From f941d033296eb99eeac60f22fc70938893bf7a30 Mon Sep 17 00:00:00 2001 From: Simon Riggs Date: Fri, 15 May 2015 21:54:18 -0400 Subject: [PATCH] Add docs for tablesample system_time() --- doc/src/sgml/tsm-system-time.sgml | 51 +++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 doc/src/sgml/tsm-system-time.sgml diff --git a/doc/src/sgml/tsm-system-time.sgml b/doc/src/sgml/tsm-system-time.sgml new file mode 100644 index 0000000000..2343ab16d4 --- /dev/null +++ b/doc/src/sgml/tsm-system-time.sgml @@ -0,0 +1,51 @@ + + + + tsm_system_time + + + tsm_system_time + + + + 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. + + + + Examples + + + 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). + + + +