Sybase 11.0.3 - How to compute memory usage 
Author Message
 Sybase 11.0.3 - How to compute memory usage

Hi all,

I'm having trouble working out how much memory is available to the database
server is actually available for data cache.  Working through the Sybase
"Performance and Tuning Guide" I get one answer, which I am not sure if it
is correct, because there does not seem to be a difinitive worksheet of all
the variables involved.

Some of the figures are best guesstimates - like the size of the static
data.  The P&T guide gives a range between about 2M and 3.5M.  Looking at
the Sybase log file for the server startup information, it quite gives a
different figure.

Below is a work sheet of my calculations (best viewed in a fixed font such
as courier).  We are using Sybase 11.0.3 on HP-UX 10.20, with about 300
users at peak times.

Any pointers on how to compute the actual memory usage would be good,
because we can then configure how much cache is used for data, how much for
procs and do we have enough for either to get suitable hit rates etc.

Thanks
Paul Morris
---

Item                          Number       Size      Amount     Total

CACHE USED AS RECORDED IN SYBASE.LOG
=======================================================================
PROCEDURE CACHE USAGE
proc buffers allocated         7,053         76     536,028
blocks left for proc header    7,107      2,048  14,555,136  15,091,164

DATA CACHE
Memory allocated for data cache    1 13,406,000  13,406,000  13,406,000

Total data and procedure cache used/configured               28,497,164

CACHE AND MEMORY USAGE CALCULATED
=======================================================================
ADD MEMORY
Memory Configured              40000      2,048  81,920,000  81,920,000

LESS CORE
Sybase Kernel                      1  4,856,000  4,856,000
Static Data                        1  3,000,000  3,000,000    7,856,000

LESS CONFIGURED ITEMS
number of open databases          12     17,000    204,000
number of locks                 5000         32    160,000
number of devices                 10        512      5,120
device stack                      10     34,000    340,000
number of extent i/o buffers       0         16          0      709,120

LESS ACTIVE USER CONNECTIONS
User Connections network overhead300     2,048     614,400
stack size                       300    34,000  10,200,000
stack guard size                 300     4,096   1,228,800
task stack overhead (NT4.0)      300         0           0   12,043,200

LESS Configured User Connections
user log cache size              500     2,048   1,024,000    1,024,000

GIVES Total memory for data and procedure cache              60,287,680

LESS
% of cache for procedure cache              50%              30,143,840

GIVES
Available data cache                                         30,143,840

--
Software Development Solutions
Innovus Ltd
Wellington, NZ
--
The views expressed are those of the author, not necessarily of Innovus
Limited.



Sat, 11 Aug 2001 03:00:00 GMT
 
 [ 3 post ] 

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