内容简介：This tells us that Postgres would do aWe have documented many of the operations and field definitions you’re likely to come across while using EXPLAIN, along with performance advice and links to further learning resources.For advice in the context of your
EXPLAIN is the command used to request the execution plan for a query. It is incredibly useful when you want to explore what is going on, and see if there could be a more efficient way.
PostgreSQL does an amazing job populating query plans with useful information, but reading and understanding them can be tricky.
Here is a simple example:
Query ---------- explain select * from t order by c; Query plan ---------- Sort (cost=813.32..837.48 rows=9664 width=32) Sort Key: c -> Seq Scan on t (cost=0.00..173.64 rows=9664 width=32)
This tells us that Postgres would do a sequential scan of our table “t”, then a sort by column “c”. The numbers tell us the startup cost , the total cost , the plan rows , and the plan width at each stage.
We have documented many of the operations and field definitions you’re likely to come across while using EXPLAIN, along with performance advice and links to further learning resources.
For advice in the context of your query plans, check out our product pgMustard .
Main scan operations
Main join operations
All operations
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CTE Scan
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Named Tuplestore Scan
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Sample Scan
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TableFunc Scan
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TID Scan
EXPLAIN parameters
Official docs
Further reading
Last updated: June 2020, PostgreSQL 12
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