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IDS Forum

Re: Performance issue

Posted By: Art Kagel
Date: Monday, 8 June 2015, at 3:57 p.m.

In Response To: Re: Performance issue (Marcus Haarmann)

Check the RAID10 block/stripe size. If it is very large, then many IOs may
be hitting only a single pair of drives rather than being spread across the
array.

Art

Art S. Kagel, President and Principal Consultant
ASK Database Management
www.askdbmgt.com

Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions
and do not reflect on the IIUG, nor any other organization with which I am
associated either explicitly, implicitly, or by inference. Neither do
those opinions reflect those of other individuals affiliated with any
entity with which I am affiliated nor those of the entities themselves.

On Mon, Jun 8, 2015 at 3:48 PM, Marcus Haarmann <marcus.haarmann@midoco.de>
wrote:

> Hi Art,
>
> we have SAS harddisks with Raid10, connected with Fibre channel 8GBit.
> The array is directly attached, no switches.
> All partitions are raw with an lvm2 layer as partitioning help.
> KAIO is worth a review, but first we will run without btree cleaner to
> check
> for influences
> one at a time.
> Logs are on a separate partition, but I think the admin did not put it on
> separate disks.
> We have to check the SAN layout, which I did not set up.
> I will check if the indexes are fully separated, I doubt it, because the
> primary/foreign keys
> are most probably in the data dbs.
> And yes, we are running without any virtualization, directly on the
> machine,
> no virtual drivers etc.
> This hardware is dedicated to that Informix instance, also the disk array
> is
> only serving this instance,
> so any external influence should be reduced to a minimum.
> As always, there could be more buffering, but growth edition has some
> limits
> here ...
>
> Marcus Haarmann
>
> ----- Ursprüngliche Mail -----
>
> Von: "Art Kagel" <art.kagel@gmail.com>
> An: ids@iiug.org
> Gesendet: Montag, 8. Juni 2015 18:24:20
> Betreff: Re: Performance issue [35236]
>
> Marcus:
>
> Spokey may have nailed it, the BT Scanner activity is certainly a
> possibility, I also see that the first stack trace includes adding a new
> key to an index which may have triggered that index to go over the hill and
> be placed on the Btree hot list. It's worth looking into what the BT
> Scanner is doing at the time of the next block incident.
>
> Personally, I want to blame IO. You say: "the disk array is very fast, I/O
> should not be the problem" but that doesn't mean much. Is it possible that
> the chunks are on a SAN/NAS that is being shared with other applications
> that may be interfering/contending for head placement or bandwidth? What
> are the underlying disk structures (RAID level, etc.)? How is your read
> ahead configured? Are the chunks for the logical and physical logs on the
> same disk structures as each other? As the data? As the index? Are you
> simply contending with yourself? Are the chunks RAW or COOKED? Is
> DIRECT_IO enabled? Is KAIO configured with enough OS resources to cope?
>
> Art
>
> Art S. Kagel, President and Principal Consultant
> ASK Database Management
> www.askdbmgt.com
>
> Blog: http://informix-myview.blogspot.com/
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and do not reflect on the IIUG, nor any other organization with which I am
> associated either explicitly, implicitly, or by inference. Neither do
> those opinions reflect those of other individuals affiliated with any
> entity with which I am affiliated nor those of the entities themselves.
>
> On Mon, Jun 8, 2015 at 11:42 AM, Marcus Haarmann <
> marcus.haarmann@midoco.de>
> wrote:
>
> > Hi experts,
> >
> > we are encountering a performance problem on one of our database systems,
> > which happens periodically,
> > not limited to a specific high load.
> > The effect is that all our application servers are blocked with some
> > transactions (which are committing
> > at this time), until 20-30 seconds later all the threads are unblocked
> all
> > of
> > a sudden.
> > (in the same millisecond, spread over all client machines).
> > The common thing is that all these threads have a connection to a
> specific
> > database instance and
> > have all done mostly read-only work (within a XA transaction, which is
> > necessary to support multiple
> > datasources).
> > Since this effect is not really happening really regularly, but between
> 4-8
> > times spread over the day,
> > it is not easy to find out what is the main blocker here.
> >
> > We have now done some measurements in the application to get the correct
> > time
> > when the situation occurs
> > and executed a script each 10 seconds to get some status information from
> > the
> > common DB instance.
> > The script put a timestamp in a log and executed onstat -g sql, followed
> by
> > onstat -g stk
> >
