Ok, after some experimenting and code inspection, this is the summary.
This is the logic that decides if mariadb 10.6.7 will try to use uring or not,
AT RUNTIME:
bool innodb_use_native_aio_default()
{
#ifdef HAVE_URING
utsname &u= uname_for_io_uring;
if (!uname(&u) && u.release[0] == '5' && u.release[1] == '.' &&
u.release[2] == '1' && u.release[3] >= '1' && u.release[3] <= '5' &&
u.release[4] == '.')
{
if (u.release[3] == '5') {
const char *s= strstr(u.version, "5.15.");
if (s || (s= strstr(u.release, "5.15.")))
if ((s[5] >= '3' || s[6] >= '0'))
return true; /* 5.15.3 and later should be fine */
}
io_uring_may_be_unsafe= u.release;
return false; /* working around io_uring hangs (MDEV-26674) */
}
#endif
return true;
}
As we can see, it depends on the RUNNING kernel, and details are in
https://jira.mariadb.org/browse/MDEV-26674
The jammy kernel is 5.15.0, which makes the above return false, meaning
io_uring is NOT used.
The focal kernel is 5.4.0, which makes the above return true, meaning
io_uring IS USED.
That's why running the jammy build of mariadb on a focal kernel attempts
to use io_uring. And this is what the current launchpad builders are:
focal kernel, with chroots for the ubuntu release they are building for.
And mariadbd is run in this env as part of the build-time tests.
Note the above is for RUNTIME decision: HAVE_URING is decided at build
time, and is not related to this bug.
If uring is used, then the memlock limit comes into play: it indeed
needs to be higher. stracing jammy's mariadb on the focal kernel shows
that io_uring_setup() failed with ENOMEM.
Quick reproducer:
- create a focal VM
- confirm ulimit -l value in that VM. I've been getting the value "64", but
anything lower than 256 will trigger the bug.
- inside that VM, create a jammy LXD
- iside that LXD, install mariadb-server. It will fail.
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https://bugs.launchpad.net/bugs/1970634
Title:
FTBFS: test failure due to low memlock limit
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