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What is buffer in BUFFER POOL?

 
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dejunzhu

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PostPosted: Wed Jun 22, 2011 7:28 am    Post subject: What is buffer in BUFFER POOL?
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I'm quite familiar withe the concept "BUFFER POOL" in DB2, but how about Buffer?
from the name , I understand that BUFFER POOL is a place where a lot of buffer reside.

I searched the DB2 manuals, but all are about BUFFER POOL, no specification to the concept: buffer.

So, would you please give me a hint on this? thanks.
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enrico-sorichetti

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PostPosted: Wed Jun 22, 2011 11:43 am    Post subject: Reply to: What is buffer in BUFFER POOL?
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how in heaven can You say that You are familiar with BUFFER POOL when You seem to ignore the elementary concept of buffer icon_eek.gif

what happened when You googled for buffer or buffer computer science

no reason for us to retype what can be found with no effort in computer science literature
icon_cool.gif
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GuyC

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PostPosted: Wed Jun 22, 2011 12:10 pm    Post subject:
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isn't buffer a cow-like animal ?
or is it the thing made from milk which you use to bake stuff in ?
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enrico-sorichetti

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PostPosted: Wed Jun 22, 2011 3:56 pm    Post subject: Reply to: What is buffer in BUFFER POOL?
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the only time i heard buffer used for a dairy derivative
was when somebody asked for it with the mouth stuffed with sausages and bacon icon_biggrin.gif
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Bill Woodger

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PostPosted: Wed Jun 22, 2011 5:11 pm    Post subject: Reply to: What is buffer in BUFFER POOL?
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I thought there was milk from a "reduced-calorie buffer" used for making Mozarella?
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Robert Sample

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PostPosted: Wed Jun 22, 2011 6:33 pm    Post subject:
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Quote:
I'm quite familiar withe the concept "BUFFER POOL" in DB2, but how about Buffer?
Why do we not have a facepalm emoticon?

How can anyone be familiar with buffer pools but not know about buffers? It's like saying you are familiar with transportation but not know what a car is.
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Bill Woodger

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PostPosted: Wed Jun 22, 2011 6:39 pm    Post subject:
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Or Car Pools, and don't know what a Car is?

I like the sort of "Buffer Neighbourhood" definition. Lounging on the front steps in the summer, admiring the record-areas in their skimpy summer dresses... whoa, cold shower please.

Edit, if we're getting really off-topic. Another one off to FAQ (or CAQ).

Thomas the Tank engine has buffers. You also have buffers at the end of railway tracks. Sometimes Thomas, or the other engines, run into the buffers, which they would hit with their buffers. I don't think it has anything to do with pools.
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PeterHolland

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PostPosted: Wed Jun 22, 2011 6:39 pm    Post subject:
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A child can act as a buffer between its parents. So if there is more than 1 child we talk about a buffer pool.
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Akatsukami

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PostPosted: Wed Jun 22, 2011 10:48 pm    Post subject:
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Buffer is a high school cheerleader who learns that she is a Slayer, a chosen one gifted with the strength and skills to fight the forces of evil, and who carries out her destiny in...

Oops, that's Buffy. Never mind.
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dick scherrer

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PostPosted: Thu Jun 23, 2011 2:32 am    Post subject:
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Possibly a reference to the Pattern Buffer (rather important part of the Transporter - Beam me up / Energize)
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dejunzhu

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PostPosted: Thu Jun 23, 2011 2:32 pm    Post subject:
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From some articles, I can see buffer can be counted,
i.e. "10000 buffers in BP0",

so, how many allocation is needed for a buffer?
can buffer be caculated by "KB" or "MB" or cylinder/track?

Still, can you please give me some material on this concept for z/OS? thanks.
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Robert Sample

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PostPosted: Thu Jun 23, 2011 2:56 pm    Post subject:
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Quote:
so, how many allocation is needed for a buffer?
can buffer be caculated by "KB" or "MB" or cylinder/track?
The answer to your first question is, however many are needed. The answer to your second question is no -- one buffer represents the bytes required to read one physical block from the tape / disk / whatever into memory. How many bytes is that? If the block size is 4096 then the answer is 4096. If the block size is 32760 then the answer is 32760. Typically, buffer allocations are in terms of the number of buffers and not KB or MB or tracks or cylinders.

How many buffers are needed? That depends upon the file type, the access characteristics (sequential, random, skip sequential), and so forth. There is no single answer to the question. If there are not enough buffers, the processing is slowed down since the system is having to wait for data to move from the external media to memory. If there are too many buffers, the system uses resources to manage them and processing again suffers. QSAM (sequential) files default to 5 buffers while VSAM KSDS files default to 2 data and 1 index buffer. Neither default is anywhere near enough, generally.
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Anuj Dhawan

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PostPosted: Thu Jun 23, 2011 3:29 pm    Post subject:
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Buffer is an area of storage into which data is read or from which it is written. Typically, buffers are used only for temporary storage.

With respect to DB2:

    • 4-KB page buffer pools are named BP0 through BP49
    • 8-KB page buffer pools are named BP8K0 through BP8K9
    • 16-KB page buffer pools are named BP16K0 through BP16K9
    • 32-KB page buffer pools are named BP32K through BP32K9

This link might be of your interest too: http://www.ibm.com/developerworks/data/library/techarticle/0212wieser/#bufferpools
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dejunzhu

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PostPosted: Thu Jun 23, 2011 3:33 pm    Post subject:
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so, how do I know the buffer quantity is enough or not?
That is, how to determine the quantity of buffer for a particular buffer pool, e.g. BP0?
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Anuj Dhawan

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PostPosted: Thu Jun 23, 2011 3:43 pm    Post subject:
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If you browse through the link, I've linked to in my previous post, you'll find these direct answers:

http://www.ibm.com/developerworks/data/library/techarticle/0212wieser/#bufferpools

http://www.ibm.com/developerworks/data/library/techarticle/0212wieser/#performanceimplications
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enrico-sorichetti

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PostPosted: Thu Jun 23, 2011 6:59 pm    Post subject: Reply to: What is buffer in BUFFER POOL?
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a good place to start for the basics concepts that You need to get acquainted with is here
http://www.redbooks.ibm.com/abstracts/sg246366.html?Open

and here
http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/DGT2DI30/CCONTENTS?SHELF=DGT2BK81&DN=SC26-7397-03&DT=20080509081751

and here
http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/DGT2D470/CCONTENTS?SHELF=DGT2BK81&DN=SC26-7410-08&DT=20080602122917

after that for more advanced and detailed reading

search the IBM redbooks collection for the series
ABC of zOS System programming
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