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Cache sizes in ASE 16.0, SP03 PL01

Sep 20, 2017 at 04:41 AM

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Former Member

This relates to SAP note 2490727 - "cache size value changes during upgrade or downgrade" See: https://launchpad.support.sap.com/#/notes/2490727

We upgraded to SAP ASE 16.0, SP03, PL01 from ASE 16.0 SP01 running on AIX

[AIX oslevel 7100-04-04-1717]

Using the ASE cache wizard in sp_sysmon, it is now showing half the amount of cache "Run Size" as compared to before the upgrade to SP03 PL01
When I use DB Artisan, looking in "Data Caches", I see half the cache "Run" size too, which seems to agree with the aforementioned SAP note.
However, when running sp_cacheconfig and sp_helpcache in sql, it still reports the same cache size as was there before the upgrade.
The config file in ASE-16 folder in AIX still has the original cache size too.

What's going on with these cache sizes here, anyone else getting this too ?

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5 Answers

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Mark A Parsons Sep 25, 2017 at 08:34 PM
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The most likely explanation is that someone at SAP failed to update the sp_sysmon/cache(wizard) stored proc with the new logic for calculating cache size.

Someone at SAP forgot to change the calculation multiplier from 1024 to 2048 ... so with just half the necessary multiplier in use ... you're only seeing half the value in the resulting calculation.

Fixing this issue will require a) opening a ticket with SAP so they can make the code change and b) if you can't wait for the SAP-supplied fix then you can update the sp_sysmon/cache(wizard) stored proc yourself.

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Mark A Parsons Sep 22, 2017 at 01:37 PM
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NOTE: Not everyone on this forum has access (ie, a SAP support contract) to SAP notes, so if there's something of interest/importance in a note that you wish to reference then you should include that info directly in your post (assuming it doesn't break any SAP rules), otherwise a link to a SAP note is as good as a broken link.

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With ASE 16.0 SP02 PL06, a behind-the-scenes/under-the-covers change was made to sysconfigures.value to support maximum cache sizes of 4TB (increased from 2TB).

With previous ASE versions, sysconfigures.value represented the number of 1KB pages allocated for a cache, so any (cache-related) calculations would need to multiply sysconfigures.value by 1024 (1KB) to obtain the size of the cache.

Starting with ASE 16.0 SP02 PL06, sysconfigures.value now represents the number of 2KB pages allocated for a cache, so any (cache-related) calculations now need to multiply sysconfigures.value by 2048 (2KB) to obtain the size of the cache.

The variations you're seeing in cache sizing (actual vs half) would seem to indicate that the above change in multiplication factors was not rolled out successfully to the entire ASE codeline. I suggest you open a case with tech support so this issue can be fixed.

In the mean time you can either 'mentally' double the questionable value or fix/update the questionable piece of T-SQL in the corresponding system procs.

Reference:

ASE 16.0 SP02 PL06 - What's New [see Table 1: 16.0 SP02 PL06 Enhancements, entry #3 titled "Support for Cache Memory up to 4TB" ]

NOTE: Since some of the system procs appear to be reporting the correct cache sizes I'm going to assume that after the ASE binary upgrade you did run the installmaster script against the dataserver.

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As for why DBArtisan is showing the wrong cache size ... *shrug* ... I don't use DBArtisan so I can only guess at this point ...

a - DBArtisan calls a ASE-supplied system proc that has not been updated [would need SAP to update the system proc(s) accordingly]

or

b - DBArtisan has some hard-coded logic for calculating cache sizes (ie, doesn't know about the change in multiplication factor from 1024 to 2048) [would need to get the owners of DBArtisan to update their product ... if not already updated in a newer version of DBArtisan]

I'm guessing a little bit of MDA table analysis should help figure out which of the above explains DBArtisan's issue.

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Former Member Sep 25, 2017 at 08:15 PM
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Thanks for the reply Mark.

Yes, we used updatease and installmaster script installed successfully.

sp_version shows: 16.0 SP03 PL01/EBF 27405 SMP/P/powerpc/AIX 7.1.3.15/asecorona/2997/64-bit/OPT/Fri Jul 28 03:27:56 2017 as Complete.


If we leave DBArtisan aside, I'm curios why ASE cache wizard in sp_sysmon, is now showing half the amount of cache "Run Size" as compared to before the upgrade to SP03 PL01 yet when I check the cfg file it shows the original amount.

e.g: ASE cache wizard using EXEC sp_sysmon "00:10:00", 'cache wizard', '10' shows, 'xyz_data cache' as "Run Size : 25.00 Mb"

Whereas the config file says:

[Named Cache:xyz_data cache]
cache size = 51200K
cache status = mixed cache
cache replacement policy = strict LRU replacement
local cache partition number = 1

[2K I/O Buffer Pool]
pool size = DEFAULT
wash size = 6400 K
local async prefetch limit = 10

[16K I/O Buffer Pool]
pool size = 12288.0000k
wash size = 3200 K
local async prefetch limit = 10


The config file says it is 50mb (above) , sp_cacheconfig (config and run value are 50 Mb) and sp_helpcache (config and runsize is 50Mb), yet cache wizard is saying 25Mb.

Before the upgrade these figures all agreed with each other.

The question arising from this is how much memory are we really allocating to cache then and has anyone else experienced this ?

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Former Member Sep 25, 2017 at 10:39 PM
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Ah, that makes sense.

We upgraded 2 different ASE servers and the issue is on both, I checked the procs in sybsystemprocs db and they all have created dates for the same as the upgrade.

Will raise a ticket with SAP as this is not a show stopper for us ( not that keen to dive into their code :-) ).

Thanks,

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Former Member Sep 27, 2017 at 09:37 PM
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Anyone reading this later: I've logged an incident with SAP for this and they confirmed it is a bug and will be fixed in a later version. In the meantime use 'sp_cacheconfig' and 'sp_helpcache' for confirmation of sizing.

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