Understanding Buffer Pool Performance and Tuning in DB2 UDB v8.1
Understanding Buffer Pool Performance and Tuning in DB2 UDB v8.1
Understanding Buffer Pool Performance and Tuning in DB2 UDB v8.1
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Non-<strong>Buffer</strong>ed IO<br />
� The buffer pool is not ideal for all types of IO<br />
� Large object data types such as LONG VARCHAR,<br />
BLOB <strong>and</strong> CLOB are retrieved directly from disk<br />
us<strong>in</strong>g non-buffered (direct) IO<br />
� Keep<strong>in</strong>g large object pages out of the buffer pool<br />
helps <strong>DB2</strong> ma<strong>in</strong>ta<strong>in</strong> effective cach<strong>in</strong>g for small<br />
data types<br />
1 GB BLOB 1 GB BP Disk<br />
Without direct IO,<br />
large data types would<br />
force <strong>DB2</strong> to flush all<br />
resident pages to disk<br />
– ru<strong>in</strong><strong>in</strong>g the hit rate
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