Hi Chris,

On 18.08.2017 16:15, Chris Travers wrote:
I would really like to see global indexes.  It would make things a lot
easier for things like unique constraints across table inheritance trees.

On Fri, Aug 18, 2017 at 11:12 AM, Ildar Musin <i.mu...@postgrespro.ru
<mailto:i.mu...@postgrespro.ru>> wrote:

    Hi hackers,

    While we've been developing pg_pathman extension one of the most
    frequent questions we got from our users was about global index
    support. We cannot provide it within an extension. And I couldn't
    find any recent discussion about someone implementing it. So I'm
    thinking about giving it a shot and start working on a patch for

    One possible solution is to create an extended version of item
    pointer which would store relation oid along with block number and

    struct ItemPointerExt
    Oid ip_relid;
    BlockIdData ip_blkid;
    OffsetNumber ip_posid;

    and use it in global index (regular index will still use old
    version). This will require in-depth refactoring of existing index
    nodes to make them support both versions. Accordingly, we could
    replace ItemPointer with ItemPointerExt in index AM to make unified
    API to access both regular and global indexes. TIDBitmap will
    require refactoring as well to be able to deal with relation oids.

So, to be clear on-disk representations would be unchanged for old
indexes (ensuring that pg_upgrade would not be broken), right?

Yes, the idea is to keep old indexes untouched so that there would be no need in any further conversion. And global indexes in turn will have extended TID format.

    It seems to be quite an invasive patch since it requires changes in
    general index routines, existing index nodes, catalog, vacuum
    routines and syntax. So I'm planning to implement it step by step.
    As a first prototype it could be:

    * refactoring of btree index to be able to store both regular and
    extended item pointers;

Do you foresee any performance implementation of handling both?

It's hard to say until there is some working prototype. I think there can be (and most like will be) some overhead due to unified API (and hence addition conversion operations). It will require benchmarking to say how bad is it.

Best Regards,
Chris Travers
Database Administrator

Tel: +49 162 9037 210 | Skype: einhverfr | www.adjust.com
Saarbrücker Straße 37a, 10405 Berlin

Ildar Musin

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