Question about MySQL and lwp_mutex_lock and lwp_mutex_wakeup

[Mariella Di Giacomo]

Hello,

I am running MySQL 4.0.5b 64 bits on a Solaris 2.8.
The server used has 8 CPUs.

MySQL DB has access (and menage) in that system 2DBs.
The first DB is only is accessed only through SELECTS and the
second one has been used for UPDATES and INSERTS.

Initially I was running a process that was updating the tables.
In the program there is no contention among tables and there is only
one process that executes UPDATES AND INSERTS.

Apparently as soon as people start accessing the other DB (quite heavily)
the time spent by MySQL in

lwp_mutex_wakeup
lwp_mutex_lock


increases a lot .

This is a screen shot taken with truss of the process in a certain timeframe.


______________________________________________________

signals ------------
SIGALRM 1
total: 1

syscall seconds calls errors
read 69.78 4597 594
write 26.41 1851
close .46 105
time 87.91 5096
lseek 6.44 276
alarm .00 1
fstat 17.10 1503
access .72 105
fcntl 22.59 1503
poll 1.89 105
lwp_sema_wait 4.88 562
lwp_sema_post 7.95 562
lwp_mutex_wakeup 30.89 3247
lwp_mutex_lock 31.17 2529
lwp_cond_wait .00 1 1
pread 2.73 137
pwrite 45.36 2361
signotifywait .00 1
accept 2.43 105
shutdown .99 105
getpeername .73 105
getsockname 2.18 105
getsockopt 22.55 1503
setsockopt 26.88 1713
lwp_sigtimedwait .07 1
------- ------ ----
sys totals: 412.11 28179 595
usr time: .48
elapsed: 96.46

______________________________________________________

As soon as all the shutdown all the users from the DB that is used for only SELECT,
now the same process that runs MySQL updates on the other DB has hardly ever
lwp_mutex_wakeup
lwp_mutex_lock
calls.


Could someone, please, help me trying to understand why that is the behavior ?

Thanks a lot,

Mariella



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