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IDS Forum

Re: Problem with ONBAR: unusually slow on IDS 11.5

Posted By: Art Kagel
Date: Wednesday, 23 February 2011, at 7:06 p.m.

In Response To: Problem with ONBAR: unusually slow on IDS 11.50.FC (Khaled Bentebal)

I suspect that sysmaster isn't the problem, it is that your Tablespace
Tablespaces have too many extents. This can happen if you have lots of
dbspaces and a large number of tables, indexes, and fragments of tables and
indexes spread across them.

Every table in the system has a partition header page, also known as its
Tablespace Tablespace page. The descriptive and performance profile data
from these header pages are what are displayed by the sysmaster pseudo
tables sysptnhdr and sysactptnhdr (the former is just an older version of
the later included for backward compatibility). The Tablespace Tablespace
is treated as a table by the server with a partition in each dbspace which
holds the partition header pages for all tables, indexes, and fragments of
tables and indexes that are resident in that dbspace. What has happened
is that when you creating your tables and indexes the Tablespace Tablespace
became fragmented within each dbspace. Since this is not an 'actual' table,
it has no indexes, so searching it, as onbar does with the query you posted,
requires a sequential scan of all of those fragmented extents. By default,
the initial and next extent sizes for the Tablespace Tablespace for the root
chunk are 250 K and 4 K respectively. Other dbspaces default to even lower
values: 50 pages (using the dbspace's pagesize) and 4 pages unless you
modified those values with the onspaces -ef and -en options when you created
the dbspaces. There are now two ONCONFIG parameters, TBLTBLFIRST and
TBLTBLNEXT, that control the initial extent sizing for this structure in the
root dbspace, however, it is only effective for the root dbspace when the
server is initialized.

You can determine how big these parameters need to be set to for each
dbspace by using the following select:

select dbsname, count(*) as num_extents, sum( size * pagesize / 1024) as
total_kb
from sysextents se, sysdbspaces sd
where se.tabname matches 'TBL*'

and se.dbsname = sd.name
group by 1
order by 1;

So, what you have to do to fix this is to unload all of your data from that
server, modify TBLTBLFIRST and TBLTBLNEXT in the ONCONFIG file, drop and
recreate all of your dbspaces specifying appropriate extent sizing, and
reload the data. Alternatively you could create new dbspaces with
appropriate extent sizing and use ALTER FRAGMENT FOR TABLE <tabname> INIT...
to move each table to one of the new dbspaces then drop the old ones once
they are empty. However, this latter procedure will not allow you do drop
any dbspaces that contain a database's catalog tables.

Once that is done, the Tablespace Tablespace entries should now be far more
contiguous and the onbar statement will run much faster.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
IIUG Board of Directors (art@iiug.org)
Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions and
do not reflect on my employer, Advanced DataTools, 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 Wed, Feb 23, 2011 at 5:52 PM, Khaled Bentebal <
khaled.bentebal@consult-ix.fr> wrote:

