PXA Buffer Swaps

[benoit-schmid]

Hello,

On our PRD ECC 6.04 system, we have swaps for the program buffer.

The abap/buffer size is set to 800 MB which I consider high,

as we only have 100 users and a Max reached em size of 1.5 GB for the week.

The hit rate of this buffer is 100%.

The following url (http://help.sap.com/saphelp_nw70/helpdata/en/bc/4a813b680c250fe10000000a114084/content.htm)

says "Increase the size of the buffer if the swap rate (the replacing of buffer objects) is very high, or if the hit rate is below the target threshold value".

1. What is a high swap rate?

I remember having read 10k swaps per day, but I did not succeed to find this on the SAP online help.

2. Is it true to say that compiled programs are never cleared from buffer,

except if new space is needed for new programs?

We have applied the latest SPS last week. After this a restart of sap has been performed.

Therefeore the buffers have been cleared.

3. Even so, can this swaping activity be due to the SPS and the compilations implied?

I think that new loads needs to be reloaded in pxa even if there is free space.

4. Am I right?

5. Can I find the biggest loads in this buffer?

I see the columns PXA Offset and Used in st02, but I do not know their exact meanings.

Thanks in advance for your answers.

[JPReyes · Accepted solution]

According to CCMS a high program buffer SWAP rate is 1000 times per minute. Read the details of the R3BufferProgramSwap MTE.

In my experience some swaping is not an issue, specially if you just runned SGEN when its actually logical that the system will report SWAPS.

Usually this buffer hold frequently used programs, in which most of them are standard so you can assume that some programs never leave the buffer because of their utilization, during a swap objects that were used the least recently are removed to accomodate new ones.

800000 is a good size for an abap buffer but if you are experiencing SWAP's and you are concerned about their impact on your system you can by all means raise the bar.

Regards, Juan

[benoit-schmid · Accepted solution]

Hello Juan,

By the ways my swap ccms for program is always green.

But my SpaceUsed is allways red because it stays at 100%.

From what I understand it has to stay to 100% as it is only emptied when a new object must be inserted.

Is it correct?

And what about my following questions

5. Can I find the biggest loads in this buffer?

I see the columns PXA Offset and Used in st02, but I do not know their exact meanings.

Thanks in advance for your answers.

[former_member189725 · Accepted solution]

PXA uses the Least recently used algorithm to displace objects out of the buffer .

Even if 100% is used , it should not worry you and since you have run SGEN the ABAP loads have filled up the buffer. The next time when you restart the application instance , you will see 800 MB too enough .

The Columns PXA offset , the point(measured in KB)  from which the buffered object occupies space. The first is 0 and then keep adding the size of the object to get the next offset.

The  Used is the number of times the object has been used while being in the buffer.

Regards

Ratnajit

[benoit-schmid · Accepted solution]

Hello,

Ratnajit Dey wrote:
Even if 100% is used , it should not worry you and since you have run SGEN the ABAP loads have filled up the buffer. The next time when you restart the application instance , you will see 800 MB too enough .

If having the buffer full is not a problem, why is the CCMS configured by SAP to be red above 98%?

Thanks in advance for your answer.

[former_member189725 · Accepted solution]

I have mentioned this as of now .. not for always as there is a valid reason for your PXA buffer to be filled since SGEN was run.

Also the PXA buffer experiences swaps for objects which is common.

And to be practical , putting a threshold of 100% really does not make sense.

Regards

Ratnajit

[benoit-schmid · Accepted solution]

Hello,

Ratnajit Dey wrote:
I have mentioned this as of now .. not for always as there is a valid reason for your PXA buffer to be filled since SGEN was run.

Is this buffer reset after a restart of SAP?

If yes, it should be almost empty just after starting sap.

Thanks in advance for your answer.

[benoit-schmid · Accepted solution]

Hello,

Ratnajit Dey wrote:
And to be practical , putting a threshold of 100% really does not make sense.

I fully agree with you.

But my point is that checking the buffer size in ccms does not make sense either.

Regards,

[former_member189725 · Accepted solution]

After a system restart or buffer reset , your buffer would be flushed so after that it should be fine with 800 MB of PXA buffer size.

Regards

Ratnajit

[former_member189725 · Accepted solution]

After a system restart or buffer reset , your buffer would be flushed so after that it should be fine with 800 MB of PXA buffer size.

Regards

Ratnajit

[benoit-schmid · Accepted solution]

Hello,

As my system was restarted last week end, after the sgen, it has been refilled in 3 days.

Therefore it is not due to sgen this time.

Regards,