PostgreSQL 9.5alpha1 Documentation | |||
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The tsm_system_time module provides the tablesample method SYSTEM_TIME, which can be used inside the TABLESAMPLE clause of a SELECT.
This tablesample method uses a linear probing algorithm to read sample of a table and uses time in milliseconds as limit (unlike the SYSTEM tablesample method which limits by percentage of a table). This gives you some control over the length of execution of your query.
Here is an example of selecting sample of a table with SYSTEM_TIME. First install the extension:
CREATE EXTENSION tsm_system_time;
Then you can use it in a SELECT command the same way as other tablesample methods:
SELECT * FROM my_table TABLESAMPLE SYSTEM_TIME(1000);
The above command will return as large a sample of my_table as it can read in 1 second (or less if it reads whole table faster).