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IDS Forum

Re: Antw: Long Transaction

Posted By: Jonathan Leffler
Date: Tuesday, 23 September 2003, at 8:31 p.m.

In Response To: Re: Antw: Long Transaction (Mark Scranton )





Or the server adds dynamic logs before hanging - depending on version (9.30
up?) and configuration (dynamic logs enabled).

--
Jonathan Leffler (jleffler@us.ibm.com)
STSM, Informix Database Engineering, IBM Data Management
4100 Bohannon Drive, Menlo Park, CA 94025
Tel: +1 650-926-6921 Tie-Line: 630-6921
"I don't suffer from insanity; I enjoy every minute of it!"




|---------+---------------------------->
| | Mark |
| | Scranton/Denver/I|
| | BM@IBMUS |
| | Sent by: |
| | forum.subscriber@|
| | iiug.org |
| | |
| | |
| | 09/23/2003 02:08 |
| | PM |
|---------+---------------------------->
>---------------------------------------------------------------------------------------------------------------------------------------------|
| |
| To: ids@iiug.org |
| cc: |
| Subject: Re: Antw: Long Transaction [1916] |
>---------------------------------------------------------------------------------------------------------------------------------------------|




Regarding long transactions...

A long transaction is defined as "1. still open (uncommitted), and 2.
starting in the oldest log". One of the sanity checks we do at log switch
is to determine if the logs full surpasses the LTXHWM, defaulting to 50%.
If so, we "take over" the long transaction(s), and start rolling it back.
While this in question transaction (the one you have dug into a bit) is
running, all of the other transactions are there as well, and in turn, also
filling up log space. So the "size" of this transaction isn't the only
factor - everyone contributes to filling the logs.

The question comes up ... "are long transactions time-based, or
activity-based?" The answer here is "yes". Imagine the scenario that
someone inserts one row (and it's logged to the oldest log). He then does
nothing. Meanwhile, the other transactions fill the logs to 50%...this
one-row insert will be a long transaction..it's still open, and it started
in the oldest log. The reason we have to deal with it is because when we
circle around to re-use that log, we can't since there is an open
transaction in it. So we attempt to roll it back by placing CLR
(compensation log records) in the logical logs to undo what he did...in
this case, just 1 CLR for 1 row. Meanwhile, people are still writing to the
logs. If we cross the LTXEHWM (e is for exclusive), AND we are still
rolling back a transaction (doubtful in this scenario, but possible), we
give "exclusive" access to the rolling back transaction, effectively
suspending the other "normal" txs. If we can't get the rollback done within
the remaining log space, we circle and can't write to the oldest log, and
the engine hangs.

HTH -
Mark.

Mark Scranton
Principal Consultant/Teacher
IBM Denver

IBM Software Group - Data Management
Office: 303-773-5067
Cell: 303-929-0914
email: mscranto@us.ibm.com





"Andreas.KUT...."

<andreas.kutsche@ To: ids@iiug.org

spar.at> cc:

Sent by: Subject: Antw: Long
Transaction [1881]
forum.subscriber@

iiug.org



09/16/2003 05:52

AM






----LNX_Tue_Sep_16_2003_13:49:21_V3.33--
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

>Datum: 2003.09.16 12:29:47
>Sender: IAN LOGAN <ian.logan@straker.com>
>
>I am experiencing a long transaction problem when running a stored pro
>cedure.
>
>The procedure is taking rows from a view, inserting them into a table an=
d
>then updating them. The table is used for reporting purposes and contain=
s about 60,000
>rows in all, but only about 1000 rows are involved when the procedure is=

>run. The procedure runs fine for 3 months worth of data but fails with e=
rror 458
>(long trans) for longer time spans ie more rows.
>
>3. Logfiles 99, Logsize 80MB
=

onstat -l shows 99 logfiles with 80 MB each? Therefore you have 8 GB lo=
gspace - that's a lot!?
or is 80 MB the sum of all your logfiles?
=

Anyway, what amount of data do you expect to be worked on in one transact=
ion roughly ?
row size \* # inserts + row size \* # updates + something extra f=
or indexes ?
=

> 4. LTXHWM 50
=

LTXHWM - that means your transactions must be smaller than half of your l=
ogspace (if they are
running alone on the server) ? NEVER touch the LTXHWM without readingthe =
documentation
about it!
=

If you think your transaction should fit into the (half) logspace: Isyour=
transaction running alone (exclusive),
or are running a lot of other transactions at the same time? They share t=
he logspace! If other transactions
run simultaniously - can you run your procedure exclusively to check if i=
t fails in that case, too?
=

> 6. maxlogsp 6050192 (queried from syssesprof) This seems to indicate th=
at I am not hitting the logs limit
=

Maybe it's a 'time' problem (or 'total load' problem): Your transaction i=
s running very long and other
transactions fill the logspace?
=

=

Check your procedure - does it use indices where appropriate (for updates=
etc.) ?
=

Regards,
Andreas

------------------------------------------------
SPAR Oesterreichische Warenhandels-AG
Hauptzentrale
Europastra=DFe 3
A-5015 Salzburg
=

Telefon : +43 662 4470 24423
E-Mail : Andreas.KUTSCHE@spar.at
Internet: http://www.spar.at
------------------------------------------------

=


----LNX_Tue_Sep_16_2003_13:49:21_V3.33----







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