Horton

Re: Large expressions in indexes can't be stored (non-TOASTable)

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "Jonathan S. Katz" <jkatz@postgresql.org>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Michael Paquier <michael@paquier.xyz>
Date: 2024-09-23T15:50:21Z
Lists: pgsql-hackers

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On Mon, Sep 23, 2024 at 04:00:00PM +0300, Alexander Lakhin wrote:
> I tested it with two code modifications (1st is to make each created
> expression index TOASTed (by prepending 1M of spaces to the indexeprs
> value) and 2nd to make each created index an expression index (by
> modifying index_elem_options in gram.y) - both modifications are kludgy so
> I don't dare to publish them) and found no other snapshot-related issues
> during `make check-world`.

Thanks.  Here is an updated patch with tests and comments.  I've also moved
the calls to PushActiveSnapshot()/PopActiveSnapshot() to surround only the
section of code where the snapshot is needed.  Besides being more similar
in style to other fixes I found, I think this is safer because much of this
code is cautious to avoid deadlocks.  For example, DefineIndex() has the
following comment:

	/*
	 * The snapshot subsystem could still contain registered snapshots that
	 * are holding back our process's advertised xmin; in particular, if
	 * default_transaction_isolation = serializable, there is a transaction
	 * snapshot that is still active.  The CatalogSnapshot is likewise a
	 * hazard.  To ensure no deadlocks, we must commit and start yet another
	 * transaction, and do our wait before any snapshot has been taken in it.
	 */

I carefully inspected all the code paths this patch touches, and I think
I've got all the details right, but I would be grateful if someone else
could take a look.

-- 
nathan

Commits

  1. Ensure we have a snapshot when updating various system catalogs.

  2. Remove pg_replication_origin's TOAST table.

  3. Restrict password hash length.

  4. Ensure we have a snapshot when updating pg_index entries.

  5. Add TOAST table to pg_index.

  6. Add toast tables to most system catalogs