CLEAR_CACHES

Clears the Vertica internal cache files.

Syntax

CLEAR_CACHES ( )

Privileges

Superuser

Notes

If you want to run benchmark tests for your queries, in addition to clearing the internal Vertica cache files, clear the Linux file system cache. The kernel uses unallocated memory as a cache to hold clean disk blocks. If you are running version 2.6.16 or later of Linux and you have root access, you can clear the kernel file system cache as follows:

  1. Make sure that all data in the cache is written to disk: 

    # sync

  2. Writing to the drop_caches file causes the kernel to drop clean caches, entries, and inodes from memory, causing that memory to become free, as follows:

    • To clear the page cache:

      # echo 1 > /proc/sys/vm/drop_caches

    • To clear the entries and inodes:

      # echo 2 > /proc/sys/vm/drop_caches

    • To clear the page cache, entries, and inodes:

      # echo 3 > /proc/sys/vm/drop_caches

Example

The following example clears the Vertica internal cache files:

=> SELECT CLEAR_CACHES();
 CLEAR_CACHES
--------------
 Cleared
(1 row)