lots of Virtual portion memory with less used spac
Poster asked why `onstat -g seg` on IDS 9.21 showed many virtual-portion segments that were almost entirely empty, suspecting misconfiguration. Replies explained this is normal: when a big memory demand (e.g. a large query) arrives, IDS adds segments in SHMADD-sized chunks all at once, and when that memory is released the segments stay allocated but appear mostly free. The message log (onstat -m) confirms the burst of allocations. Suggested remedies: run `onmode -F` to drop fully unused segments (partly used ones won't be released), and raise SHMVIRTSIZE/SHMADD so enough memory is pre-allocated up front, within 32-bit limits.
Auto-generated by DrWatson from the posts below — may be imperfect; read the full thread.
An onstat -g seg gives following output. What is configured wrong or whats
going wrong on the system. Why is informix using few space in each memory
segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187
2630 1381386255 70f00000 45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
Art already explained how the segments appear.
Maybe you can consider the use of "onmode -F" to cleanup
The space and keep as few segments as possible.
Jacques
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
NADINE DIELTJENS
Sent: dinsdag 5 september 2006 15:02
To: ids@iiug.org
Subject: lots of Virtual portion memory with less used spac [7427]
An onstat -g seg gives following output. What is configured wrong or
whats
going wrong on the system. Why is informix using few space in each
memory
segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187
2630 1381386255 70f00000 45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
************************************************************************
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We do this regularly, but the existing segments won't be released.
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Lapeire, Jacques
Sent: dinsdag 5 september 2006 15:31
To: ids@iiug.org
Subject: RE: lots of Virtual portion memory with less u.... [7431]
Art already explained how the segments appear.
Maybe you can consider the use of "onmode -F" to cleanup The space and
keep as few segments as possible.
Jacques
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
NADINE DIELTJENS
Sent: dinsdag 5 september 2006 15:02
To: ids@iiug.org
Subject: lots of Virtual portion memory with less used spac [7427]
An onstat -g seg gives following output. What is configured wrong or
whats going wrong on the system. Why is informix using few space in each
memory segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187 2630 1381386255 70f00000
45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
************************************************************************
*******
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************************************************************************
*******
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Jacques,
It still is a open question for me , why he is using as lots of virtual
portions.
That informix takes a new when the existing ones don't have enough space
left is ok.
But why , is he taking new ones while in the existing ones has still
lots of space free ?
Thanks a lot already for your reaction.
-----Original Message-----
From: Lapeire, Jacques [mailto:jacques.lapeire@siemens.com]
Sent: dinsdag 5 september 2006 15:31
To: Dieltjens, Nadine
Subject: RE: lots of Virtual portion memory with less u.... [7431]
Art already explained how the segments appear.
Maybe you can consider the use of "onmode -F" to cleanup The space and
keep as few segments as possible.
Jacques
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
NADINE DIELTJENS
Sent: dinsdag 5 september 2006 15:02
To: ids@iiug.org
Subject: lots of Virtual portion memory with less used spac [7427]
An onstat -g seg gives following output. What is configured wrong or
whats going wrong on the system. Why is informix using few space in each
memory segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187 2630 1381386255 70f00000
45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
************************************************************************
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************************************************************************
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Look at the online message log (onstat -m & more/less the MSG file), I would
venture to guess that IDS allocated all or at least most of those additional
segments at the same time, one right after the other. This would be because
SHMADD is too small for a single segment to satisfy the required memory needs.
Once the needed space is freed it will show up as unused in the onstat -g seg
output. If you ran the onstat -g seg at the time the segments were allocated
you would have seen almost no unused space.
Art S. Kagel
----- Original Message -----
From: Nadine Dieltjens <ids@iiug.org>
At: 9/05 9:54:25
Jacques,
It still is a open question for me , why he is using as lots of virtual
portions.
That informix takes a new when the existing ones don't have enough space
left is ok.
But why , is he taking new ones while in the existing ones has still
lots of space free ?
Thanks a lot already for your reaction.
