On Thu, Apr 14, 2011 at 7:42 PM, Adrian Klaver <adrian.klaver@xxxxxxxxx> wrote: > On Thursday, April 14, 2011 5:51:21 pm Yang Zhang wrote: > >> > > >> > adrian.klaver@xxxxxxxxx > >> > >> Already know about TOAST. I could've been clearer, but that's not the > >> same as the block-/page-level compression I was referring to. > > I am obviously missing something. The TOAST mechanism is designed to keep > tuple data below the default 8KB page size. In fact it kicks in at a lower > level than that: > > "The TOAST code is triggered only when a row value to be stored in a table > is wider than TOAST_TUPLE_THRESHOLD bytes (normally 2 kB). The TOAST code > will compress and/or move field values out-of-line until the row value is > shorter than TOAST_TUPLE_TARGET bytes (also normally 2 kB) or no more gains > can be had. During an UPDATE operation, values of unchanged fields are > normally preserved as-is; so an UPDATE of a row with out-of-line values > incurs no TOAST costs if none of the out-of-line values change.' > > Granted no all data types are TOASTable. Are you looking for something more > aggressive than that? Yes. http://blog.oskarsson.nu/2009/03/hadoop-feat-lzo-save-disk-space-and.html http://wiki.apache.org/hadoop/UsingLzoCompression http://dev.mysql.com/doc/innodb-plugin/1.0/en/innodb-compression-internals-algorithms.html > > -- > > Adrian Klaver > > adrian.klaver@xxxxxxxxx -- Yang Zhang http://yz.mit.edu/ -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
