Improved InnoDB I/O Scalability¶
Because InnoDB is a complex storage engine it must be configured properly in order to perform at its best. Some points are not configurable in standard InnoDB. The goal of this feature is to provide a more exhaustive set of options for XtraDB.
Version Specific Information¶
* 8.0.12-1: The feature was ported from *Percona Server for MySQL* 5.7.
Note
Implemented in Percona Server for MySQL 8.0.13-4, max checkpoint age has been removed because the information is identical to log capacity.
System Variables¶
innodb_flush_method¶
| Option | Description |
|---|---|
| Command-line | Yes |
| Config file | Yes |
| Scope | Global |
| Dynamic | No |
| Data type | Enumeration |
| Default | NULL |
| Allowed values | fsync, O_DSYNC, O_DIRECT, O_DIRECT_NO_FSYNC, littlesync, nosync |
The following values are allowed:
* `fdatasync`: use `fsync()` to flush data, log, and parallel doublewrite files.
* `O_SYNC`: use `O_SYNC` to open and flush the log and parallel doublewrite files; use `fsync()` to flush the data files. Do not use `fsync()` to flush the parallel doublewrite file.
* `O_DIRECT`: use O_DIRECT to open the data files and `fsync()` system call to flush data, log, and parallel doublewrite files.
* `O_DIRECT_NO_FSYNC`: use O_DIRECT to open the data files and parallel doublewrite files, but does not use the `fsync()` system call to flush the data files, log files, and parallel doublewrite files. Do not use this option for the *XFS* file system.
* `ALL_O_DIRECT`: use O_DIRECT to open data files, log files, and parallel doublewrite files
and use `fsync()` to flush the data files but not the log files or
parallel doublewrite files. This option is recommended when *InnoDB* log files are big (more than 8GB), otherwise, there may be performance degradation.
Note
When using this option on ext4, the filesystem variable innodb_log_block_size should be set to 4096 (default log-block-size in ext4) in order to avoid the unaligned AIO/DIO warnings.
Starting from Percona Server for MySQL 8.0.20-11, the innodb_flush_method affects doublewrite buffers exactly the same as in MySQL 8.0.20.
Status Variables¶
The following information has been added to SHOW ENGINE INNODB STATUS to confirm the checkpointing activity:
The max checkpoint age
The current checkpoint age target
The current age of the oldest page modification which has not been flushed to disk yet.
The current age of the last checkpoint
...
---
LOG
---
Log sequence number 0 1059494372
Log flushed up to 0 1059494372
Last checkpoint at 0 1055251010
Max checkpoint age 162361775
Checkpoint age target 104630090
Modified age 4092465
Checkpoint age 4243362
0 pending log writes, 0 pending chkp writes
...