Re: Efficient slicing/substring of TOAST values (for comment)

John, do you have an updated version of this patch that is ready to be
applied to 7.3?

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John Gray wrote:
> Hi all,
> 
> I attach a patch which adds access routines for efficient extraction of
> parts of TOAST values. 
> 
> The principal additions are two routines in tuptoaster.c,
> heap_tuple_untoast_attr_slice and toast_fetch_datum_slice. The latter
> uses extra index scankeys to retrieve only the TOAST chunks which
> contain the requested substring. This will provide a performance benefit
> if you repeatedly extract small portions (e.g. file headers) from
> TOASTed values, as only one or two chunks will need to be fetched. This
> function is only invoked for external, uncompressed storage.
> 

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