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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? -- Adrian Klaver adrian.klaver@xxxxxxxxx |