> Hi,
>
> A client of ours is runnning IDS 11.50.FC5 on AIX and is facing a
> problem with a backup running ONBAR.
>
> It runs fine on several instances on different machines, but is very
> slow on one instance. All of the instances are setup the same way along
> the same model and the same ONCONFIG.
>
> ONBAR runs a particular query before performing the backup:
> *select ( sum ( npused ) ) from sysdbspaces as D , sysptnhdr as P where
> D.dbsnum = TRUNC ( P.partnum/1048576 ) and name = ? *
>
> This query goes on for ever (*few hours*). We tried to run a query on
> sysptnhdr by itself and sysdbspaces also by itself. It seems that the query
> on
> sysptnhdr is very very slow. The same query runs very fast (instantanious)
> on
> the other instances.
> We tried to rebuild the sysmaster databse, but nothing came out it.
>
> Here is more info on this session: any ideas ?
> -------------------------------------------------------------------------
> tid tcb rstcb prty status vp-class name
> 2 7000000b162d9f0 0 1 IO Idle 10lio* lio vp 0
> 3 7000000b166a288 0 1 IO Idle 11pio* pio vp 0
> 4 7000000b1692288 0 1 IO Idle 12aio* aio vp 0
> 5 7000000b16ba288 0 1 IO Idle 13msc* msc vp 0
> 6 7000000b16f2528 7000000b0adc028 3 sleeping secs: 1 1cpu main_loop()
> 7 7000000b1638a50 0 1 running 14soc* soctcppoll
> 8 7000000b15236c0 0 2 sleeping forever 1cpu* soctcplst
> 9 7000000b1692830 0 2 sleeping forever 3cpu* soctcplst
> 10 7000000b16ba4e8 7000000b0adc858 1 sleeping secs: 1 1cpu flush_sub(0)
> 11 7000000b16ba7c0 7000000b0add088 1 sleeping secs: 1 1cpu flush_sub(1)
> 12 7000000b16baa98 7000000b0add8b8 1 sleeping secs: 1 1cpu flush_sub(2)
> 13 7000000b16bad70 7000000b0ade0e8 1 sleeping secs: 1 1cpu flush_sub(3)
> 14 7000000b1617300 0 3 running 3cpu* kaio
> 31 7000000b196a808 0 3 IO Idle 1cpu* kaio
> 37 7000000b1a7a388 7000000b0ade918 2 sleeping secs: 1 1cpu aslogflush
> 38 7000000b1a7a660 7000000b0adf148 1 sleeping secs: 125 1cpu btscanner_0
> 60 7000000b211c928 7000000b0ae09d8 3 sleeping secs: 1 1cpu* onmode_mon
> 61 7000000b211cb88 7000000b0ae01a8 3 sleeping secs: 1 1cpu periodic
> 62 7000000b257e028 0 3 IO Idle 4cpu* kaio
> 67 7000000b23ec418 7000000b0ae1a38 1 sleeping secs: 10 1cpu dbScheduler
> 69 7000000b2337028 7000000b0ae1208 1 sleeping forever 3cpu dbWorker1
> 70 7000000b2373568 7000000b0ae2268 1 sleeping forever 1cpu dbWorker2
> 73 7000000b21c5148 0 3 IO Idle 6cpu* kaio
> 76 7000000b21c55e8 0 3 IO Idle 7cpu* kaio
> 77 7000000b21c5ad8 7000000b0adf978 1 cond wait bp_cond 1cpu bf_priosweep()
> 78 7000000b22131e8 0 3 IO Idle 5cpu* kaio
> 87 7000000b5fd5550 0 3 IO Idle 9cpu* kaio
> 93 7000000b5fd5bc8 0 3 IO Idle 8cpu* kaio
> * 129 7000000b241a930 7000000b0ae3af8 1 IO Wait 3cpu ontape*
>
> IBM Informix Dynamic Server Version 11.50.FC5 -- On-Line -- Up 02:45:14 --
> 3142096 Kbytes
>
> Stack for thread: 129 ontape
> base: 0x07000000b603d000
>
> len: 135168
>
> pc: 0x00000001000429b0
>
> tos: 0x07000000b605a3b0
> state: sleeping
>
> vp: 3
>
> 0x00000001000429b0 (oninit)yield_processor_mvp
> 0x000000010004d400 (oninit)mt_yield
> 0x00000001000d1798 (oninit)mt_aio_wait
> 0x00000001000d1cb0 (oninit)mt_aio_start
> 0x00000001001e8268 (oninit)chunkio_int
> 0x00000001001e5ea8 (oninit)chunkio
