Re: pageinspect patch, for showing tuple data

Nikolay Shaplov wrote:

> This patch adds several new functions, available from SQL queries. All these
> functions are based on heap_page_items, but accept slightly different
> arguments and has one additional column at the result set:
>
> heap_page_tuples - accepts relation name, and bulkno, and returns usual
> heap_page_items set with additional column that contain snapshot of tuple data
> area stored in bytea.

I think the API around get_raw_page is more useful generally. You might
have table blocks stored in a bytea column for instance, because you
extracted from some remote server and inserted into a local table for
examination. If you only accept relname/blkno, there's no way to
examine data other than blocks directly in the database dir, which is
limiting.

> There is also one strange function: _heap_page_items it is useless for
> practical purposes. As heap_page_items it accepts page data as bytea, but also
> get a relation name. It tries to apply tuple descriptor of that relation to
> that page data.

For BRIN, I added something similar (brin_page_items), but it receives
the index OID rather than name, and constructs a tuple descriptor to
read the data. I think OID is better than name generally. (You can
cast the relation name to regclass).

It's easy to misuse, but these functions are superuser-only, so there
should be no security issue at least. The possibility of a crash
remains real, though, so maybe we should try to come up with a way to
harden that.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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