Question

I have a scenario where I have a central server and a node. Both server and node are capable of running PostgreSQL but the storage space on the node is limited. The node collects data at a high speed and writes the data to its local DB.
The server needs to replicate the data from the node. I plan on accomplishing this with Slony-I or Bucardo.
The node needs to be able to delete all records from its tables at a set interval in order to minimize disk space used. Should I use pgAgent with a job consisting of a script like

DELETE FROM tablex, tabley, tablez;

where the actual batch file to run the script would be something like

@echo off
C:\Progra~1\PostgreSQL\9.1\bin\psql -d database -h localhost -p 5432 -U postgres -f C:\deleteFrom.sql

?

I’m just looking for opinions if this is the best way to accomplish this task or if anyone knows of a more efficient way to pull data from a remote DB and clear that remote DB to save space on the remote node. Thanks for your time.

Answer 1

The most efficient command for you is the TRUNCATE command.

With TRUNCATE, you can chain up tables, like your example:

TRUNCATE tablex, tabley, tablez;

Here’s the description from the postgres docs:

TRUNCATE quickly removes all rows from a set of tables. It has the same effect as an unqualified DELETE on each table, but since it does not actually scan the tables it is faster. Furthermore, it reclaims disk space immediately, rather than requiring a subsequent VACUUM operation. This is most useful on large tables.

You may also add CASCADE as a parameter:

CASCADE Automatically truncate all tables that have foreign-key references to any of the named tables, or to any tables added to the group due to CASCADE.