the InnoDB buffer cache. See Section, “Making the Buffer Pool Scan Resistant”.

  • Adjusting log files to a size that makes sense for reliability and crash recovery. InnoDB log files have often been kept small to avoid long startup times after a crash. Optimizations introduced in MySQL 5.5.4 speed up certain steps of the crash recovery process. In particular, scanning the redo log and applying the redo log are faster due to improved algorithms for memory management. If you have kept your log files artificially small to avoid long startup times, you can now consider increasing log file size to reduce the I/O that occurs due recycling of redo log records.

  • Configuring the size and number of instances for the InnoDB buffer pool, especially important for systems with multi-gigabyte buffer pools. See Section, “Using Multiple Buffer Pool Instances”.

  • Increasing the maximum number of concurrent transactions, which dramatically improves scalability for the busiest databases. See Section 14.5.5, “InnoDB Rollback Segments”. Although this feature does not require any action during day-to-day operation, you must perform a slow shutdown during or after upgrading the database to MySQL 5.5 to enable the higher limit.

  • Moving purge operations (a type of garbage collection) into a background thread. See Section 14.6.9, “Configuring InnoDB Purge Scheduling”. To effectively measure the results of this setting, tune the other I/O-related and thread-related configuration settings first.

  • Reducing the amount of switching that InnoDB does between concurrent threads, so that SQL operations on a busy server do not queue up and form a traffic jam. Set a value for the innodb_thread_concurrency option, up to approximately 32 for a high-powered modern system. Increase the value for the innodb_concurrency_tickets option, typically to 5000 or so. This combination of options sets a cap on the number of threads that InnoDB processes at any one time, and allows each thread to do substantial work before being swapped out, so that the number of waiting threads stays low and operations can complete without excessive context switching.

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