[MDEV-329] MariaDB 5.5 does not use fdatasync() Created: 2012-06-08  Updated: 2012-06-08  Resolved: 2012-06-08

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: 5.5.24
Fix Version/s: 5.5.25

Type: Bug Priority: Blocker
Reporter: Kristian Nielsen Assignee: Kristian Nielsen
Resolution: Fixed Votes: 0
Labels: None


 Description   

I discovered a serious problem in 5.5 related to fsync (5.3 and below appears
not affected).

By default, we do not run any fsync at all. This is because the
--debug-no-sync option is incorrectly enabled by default.

This problem was introduced here:

revid:sergii@pisem.net-20111212225840-8aotf02a1alw1gta

  • {"sync_sys", 0, - "Enable system sync calls. Disable only when running tests or debugging!", - &opt_sync, &opt_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

    ,
    +

    {"debug-no-sync", 0, + "Disables system sync calls. Only for running tests or debugging!", + &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

    ,

The option was renamed and the meaning was reversed - but the default was left
unchanged, effectively reversing the default.

We need to fix this ASAP, as it causes data loss / silent corruption when the
host machine crashes.

There is an additional problem that even with --debug-no-sync=0, we are using
fsync(), not fdatasync() as we should. There is code to use fdatasync(), but
apparently availability of fdatasync() is not correctly detected by
cmake. This is also a quite serious issue; one one machine I tested with a
good RAID controller, fdatasync() is 2.5 times faster than fsync().

Work-around: pass --debug-no-sync=0 in config or on command line (but this will not fix fdatasync() performance problem).

 Comments   
Comment by Kristian Nielsen [ 2012-06-08 ]

This patch seems to fix it:

=== modified file 'config.h.cmake'
— config.h.cmake 2012-04-19 02:02:28 +0000
+++ config.h.cmake 2012-06-08 08:49:30 +0000
@@ -150,6 +150,7 @@
#cmakedefine HAVE_FCNTL 1
#cmakedefine HAVE_FCONVERT 1
#cmakedefine HAVE_FDATASYNC 1
+#cmakedefine HAVE_DECL_FDATASYNC 1
#cmakedefine HAVE_FESETROUND 1
#cmakedefine HAVE_FINITE 1
#cmakedefine HAVE_FP_EXCEPT 1

=== modified file 'sql/mysqld.cc'
— sql/mysqld.cc 2012-05-21 18:54:41 +0000
+++ sql/mysqld.cc 2012-06-08 08:49:06 +0000
@@ -6161,7 +6161,7 @@ struct my_option my_long_options[]=
#endif

{"debug-no-sync", 0, "Disables system sync calls. Only for running tests or debugging!", - &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 1, 0, 0, 0, 0, 0}

,
+ &my_disable_sync, &my_disable_sync, 0, GET_BOOL, NO_ARG, 0, 0, 0, 0, 0, 0},
#ifdef HAVE_REPLICATION
{"debug-sporadic-binlog-dump-fail", 0,
"Option used by mysql-test for debugging and testing of replication.",

Comment by Kristian Nielsen [ 2012-06-08 ]

Pushed to lp:maria/5.5

Generated at Thu Feb 08 06:27:56 UTC 2024 using Jira 8.20.16#820016-sha1:9d11dbea5f4be3d4cc21f03a88dd11d8c8687422.