Percona Server 5.7 manual is misleading for innodb_flush_method

[Valerii Kravchuk]

Manual for Percona Server 5.7 (https://www.percona.com/doc/percona-server/5.7/scalability/innodb_io.html#innodb_flush_method) says:

"ALL_O_DIRECT: use O_DIRECT to open both data and log files, and use fsync() to flush the data files but not the log files. This option is recommended when InnoDB log files are big (more than 8GB), otherwise there might be even a performance degradation. Note: When using this option on ext4 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."

There are two problems with this text.

First, ALL_O_DIRECT does not work, server does not start with this value set and everything else default (unlike in 5.6), see my last comment to https://bugs.launchpad.net/percona-server/+bug/1131949

Second is that innodb_log_block_size variable it suggests to set does NOT exist in 5.7:

[root@centos ~]# mysql -uroot -e "show variables like 'innodb_log%'"
+-----------------------------+----------+
| Variable_name | Value |
+-----------------------------+----------+
| innodb_log_buffer_size | 16777216 |
| innodb_log_checksums | ON |
| innodb_log_compressed_pages | ON |
| innodb_log_file_size | 50331648 |
| innodb_log_files_in_group | 2 |
| innodb_log_group_home_dir | ./ |
| innodb_log_write_ahead_size | 8192 |
+-----------------------------+----------+
[root@centos ~]# mysql -uroot -e "show variables like 'version%'"
+-------------------------+---------------------------------------------------+
| Variable_name | Value |
+-------------------------+---------------------------------------------------+
| version | 5.7.10-3-log |
| version_comment | Percona Server (GPL), Release 3, Revision 63dafaf |
| version_compile_machine | x86_64 |
| version_compile_os | Linux |
+-------------------------+---------------------------------------------------+

[Laurynas Biveinis (laurynas-biveinis)]

The first problem is tracked at https://bugs.launchpad.net/percona-server/+bug/1529885.

This bug is then about the second problem, which is a documentation bug.

[Hrvoje Matijakovic (hrvojem)]

Fixed here: https://github.com/percona/percona-server/pull/381

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-968