Thread: Re: pgsql: Check for conflicting queries during replay ofgistvacuumpage()
Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this change. Otherwise, what is going to happen to an unpatched standby (of released versions) that receives the new WAL record from a patched primary? -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
> change. Otherwise, what is going to happen to an unpatched standby (of
> released versions) that receives the new WAL record from a patched
> primary?
We can't change XLOG_PAGE_MAGIC in released branches, surely.
I think the correct thing is just for the release notes to warn people
to upgrade standby servers first.
regards, tom lane
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
> change. Otherwise, what is going to happen to an unpatched standby (of
> released versions) that receives the new WAL record from a patched
> primary?
We can't change XLOG_PAGE_MAGIC in released branches, surely.
I think the correct thing is just for the release notes to warn people
to upgrade standby servers first.
regards, tom lane
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
>> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
>> change. Otherwise, what is going to happen to an unpatched standby (of
>> released versions) that receives the new WAL record from a patched
>> primary?
Oh, and if the answer to your question is not "it fails with an
intelligible error about an unrecognized WAL record type", then we
need to adjust what is emitted so that that will be what happens.
Crashing, or worse silently misprocessing the record, will not do.
regards, tom lane
Alvaro Herrera <alvherre@2ndquadrant.com> writes:
>> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
>> change. Otherwise, what is going to happen to an unpatched standby (of
>> released versions) that receives the new WAL record from a patched
>> primary?
Oh, and if the answer to your question is not "it fails with an
intelligible error about an unrecognized WAL record type", then we
need to adjust what is emitted so that that will be what happens.
Crashing, or worse silently misprocessing the record, will not do.
regards, tom lane
On 2018-Dec-21, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
> > change. Otherwise, what is going to happen to an unpatched standby (of
> > released versions) that receives the new WAL record from a patched
> > primary?
>
> We can't change XLOG_PAGE_MAGIC in released branches, surely.
>
> I think the correct thing is just for the release notes to warn people
> to upgrade standby servers first.
You're right. My memory is playing tricks on me. I recalled that we
had done it to prevent replay of WAL replay in nonpatched standbys in
some backpatched commit, but I can't find any evidence of this :-(
The commit message for 8e9a16ab8f7f (in 9.3 branch after it was
released) says:
In replication scenarios using the 9.3 branch, standby servers must be
upgraded before their master, so that they are prepared to deal with the
new WAL record once the master is upgraded; failure to do so will cause
WAL replay to die with a PANIC message. Later upgrade of the standby
will allow the process to continue where it left off, so there's no
disruption of the data in the standby in any case. Standbys know how to
deal with the old WAL record, so it's okay to keep the master running
the old code for a while.
Stupidly, I checked the 9.4 version of that commit (then the master
branch) and it does indeed contain the XLOG_PAGE_MAGIC change, but the
9.3 commit doesn't.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
On 2018-Dec-21, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this
> > change. Otherwise, what is going to happen to an unpatched standby (of
> > released versions) that receives the new WAL record from a patched
> > primary?
>
> We can't change XLOG_PAGE_MAGIC in released branches, surely.
>
> I think the correct thing is just for the release notes to warn people
> to upgrade standby servers first.
You're right. My memory is playing tricks on me. I recalled that we
had done it to prevent replay of WAL replay in nonpatched standbys in
some backpatched commit, but I can't find any evidence of this :-(
The commit message for 8e9a16ab8f7f (in 9.3 branch after it was
released) says:
In replication scenarios using the 9.3 branch, standby servers must be
upgraded before their master, so that they are prepared to deal with the
new WAL record once the master is upgraded; failure to do so will cause
WAL replay to die with a PANIC message. Later upgrade of the standby
will allow the process to continue where it left off, so there's no
disruption of the data in the standby in any case. Standbys know how to
deal with the old WAL record, so it's okay to keep the master running
the old code for a while.
Stupidly, I checked the 9.4 version of that commit (then the master
branch) and it does indeed contain the XLOG_PAGE_MAGIC change, but the
9.3 commit doesn't.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: pgsql: Check for conflicting queries during replay of gistvacuumpage()
From
Alexander Korotkov
Date:
On Fri, Dec 21, 2018 at 7:09 PM Tom Lane <tgl@sss.pgh.pa.us> wrote: > Alvaro Herrera <alvherre@2ndquadrant.com> writes: > >> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this > >> change. Otherwise, what is going to happen to an unpatched standby (of > >> released versions) that receives the new WAL record from a patched > >> primary? > > Oh, and if the answer to your question is not "it fails with an > intelligible error about an unrecognized WAL record type", then we > need to adjust what is emitted so that that will be what happens. > Crashing, or worse silently misprocessing the record, will not do. Please, note that backpatched version takes special efforts to not introduce new WAL record type. Unpatched standby applies WAL stream of patched primary without any errors, but ignoring conflicts (as it was before) [1]. Patched standby applies the same WAL stream with conflict handling. And I've briefly mentioned that in commit message. "On stable releases we've to be tricky to keep WAL compatibility. Information required for conflict processing is just appended to data of XLOG_GIST_PAGE_UPDATE record. So, PostgreSQL version, which doesn't know about conflict processing, will just ignore that." The thing we can mention in the release notes is that both primary and standby should be upgraded to get conflict handling. If one of them is not upgraded, conflicts will be still missed. Links: 1. https://www.postgresql.org/message-id/CAPpHfdsKS0K8q1sJ-XyMrU%3DL%2Be6XSAOgS09NXp1bQDQts%2Bqz%2Bg%40mail.gmail.com ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company
Re: pgsql: Check for conflicting queries during replay of gistvacuumpage()
From
Alexander Korotkov
Date:
On Fri, Dec 21, 2018 at 7:09 PM Tom Lane <tgl@sss.pgh.pa.us> wrote: > Alvaro Herrera <alvherre@2ndquadrant.com> writes: > >> Hmmm, I'm fairly sure you should have bumped XLOG_PAGE_MAGIC for this > >> change. Otherwise, what is going to happen to an unpatched standby (of > >> released versions) that receives the new WAL record from a patched > >> primary? > > Oh, and if the answer to your question is not "it fails with an > intelligible error about an unrecognized WAL record type", then we > need to adjust what is emitted so that that will be what happens. > Crashing, or worse silently misprocessing the record, will not do. Please, note that backpatched version takes special efforts to not introduce new WAL record type. Unpatched standby applies WAL stream of patched primary without any errors, but ignoring conflicts (as it was before) [1]. Patched standby applies the same WAL stream with conflict handling. And I've briefly mentioned that in commit message. "On stable releases we've to be tricky to keep WAL compatibility. Information required for conflict processing is just appended to data of XLOG_GIST_PAGE_UPDATE record. So, PostgreSQL version, which doesn't know about conflict processing, will just ignore that." The thing we can mention in the release notes is that both primary and standby should be upgraded to get conflict handling. If one of them is not upgraded, conflicts will be still missed. Links: 1. https://www.postgresql.org/message-id/CAPpHfdsKS0K8q1sJ-XyMrU%3DL%2Be6XSAOgS09NXp1bQDQts%2Bqz%2Bg%40mail.gmail.com ------ Alexander Korotkov Postgres Professional: http://www.postgrespro.com The Russian Postgres Company