Shulou(Shulou.com)06/01 Report--

Direct path read

1. Principle:

This wait event occurs when the session reads the data block directly into the PGA, rather than the SGA, and the read data is usually private to the session, so it doesn't need to be put into the SGA as shared data, because it doesn't make sense. This data usually comes from temporary data, such as the sorted data of SQL in a session, the data generated during parallel execution, and the sorted data generated by Hash Join,merge join, because these data are only meaningful to the SQL operation of the current session, so they do not need to be put in the SGA.

two。 Cause:

When the direct path read wait event occurs, it means that a large amount of temporary data is generated on the disk, such as sorting, parallel execution, and so on. Or it means that there is not enough free space in PGA.

3. Measures:

One direction is to increase the PGA and other means, and the other is to reduce the amount of IO read or to determine whether to read through the buffer is more efficient.

Direct path write

1. Cause of occurrence:

This happens when oracle writes data directly from PGA to data files or temporary files, which can bypass SGA. It is most common in disk sorting. In this case, you should find the data file that operates most frequently (if it is sorting, it is likely to be a temporary file) and spread the load.

two。 Measure

Reduce the size of IO writes.

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