> > What seems to be interesting:
> > 1) online.log does not show anything when the effect occurs (no
> > checkpoint, no
> > full log, no entry at all)
> > 2) What we found as common output ist the following thread during the
> > blocking
> > period:
> >
> > Stack for thread: 1101943 sqlexec
> > base: 0x00000003aff07000
> > len: 135168
> > pc: 0x00000000012ce881
> > tos: 0x00000003aff25190
> > state: sleeping
> > vp: 1
> >
> > 0x00000000012ce881 (/opt/informix/bin/oninit) yield_processor_mvp
> > 0x00000000012d76df (/opt/informix/bin/oninit) mt_yield
> > 0x0000000000e975a7 (/opt/informix/bin/oninit) logm_flush
> > 0x0000000000d526ef (/opt/informix/bin/oninit) logflush
> > 0x0000000000d21e55 (/opt/informix/bin/oninit) bfphysflush
> > 0x0000000000d22a37 (/opt/informix/bin/oninit) bfphyslogx
> > 0x0000000000cfe082 (/opt/informix/bin/oninit) btadditem
> > 0x0000000000d00382 (/opt/informix/bin/oninit) rsbtadditem
> > 0x00000000013be6b0 (/opt/informix/bin/oninit) fm_idxinsert
> > 0x000000000139bdea (/opt/informix/bin/oninit) fmwrite
> > 0x0000000000688d82 (/opt/informix/bin/oninit) aud_sqiswrite
> > 0x000000000082a233 (/opt/informix/bin/oninit) chkrowcons
> > 0x00000000007da790 (/opt/informix/bin/oninit) addone
> > 0x00000000007de57a (/opt/informix/bin/oninit) insone_next
> > 0x00000000008399b7 (/opt/informix/bin/oninit) doinsert
> > 0x00000000005af784 (/opt/informix/bin/oninit) excommand
> > 0x00000000009abfd0 (/opt/informix/bin/oninit) sq_execute
> > 0x0000000000a6a3fb (/opt/informix/bin/oninit) sqmain
> > 0x00000000013dbe3b (/opt/informix/bin/oninit) spawn_thread
> > 0x00000000013151c0 (/opt/informix/bin/oninit) th_init_initgls
> > 0x00000000012e1a38 (/opt/informix/bin/oninit) startup
> >
> > This seems to be an insert, which triggers an index (btree) write, which
> > triggers a physical log flush.
> > (there have been many inserts between the blocking times, which did not
> > trigger such a flush.
> > This only occurs sometimes.)
> >
> > 3) also a very high number of threads does the following:
> >
> > Stack for thread: 905431 sqlexec
> > base: 0x00000003a7b48000
> > len: 135168
> > pc: 0x00000000012ce881
> > tos: 0x00000003a7b67250
> > state: cond wait
> > vp: 8
> >
> > 0x00000000012ce881 (/opt/informix/bin/oninit) yield_processor_mvp
> > 0x00000000012e1216 (/opt/informix/bin/oninit) mt_fast_wait
> > 0x0000000000d52e82 (/opt/informix/bin/oninit) logwrite
> > 0x0000000000e99b9e (/opt/informix/bin/oninit) logm_write
> > 0x0000000000d504bb (/opt/informix/bin/oninit) logputx
> > 0x0000000000ccd40f (/opt/informix/bin/oninit) rscommit
> > 0x0000000000de2a6b (/opt/informix/bin/oninit) xa_commit
> > 0x00000000009dd04b (/opt/informix/bin/oninit) ifx_common_xcommit
> > 0x00000000009dd39d (/opt/informix/bin/oninit) sq_xcommit
> > 0x0000000000a6a3fb (/opt/informix/bin/oninit) sqmain
> > 0x00000000013dbe3b (/opt/informix/bin/oninit) spawn_thread
> > 0x00000000013151c0 (/opt/informix/bin/oninit) th_init_initgls
> > 0x00000000012e1a38 (/opt/informix/bin/oninit) startup
> >
> > This seems to be one of the threads blocking in commit. The reason is
> > obviously a logwrite call,
> > which it is waiting for. We have 95 threads a this time which have a
> > logwrite
> > stack member !
> >
> > Now my question: How can we prevent this flushing ? Or make it happen
> > faster ?
> > Or are we on the wrong way when looking at the source of the problem ?
> > What is really happening during logwrite ? Since the hardware is
> relatively
> > new,
> > and the disk array is very fast, I/O should not be the problem.
> >
> > We have here: IDS 11.70FC8XB8GE running on Linux x64, using huge memory
> > pages.
> >
> > Machine has 24GB Ram, Database uses ~15GB.
> > Checkpoints are done on 3-4 seconds, flush time 1.5-2.4 seconds (this
> > cannot
> > trigger 20 seconds of
> > blocking from my point of view).
> > onstat -F shows only chunk writes. onstat -p shows 99,8% read cached and
> > 86,47% write cached.
> > Physical log is 5GB, rarely used > 5%
> > Checkpoints occur each 300sec, no other triggers than interval.
> >
> > The machine is paired with a secondary instance via HDR. HDR pair was up
> > and
> > running without any trace of
> > "real" activity (checkpoints 1 second).
> >
> > Any idea will be appreciated, we cannot file a bug, since we are not able
> > to
> > reproduce the behaviour
> > or even present an onstat -a output.
> > Yes, the instance is loaded very high, but we have other instances with
> > equal
> > or higher load, which
> > are not behaving like this.
> >
> > Marcus Haarmann
> >
> >
> >
> >
>
>
> *******************************************************************************
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> >
> >
>
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>
>
> *******************************************************************************
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