RDS for MySQL
RDS for MySQL
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RDS for MySQLKernel functionsPerformanceSupport for using fdatasync
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Support for using fdatasync
Copy pageDownload PDFSupport for using fdatasync
This topic provides information about the fdatasync call for MySQL 5.7 instances in RDS for MySQL.
Background
InnoDB's redo log/doublewrite buffer currently uses the fsync system call to flush data to disk, an operation that includes flushing both file metadata and file data. In write scenarios with fixed-size files, such as the redo log/doublewrite buffer, refreshing file metadata like the last modification time is unnecessary. The fdatasync system call can avoid constantly flushing file metadata to the storage device, thereby reducing write overhead.
MySQL 8.0 introduced support for using the fdatasync system call instead of fsync for flushing data to disk, and this optimization is enabled by default in version 8.4 and later. RDS for MySQL has backported this optimization from MySQL 8.0 to MySQL 5.7.
Supported version
MySQL 5.7, kernel version MySQL 5.7 20250615 or later.
Use cases
Suitable for scenarios with high write pressure that require frequent synchronous flushing of redo logs and the doublewrite buffer.
Performance data
In sysbench-write-only high-concurrency continuous write scenarios, QPS performance can be improved by about 5%.
Instructions
In the RDS for MySQL console, set the loose_innodb_use_fdatasync parameter to on to enable the fdatasync disk flushing optimization for the instance. For more information about modifying parameters, see Modifying parameters.
Parameter name | Default value | Does it need instance restart to take effect? | Value range | Scope | Parameter description |
loose_innodb_use_fdatasync | OFF | No | [ON|OFF] | Global | Specifies whether to use the fdatasync system call to flush data to disk. |
Last updated: 2026.05.28 15:17:54
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