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direct path read

Short Description

During Direct Path operations the data is asynchronously read from the database files. At some stage the session needs to make sure that all outstanding asynchronous I/O have been completed to disk. This can also happen if during a direct read no more slots are available to store outstanding load requests (a load request could consist of multiple I/Os).

Detailed Description​

You will see direct path read and direct path read temp waits when:

Sorts are too large for memory and have been written to disk.

When parallel execution servers are scanning for data

When the server process is processing buffers faster than the I/O system can return them.

Direct path reads load data from disk directly into your processes private memory - the Program Global Area (PGA) rather than the shared memory normally associated with database reads. Asynchronous I/O will be used if possible.

How to reduce this wait​

Use the tuning script from oracle-base.com and look in the 'Disk Sorts' section to see if you have excessive sorts to disk occurring. Tune the SQL to reduce sorting, and consider adjusting the PGA_AGGREGATE_SIZE parameter to allow more sorting in memory.

If you have a decision support system running parallel queries, this will be the mechanism used to return data.

Oracle Performance Tuning Guide - direct path read and direct path read temp

Oracle Reference - PGA_AGGREGATE_TARGET

Tuning script from oracle-base.com

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