brbackup/backint consumes all my RAM on Linux

[Former Member]

I am investigating the disappearnce of RAM in my Linux hosted SAP ECC6 Development System on SLES10 and Oracle 10.2.0.4. The box is hosted on a VM but as this problem only happens when the backup is ssheduled I have ruled out VM as the cause for the time being.

The box has 24GB or RAM allocated.

After starting Oracle just over 1GB is used.

After starting R3 just over 2.5GB is used.

During the normal operations the used increases to 7GB leaving 17GB Free.

Brbackup starts at 09:00 and with no other large processes running suddenly Free RAM drops off to 112MB. When the backup completes the free RAM remains at 118MB. Why do I think that the backup may be the cause? Because I restarted the server just over a week ago, and got the same dropoff or RAM at the same time on the same day. (being a DEV system I only do a full backup  a couple of days a week).

If you have any ideas of how to fix this issue please respond.

[Former Member · Accepted solution]

I have a fix, but am not yet sure as to the longevity of this fix.

as root I ran the following:-

echo "3" > /proc/sys/vm/drop_caches

This gave back all the taken cache to system. RAM now has 19GB free.

The command was ran whilst the system was up, it had no negative impacts on the application.

[Former Member · Accepted solution]

FYI:- Having monitored the situation for a week, the RAM was again consumed by my backups and was not released after the end of the backup. I set the command  to drop the caches at a time approximately after the end of the backups using crontab and that has fixed the issue. This fix is suitable for our Dev systems but would require a better solution for a productive instance.

[Former Member]

Hello Mark,

in order to avoid that all the available physical RAM is consumed on your system by the file system cache during backups I would recommend to check if it is possible to configure your backup software to use DirectIO. With DirectIO enabled all data written by the backup software would go directly to the storage without being cached in the file system cache by the OS first thus avoiding that the RAM gets filed by the file system cache during backups.

Regards,

Frank Danapfel

[former_member360066]

Your RAM isn't really "consumed" in the sense that it's lost for other things. It's just, that Linux has cached the data in it's "file system cache". As soon as some applications need memory, Linux will free it automatically.

So, in general there is nothing to worry about. That's just normal Linux behaviour.

[Former Member]

Thanks for your reply Helge, I have read this on some forums but in my case I think it is incorrect. Before the RAM disappears I have no problems with performance and no visible paging in ST06. However when ST06 reports only 112MB free I then also start to see very large amounts of page occurring as well as the development team complaining about performance (which they didnt before).

[former_member360066]

It's still correct what I said - what you see that the Linux kernel pages out memory (and thus it may become slow for users) is due to how the Linux kernel decides when and which pages it should swap out in favour to be able to increase the file system cache during your backup.

I would suggest you take a look at the SAP notes:

1382721 - Linux: Interpreting the output of the command 'free', and

1557506 - Linux paging improvements

[Former Member]

I do like that answer Helge. I experienced a very similar problem in a windows system with large page reported in ST06 during backups and brarchives even though there was free RAM.

Best regards, Yours Mark.

[Reagan]

Good Day Mark

Have you tried updating the BRTools and install the latest version of the TDP software ?

Regards

RB

[Former Member]

Thanks RB, I shall try that.

Yours Mark