Re: TOAST-slicing: substring access methods for TOASTed values.

Patch applied.  I discussed this with Jan and Tom and both liked the
idea.  Thanks.

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John Gray wrote:
> Hi all,
> 
> I attach a version of my toast-slicing patch, against current CVS
> (current as of a few hours ago.)
> 
> This patch:
> 
> 1. Adds PG_GETARG_xxx_P_SLICE() macros and associated support routines.
> 
> 2. Adds routines in src/backend/access/tuptoaster.c for fetching only
> necessary chunks of a toasted value. (Modelled on latest changes to
> assume chunks are returned in order).
> 
> 3. Amends text_substr and bytea_substr to use new methods. It now
> handles multibyte cases -and should still lead to a performance
> improvement in the multibyte case where the substring is near the
> beginning of the string.
> 
> 4. Added new command: ALTER TABLE tabname ALTER COLUMN colname SET
> STORAGE {PLAIN | EXTERNAL | EXTENDED | MAIN} to parser and documented in
> alter-table.sgml. (NB I used ColId as the item type for the storage
> mode string, rather than a new production - I hope this makes sense!).
> All this does is sets attstorage for the specified column.
> 
> 4. AlterTableAlterColumnStatistics is now AlterTableAlterColumnFlags and
> handles both statistics and storage (it uses the subtype code to
> distinguish). The previous version of my patch also re-arranged other
> code in backend/commands/command.c but I have dropped that from this
> patch.(I plan to return to it separately).
> 
> 5. Documented new macros (and also the PG_GETARG_xxx_P_COPY macros) in
> xfunc.sgml. ref/alter_table.sgml also contains documentation for ALTER
> COLUMN SET STORAGE.
> 
> Comments or suggestions welcome.
> 
> John
> 
> 
> 
> 
> 

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