Re: Applying TOAST to CURRENT

> Hi,
>
> now that we have the branch for 7.0, I could apply my actual
> work on TOAST to the CURRENT development tree. Before doing
> so, I'd like to discuss some related details.
>
> 1. In the actual version, the lztext datatype is stripped
> down to something more similar to text (does not compress
> on input). So it is kinda toastable base type for testing
> purposes created at initdb time.
>
> The pg_rules catalog still uses it, just that the toaster
> is now responsible to do the compression work. No
> problems so far with that.
>
> In the long run I think lztext will disappear completely
> again (it was supposed to be). Does anybody see a problem
> with abuse of this type during development?

Sounds fine.

> 2. I've added another ALTER TABLE command to create the
> external storage table for a relation. The syntax is
>
> ALTER TABLE tablename CREATE TOAST TABLE;
>
> Up to that, toastable types (lztext only yet) will be
> compressed, but the INSERT still fails if compression
> isn't enough to make a tuple fit.
>
> We haven't decided yet how/when to create the secondary
> relation and it's index. Since we intend to make base
> types like text and varchar by default toastable, I don't
> think that "if a tables schema contains toastable types"
> is a good enough reason to create them silently. There
> might exists tons of tables in a schema, that don't
> require it.
>
> OTOH I don't think it's a good thing to try creating
> these things on the fly the first time needed. The
> required catalog changes and file creations introduce all
> kinds of possible rollback/crash problems, that we don't
> want to have here - do we?

Well, we could print the message suggesing ALTER TABLE when printing
tuple too large. Frankly, I don't see a problem in creating the backup
table automatically. If you are worried about performance, how about
putting it in a subdirectory.

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Bruce Momjian | http://www.op.net/~candle
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