is TMPFS still highly experimental?

[Xin LI]

On Sun, Oct 2, 2011 at 3:33 PM, Ivan Voras <ivoras at freebsd.org> wrote:
> On 02/10/2011 07:27, Xin LI wrote:
>
>> The problem Ivan have asserted was not confirmed by anyone who have
>> swap configured properly.  Gleb have pointed out that it might be
>> related to a series of integer overflow by the way (he have also fixed
>> a lot of tmpfs issues by the way).
>
> Well, instead of guessing I can point you to the way I got the original
> situation - you said you have ZFS configured so it would be easy for you
> to check.
>
> You should to something like this:
>
>        - configure your system to the best of your abilities (but post what
> you did different from the defaults)

It's mostly "normal" configuration -- 6GB RAM, 14GB swap, ZFS as /usr;

The following sysctl tweaks were done to make postgresql start (these
are not scientific, just large enough to make it work):

kern.ipc.shmmax=4294967296
kern.ipc.shmall=1048576

>        - install postgresql (8.4+, but I don't think the version is
> important), configure it so it gets half the system memory or 2/3 the
> system memory for its shared_buffers.

Configured to half of system memory (3072MB).

# ipcs -a
Message Queues:
T           ID          KEY MODE        OWNER    GROUP    CREATOR
CGROUP                 CBYTES                 QNUM
QBYTES        LSPID        LRPID STIME    RTIME    CTIME

Shared Memory:
T           ID          KEY MODE        OWNER    GROUP    CREATOR
CGROUP         NATTCH        SEGSZ         CPID         LPID ATIME
DTIME    CTIME
m        65536      5432001 --rw------- pgsql    pgsql    pgsql
pgsql               6   3295936512         2130         2130 10:57:12
11:09:17 10:57:12

Semaphores:
T           ID          KEY MODE        OWNER    GROUP    CREATOR
CGROUP          NSEMS OTIME    CTIME
s        65536      5432001 --rw------- pgsql    pgsql    pgsql
pgsql              17 11:09:25 10:57:12
s        65537      5432002 --rw------- pgsql    pgsql    pgsql
pgsql              17 10:57:12 10:57:12

>        - install pgbench

Done.

>        - initialize pgbench so that the database definitely is larger than the
> entire memory you got (NOTE: THIS IS NOT A CONTRIVED TEST - lots of
> databases in practice are larger than the RAM in the server).

Initialized with pgbench -i -s 500 pgbench.

>        - run pgbench & observe the results.

pgbench -t 20000 -c 64 -S pgbench

Can't seem to reproduce:

# df -Httmpfs
Filesystem    Size    Used   Avail Capacity  Mounted on
tmpfs          10G     69k     10G     0%    /tmp

Any suggestions?

> This should create really bad contention problem for memory between
> postgresql and ZFS, which should manifest itself in tmpfs shrinking to 0
> bytes free.
>
> If you don't get this problem then great, it might be solved!
>
>
> (for more info on pgbench, see this:
> http://www.westnet.com/~gsmith/content/postgresql/pgbench-scaling.htm).
>
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-- 
Xin LI <delphij at delphij.net> https://www.delphij.net/
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