> 0x00000001001ea52c (oninit)physio
> 0x00000001001ef024 (oninit)buffget
> 0x00000001001978c0 (oninit)pthdrgetx
> 0x000000010019cf80 (oninit)ptalloc
> 0x0000000100348664 (oninit)nxtpartp
> 0x0000000100345898 (oninit)prptnhdr
> 0x000000010033e064 (oninit)pstread
> 0x0000000100327288 (oninit)pst_rsread
> 0x00000001003306e8 (oninit)rsread
> 0x00000001004500fc (oninit)fmread
> 0x00000001007e811c (oninit)readseq
> 0x00000001007e883c (oninit)gettupl
> 0x00000001007ebc78 (oninit)scan_next
> 0x000000010089d57c (oninit)hjoin_open
> 0x0000000100bf41d0 (oninit)group_open
> 0x0000000100551718 (oninit)prepselect
> 0x0000000100458130 (oninit)excommand
> 0x000000010041c464 (oninit)sq_exselect
> 0x00000001002187a0 (oninit)sqmain
> 0x0000000100578b50 (oninit)listen_verify
> 0x0000000100577294 (oninit)spawn_thread
> 0x0000000100d0f93c (oninit)startup
>
> tid name rstcb flags curstk status
> 129 ontape 7000000b0ae3af8 Y--PR-M 12720 cond wait pt_448a8d -
>
> Memory pools count 2
> name class addr totalsize freesize #allocfrag #freefrag
> 92 V 7000000b2307040 229376 19480 293 27
> 92*O0 V 7000000b5fe9040 4096 808 1 1
>
> name free used name free used
> overhead 0 6576 mtmisc 0 144
> scb 0 144 opentable 0 7752
> filetable 0 1936 ru 0 600
> log 0 16536 temprec 0 2208
> keys 0 208 ralloc 0 128072
> gentcb 0 1584 ostcb 0 3400
> sort 0 104 sqscb 0 21696
> sql 0 72 hashfiletab 0 552
> osenv 0 3376 buft_buffer 0 4216
> sqtcb 0 10760 fragman 0 776
> shmblklist 0 704 udr 0 1768
>
> sqscb info
> scb sqscb optofc pdqpriority sqlstats optcompind directives
> 7000000b24e9110 7000000b274c028 0 0 0 0 1
>
> Sess SQL Current Iso Lock SQL ISAM F.E.
> Id Stmt type Database Lvl Mode ERR ERR Vers Explain
> 92 SELECT sysmaster RR Wait 300 0 0 9.24 Off
>
> Current SQL statement :
>
> select ( sum ( npused ) ) from sysdbspaces as D , sysptnhdr as P where D
>
> .. dbsnum = TRUNC ( P . partnum/ 1048576 ) and name = ?
>
> Host variables :
>
> address type flags value
>
> -----------------------------------------
>
> 0x07000000b5a2d268 CHAR 0x000 db11_13trnr
>
> Last parsed SQL statement :
>
> select ( sum ( npused ) ) from sysdbspaces as D , sysptnhdr as P where D
>
> .. dbsnum = TRUNC ( P . partnum/ 1048576 ) and name = ?
>
> mpm13trnr_prodappl(ifx/ifx) /tmp> more sqexplain.out
>
> QUERY: (OPTIMIZATION TIMESTAMP: 02-22-2011 13:58:12)
> ------
> select ( sum ( npused ) ) from sysdbspaces as D , sysptnhdr as P where
> D.dbsnum = TRUNC ( P.partnum/1048576 ) and name = "de07_13trnr"
>
> Estimated Cost: 30
> Estimated # of Rows Returned: 1
>
> 1) ifx.d: INDEX PATH
>
> Filters: ifx.d.name = 'de07_13trnr'
>
> (1) Index Name: informix.sysdbstab_dbsnum
>
> Index Keys: dbsnum
>
> Lower Index Filter: ifx.d.dbsnum> 0
>
> 2) ifx.p: SEQUENTIAL SCAN
>
> DYNAMIC HASH JOIN
>
> Dynamic Hash Filters: ifx.d.dbsnum = trunc(ifx.p.partnum / 1048576 )
>
> UDRs in query:
> --------------
>
> UDR id : 386
>
> UDR name: bitval
>
> UDR id : 386
>
> UDR name: bitval
>
> UDR id : 386
>
> UDR name: bitval
>
> UDR id : 386
>
> UDR name: bitval
>
> *Khaled Bentebal
>
> Email: khaled.bentebal@consult-ix.fr*
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--001517503b08b7dfb8049cfbf9db

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