-----Original Message-----
From: Lapeire, Jacques [mailto:jacques.lapeire@siemens.com]
Sent: dinsdag 5 september 2006 15:31
To: Dieltjens, Nadine
Subject: RE: lots of Virtual portion memory with less u.... [7431]
Art already explained how the segments appear.
Maybe you can consider the use of "onmode -F" to cleanup The space and
keep as few segments as possible.
Jacques
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
NADINE DIELTJENS
Sent: dinsdag 5 september 2006 15:02
To: ids@iiug.org
Subject: lots of Virtual portion memory with less used spac [7427]
An onstat -g seg gives following output. What is configured wrong or
whats going wrong on the system. Why is informix using few space in each
memory segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187 2630 1381386255 70f00000
45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
************************************************************************
*******
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************************************************************************
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*******************************************************************************
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Hi,
Informix allocates as much shared memory as it needs (if there is not a
limit in onconfig).
The allocation is done in the portions you can set in onconfig.
In case there is a big query in need to have lots of shared memory, the db
will allocate some segments.
These will only be freed again if they are completely unused and you execute
the onmode -F command.
After executing this big query, the memory is freed internally, but not the
segments.
As a result, you will have some segments allocated which are partly used.
This is what your output shows.
In case your system needs more shared memory than 350MB (as in your listing)
for normal execution, it is better to pre-allocate a higher amount
initially.
Since you are using a 32 bit system, you can enhance the SHMSIZE up to about
800MB (i encountered this value once on 9.30). The maximum might be
different for 9.21 (rather old, and out of support).
Marcus
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of
Dieltjens, Nadine
Sent: Tuesday, September 05, 2006 3:48 PM
To: ids@iiug.org
Subject: RE: lots of Virtual portion memory with less u.... [7434]
Jacques,
It still is a open question for me , why he is using as lots of virtual
portions.
That informix takes a new when the existing ones don't have enough space
left is ok.
But why , is he taking new ones while in the existing ones has still lots of
space free ?
Thanks a lot already for your reaction.
-----Original Message-----
From: Lapeire, Jacques [mailto:jacques.lapeire@siemens.com]
Sent: dinsdag 5 september 2006 15:31
To: Dieltjens, Nadine
Subject: RE: lots of Virtual portion memory with less u.... [7431]
Art already explained how the segments appear.
Maybe you can consider the use of "onmode -F" to cleanup The space and keep
as few segments as possible.
Jacques
-----Original Message-----
From: ids-bounces@iiug.org [mailto:ids-bounces@iiug.org] On Behalf Of NADINE
DIELTJENS
Sent: dinsdag 5 september 2006 15:02
To: ids@iiug.org
Subject: lots of Virtual portion memory with less used spac [7427]
An onstat -g seg gives following output. What is configured wrong or whats
going wrong on the system. Why is informix using few space in each memory
segment ?
Informix Dynamic Server 2000 Version 9.21.UC3 -- On-Line -- Up 69 days
17:58:55 -- 1867776 Kbytes
Segment Summary:
id key addr size ovhd class blkused blkfree
102 1381386241 a000000 1168113664 250928 R 284996 188
107 1381386246 4fa00000 356515840 11480 V 37374 49666
2024 1381386248 64e00000 1048576 632 M 133 123
201 1381386249 64f00000 33554432 1624 V 7 8185
225 1381386250 66f00000 33554432 1624 V 20 8172
126 1381386251 68f00000 33554432 1624 V 9 8183
127 1381386252 6af00000 33554432 1624 V 6 8186
128 1381386253 6cf00000 33554432 1624 V 9 8183
129 1381386254 6ef00000 33554432 1624 V 5 8187 2630 1381386255 70f00000
45088768 1976 V 1 11007
731 1381386256 73a00000 45088768 1976 V 1 11007
432 1381386257 76500000 48234496 2072 V 1 11775
433 1381386258 79300000 48234496 2072 V 1 11775
Total: - - 1913651200 - - 322563 144637
************************************************************************
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************************************************************************
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