co-relation between DB2 PAGE and z/OS PAGE

Tushar Jha

co-relation between DB2 PAGE and z/OS PAGE

Esteemed Experts,

I have a question which might be very basic in nature.I have searched the net ( not extensively ) , but have not got any answers.

How are DB2 PAGES related to z/OS PAGES,FRAMES,SLOTS?

DB2 internally stores tablespaces and indexes in PAGEs of different sizes,  

In z/OS , A block of central storage is called a FRAME, a block of auxiliary storage (DASD) is called a SLOT, and a block of virtual storage is called a PAGE.So, PAGEs in z/OS are there to support virtual addressing.

 

  • When a DB2 PAGE is first brought in from DASD , it is brought into its designated Buffer Pool which is allocated inside the DBM1 address space of DB2, all of this obviously is happening inside z/OS.So, when the page is brought into buffer pool, where does z/OS ( or to be more precise its PAGING, virtual addressing ) comes into place. And when the DB2 PAGE is brought into buffer pool, is that really a z/OS PAGE or a portion of z/OS PAGE. As far as I know, z/OS only supports 4KB and 1MB PAGE sizes  ( will be happy to stand corrected ). DB2 has PAGE sizes of 4KB, 8KB, 16KB and 32KB. So, how does DB2 PAGE fit into z/OS page.

              Is DB2 doing this behind the scenes or there is no relation at all.

 

  • Also, how does this work, when DB2 PAGEs are written back to DASD from bufferpool.

 

  • How does DB2 PAGE relate to SLOTS ( block of z/OS storage on DASD ) since PAGES in DB2 are called PAGES even when they are in DASD

 

  • Does z/OS paging play any role in the way DB2 divides its tablespace/index into PAGEs

 

This probably doesn’t affect my day to day work, and some of this probably has more to do with z/OS intricacies.

 I would be very grateful, if you can shed some insights on this or point me to any documentation which would help me understand this.

 

Thanks in advance,

Tushar Jha.

Philip Sevetson

co-relation between DB2 PAGE and z/OS PAGE
(in response to Tushar Jha)
**please note my email address change**
Tushar,

The short answer is that there isn’t much connection between z/OS Pages and DB2 pages. A DB2 page is an image of a data page from a VSAM LDS which is (part of) the DB2 pageset. It may have updates written to it, and those updates may or may not yet be reflected to the underlying LDS.

A DB2 Page is read into, or “externalized” from (written back to its underlying dataset on DASD), a DB2 Bufferpool (and potentially GroupBufferPool, for parallel-sysplex installations).

A DB2 Bufferpool is one or more z/OS PAGEs, with page size determined (I think) by DB2 subsystem parameters. DB2 Bufferpools can be paged, or can be un-page-able, again depending on DB2 subsystem parameters, but are always (a) z/OS Page(s).

So: A DB2 Page contains data, and is transiently in a z/OS Page. But there isn’t any connection between them which isn’t mediated by the DB2 subsystem (Bufferpool Manager).

Hope that helps, and of course, I’d welcome corrections from other List-ers on matters of fact in the above.

Philip Sevetson
Computer Systems Manager
5 Manhattan West (33rd St at 10th Ave)
New York, NY 10001-2632
212-857-1688 w
917-991-7052 c
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From: Tushar Jha [mailto:[login to unmask email]
Sent: Monday, September 25, 2017 11:41 AM
To: [login to unmask email]
Subject: [DB2-L] - co-relation between DB2 PAGE and z/OS PAGE


Esteemed Experts,

I have a question which might be very basic in nature.I have searched the net ( not extensively ) , but have not got any answers.

How are DB2 PAGES related to z/OS PAGES,FRAMES,SLOTS?

DB2 internally stores tablespaces and indexes in PAGEs of different sizes,

In z/OS , A block of central storage is called a FRAME, a block of auxiliary storage (DASD) is called a SLOT, and a block of virtual storage is called a PAGE.So, PAGEs in z/OS are there to support virtual addressing.



* When a DB2 PAGE is first brought in from DASD , it is brought into its designated Buffer Pool which is allocated inside the DBM1 address space of DB2, all of this obviously is happening inside z/OS.So, when the page is brought into buffer pool, where does z/OS ( or to be more precise its PAGING, virtual addressing ) comes into place. And when the DB2 PAGE is brought into buffer pool, is that really a z/OS PAGE or a portion of z/OS PAGE. As far as I know, z/OS only supports 4KB and 1MB PAGE sizes ( will be happy to stand corrected ). DB2 has PAGE sizes of 4KB, 8KB, 16KB and 32KB. So, how does DB2 PAGE fit into z/OS page.

Is DB2 doing this behind the scenes or there is no relation at all.



* Also, how does this work, when DB2 PAGEs are written back to DASD from bufferpool.



* How does DB2 PAGE relate to SLOTS ( block of z/OS storage on DASD ) since PAGES in DB2 are called PAGES even when they are in DASD



* Does z/OS paging play any role in the way DB2 divides its tablespace/index into PAGEs



This probably doesn’t affect my day to day work, and some of this probably has more to do with z/OS intricacies.

I would be very grateful, if you can shed some insights on this or point me to any documentation which would help me understand this.



Thanks in advance,

Tushar Jha.

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