Db2 LUW 11.1 LOB storage and I/O Question

Joe Geller

Db2 LUW 11.1 LOB storage and I/O Question

We have a LOB column that has a row that has a length of 500K.  The LOBS are stored in their own tablespace which has a pagesize of 32K.  After a Select of the column, the package cache is showing direct_reads of 1034.  If Db2 read a page with each read there should only be about 16 reads.  So obviously that is not what is happening.

Does anyone know how the LOB data is read or why there would be over 1000 direct reads?

Joe

Daniel Luksetich

Db2 LUW 11.1 LOB storage and I/O Question
(in response to Joe Geller)
Joe,

I believe all LOB data access results in direct reads, which is why I also deploy LOBs less than the longest available varchar for bit data as such so that I get buffered access. As far as the number of direct reads maybe it has something to do with the organization of the LOBs.

Dan



Daniel L Luksetich

DanL Database Consulting



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From: Joe Geller <[login to unmask email]>
Sent: Wednesday, June 13, 2018 9:19 AM
To: [login to unmask email]
Subject: [DB2-L] - Db2 LUW 11.1 LOB storage and I/O Question



We have a LOB column that has a row that has a length of 500K. The LOBS are stored in their own tablespace which has a pagesize of 32K. After a Select of the column, the package cache is showing direct_reads of 1034. If Db2 read a page with each read there should only be about 16 reads. So obviously that is not what is happening.

Does anyone know how the LOB data is read or why there would be over 1000 direct reads?

Joe



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