Assuming you are asking about the "index hint" feature common in many databases, PostgreSQL does not provide such a feature. This is an intentional decision made by the PostgreSQL team. A good overview of why and what you can do can be found here. The basic reason is that this is a performance optimization method that tends to cause more problems when the data changes, and PostgreSQL's optimizer can re-evaluate the plan based on statistics. In other words, what might be a good query plan today may not be a good query plan all the time, and index hints force a specific query plan.
As a very crude tool, for testing purposes, you can use the enable_seqscan and enable_indexscan parameters. See:
These are not intended for sustained production use. If you encounter problems with query plan selection, you should review the documentation for tracking query performance issues. Don't just set the enable_ parameter and leave.
Unless you have a very good reason to use an index, Postgres will probably make the right choice. why?
For small tables, sequential scanning is faster.
Postgres does not use indexes when the data types do not match, you may need to include appropriate conversions.
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Assuming you are asking about the "index hint" feature common in many databases, PostgreSQL does not provide such a feature. This is an intentional decision made by the PostgreSQL team. A good overview of why and what you can do can be found here. The basic reason is that this is a performance optimization method that tends to cause more problems when the data changes, and PostgreSQL's optimizer can re-evaluate the plan based on statistics. In other words, what might be a good query plan today may not be a good query plan all the time, and index hints force a specific query plan.
As a very crude tool, for testing purposes, you can use the
enable_seqscanandenable_indexscanparameters. See:enable_ParametersThese are not intended for sustained production use. If you encounter problems with query plan selection, you should review the documentation for tracking query performance issues. Don't just set the
enable_parameter and leave.Unless you have a very good reason to use an index, Postgres will probably make the right choice. why?
Also see this old newsgroup post.