Re: 64-bit TXID?

On Thu, Sep 18, 2014 at 9:17 PM, cowwoc <cowwoc@bbs.darktech.org> wrote:
> I did a quick search and noticed that 8 years ago, a Skype employee provided
> a patch for migrating to a 64-bit TXID:
> http://postgresql.1045698.n5.nabble.com/RFC-txid-module-for-64-bit-external-transaction-IDs-tt1947503.html

Actually, this patch was supposed to:

"""
The goal is to make PostgreSQL internal transaction ID and snapshot
data usable externally.  They cannot be used directly as the
internal 4-byte value wraps around and thus breaks indexing.
"""

This stuff was committed to PostgreSQL in essentially the same form years ago:

http://www.postgresql.org/docs/devel/static/functions-info.html#FUNCTIONS-TXID-SNAPSHOT

It's just a way of getting a stable 64-bit xid value for external use,
by adding an epoch count to the representation. Nothing more.

The most obvious reason for not using 64-bit xid values is that they
require more storage than 32-bit values. There is a patch floating
around that makes it safe to not forcibly safety shutdown the server
where currently it is necessary, but it doesn't work by making xids
64-bit.

--
Regards,
Peter Geoghegan