|From:||Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>|
|To:||Pg Hackers <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: pg_serial early wraparound|
|Views:||Raw Message | Whole Thread | Download mbox|
On Mon, Feb 27, 2017 at 7:28 PM, Thomas Munro
> On Wed, Nov 9, 2016 at 11:07 AM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>> The SLRU managed by predicate.c can wrap around and overwrite data if
>> you have more than 1 billion active XIDs. That's because when SSI was
>> implemented, slru.c was limited to four digit segment names, which
>> implied a page limit that wasn't enough for pg_serial to have space
>> for every possible XID. We should probably rip that code out, because
>> SLRUs now support five digit segment names. Something like the
>> attached. I'll post a test script to demonstrate correct wraparound
>> behaviour around in time for one of the later CFs.
> Here is a shell script that shows a full rotation through xid space if
> you build PostgreSQL with TEST_OLDSERXID, which you can do by
> uncommenting a line in predicate.c. On master we see the SLRU
> segments go around the clock twice for each time xid goes around.
> With the patch it goes around just once, adding an extra character to
> the segment name to double the space.
I attached the wrong version. Here is the right one.
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