Subject Re: [firebird-support] Re: Issue with Database Cache Size on FB 3.0
Author
Post date 2016-06-01T14:00:22Z
Hi Dmitry
I am progressing with solving this one, the first issue was related with a config variable reserving most of the ram upfront, hence there was no ram available for the DB cache. The second issue was misinterpreting what the following meant:
 
# File system cache size
# Note that the lowest number presently supported is 10%, and the highest number
# is 95%; numbers outside these limits will be set to the default of 30%.
 
First interpretation on the above was the variable must be between 0 and 1, as 50% in math is usually written as 0.5, but then the following made it confusing:
# Type: integer, measured in % of total physical RAM
 
Where it says "integer" it complicated things, as it would not make sense to have a percentage forced to be integer, as there would be no way to represent 40.5% for instance. So I assume the value is an integer because it is representing bytes, and bytes cannot have decimals.
 
Anyways, as I play along with different configurations I am finding the FB 3 server VERY responsive interms of multiusers, I am glad the SMP efforts are showing very interesting performance, so congrats to all the development team!!!!!!
 
As a test I am using IBexpert to compare the data between the FB 2.54 DB and the 3.0, it is a 80 GB database, and at the same time I am loading users on the FB 3 database, and the performance is almost as good as running without any other parallel process, so I am very impressed.
 
 
Cheers
Fabian
 

 
----- Original Message -----
Sent: Wednesday, June 01, 2016 3:49 PM
Subject: [firebird-support] Re: Issue with Database Cache Size on FB 3.0

01.06.2016 04:16, Fabian Ernesto Chocron wrote:
>
> We are having trouble setting up the database cache size on FB 3.0
> running on Windows 2008 R2 64 bits with 32 GB ram.
>
> The problem we have is we cannot get the server to allocate the ram for
> the cache as we intend. With FB 2.54 we had the DB cache set very high,
> close to 1 GB per database, all running in RAM memory. With FB 3.0 we
> read it can allocate much more RAM to the cache, but it appears the
> server is allocating very small amount of Ram when the first user
> connects to the DB, and as we connect more users to the DB the ram
> consumption increases slowly.

What memory counters do you look at? Virtual (reserved) memory usage
should grow high with the first connect, physical (committed) memory
usage should grow together with your load, while pages are being read
from disk.

> On firebird.conf
>
> FileSystemCacheThreshold = 0
> FileSystemCacheSize = 17179869184 (this is 16 GB - the server has 32 GB
> ram.)

These changes conflict with each other. You disable filesystem cache
with the first line and still want to use 16GB with the second line.

> On databases.conf
>
> MyTestDB = c:\Temp\MyDb.fdb
> {
> DefaultDbCachePages = 458752
> }

First of all, I'd suggest to reset FileSystemCacheSize back to zero and
set FileSystemCacheThreshold to something higher than 458752 pages (e.g.
500000). Then re-test your memory usage and only then start tweaking the
filesystem cache.

BTW, don't you occasionally have page cache override at the database
level? What is gstat -h output?


Dmitry




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