Troubleshooting

To troubleshoot a query, you can examine its EXPLAIN plan.

PostgreSQL's EXPLAIN feature allows users to understand the underlying query plan that PostgreSQL uses to execute a query. There are multiple ways that PostgreSQL can execute a query: for example, a query might be fulfilled using a slow sequence scan or a much more efficient index scan. The choice of plan depends on what indexes are created on the table, the statistics that PostgreSQL has about your data, and various planner settings. The EXPLAIN output let's you know which plan PostgreSQL is choosing for a particular query. PostgreSQL has a in-depth explanation of this feature.

To understand the query performance on a hypertable, we suggest first making sure that the planner statistics and table maintenance is up-to-date on the hypertable by running VACUUM ANALYZE <your-hypertable>;. Then, we suggest running the following version of EXPLAIN:

EXPLAIN (ANALYZE on, BUFFERS on) <original query>;

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If you suspect that your performance issues are due to slow IOs from disk, you can get even more information by enabling the track_io_timing variable with SET track_io_timing = 'on'; before running the above EXPLAIN.