From: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> |
---|---|
To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: eXtensible Transaction Manager API |
Date: | 2015-11-02 12:24:36 |
Message-ID: | 56375604.8030307@postgrespro.ru |
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Thread: | |
Lists: | pgsql-hackers |
On 02.11.2015 12:01, Simon Riggs wrote:
>
> At first I was concerned about recovery, but that looks to be covered.
>
Yes, we have not considered all possible scenarios of working with
PostgreSQL.
We have tested work with different isolation levels: repeatable read and
read committed,
but we have not tested "select for update" and explicit locking.
> PostgreSQL assumes that top-level xid commit is atomic, along with all
> of its subtransactions. So the API having access to only Get/Set at
> the xid level would not work. We would
> need TransactionIdSetTreeStatus() rather than just SetStatus.
> GetStatus is not atomic.
XTM API has function SetTransactionStatus but it actually encapsulate
TransactionIdSetTreeStatus.
> adding 3 addition events to transaction commit callbacks:
>
>
> Those look uncontentious, so we should add those anyway in a sub-patch.
>
> We have also pgDTM implementation which is using timestamps
> (system time) as CSNs.
> It is also based on the same XTM transaction API.
> We will publish it later once we clarify problems with recovery
> and performance with this approach.
>
>
> That is most interesting part, so it needs to be published.
Will be available during this week.
>
> At present, I can't tell whether you need subtrans and multixact calls
> in the API as well. I would imagine we probably do, though we might
> imagine an implementation that didn't support those concepts.
Postgres-XL doesn't support subtransactions. Neither did we at this moment.
Support of subtransactions will be our next step.
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