[Pgcluster-general] pglb stops working when at leat on postmaster dies, why ?

Thu Oct 25 07:57:54 UTC 2007

Hi At,

Am Do 25.10.2007 02:46 schrieb a.mitani at sra-europe.com:

>Hi Holger,
>
>Thank you for interesting test and reporting.
>
>Currentry, I don't have x86_64 environment.
>Therefore, I tested on X86_32 environment as follow as yours.
>However, it has not been occured.
>
>Would you let us know the each configuration files of every servers and
>debug messages of replication server and pglb.

since I am
currently working out of office, I have no access to these files. I will attempt to send them later this week or during the weekend :-)

>
>Regards,
>------------------
>At.Mitani
>
>>I have evaluated the current pgcluster release (1.7.0rc7) under Linux
>>(x86_64).
>>The setup looks like this:
>>machine 1: pgreplicate & pglb
>>machine 2: postmaster (configured as the first machine in pglb and
>>pgreplicate)
>>machine 3: postmaster
>>
>>When I start a pgcbench -i repeatedly in a loop (20 times) everything
>>works fine. I can see connections to machine 2 and 3, so the pglb
>>process really does loadbalance the requests.
>>
>>Now, if I shutdown the postmaster on machine 2 (via pg_ctl stop),
>>during
>>(!) a pgcbench run, something wierd (bad) happens:
>>1. the current pgcbench

>>>>run?is?interrupted?(as?expected),?no?transfer?happens?to?machine?3?(what?might?work
>>eventually)
>>2. the next pgcbench run runs against machine 3 (ok, fine)
>>3.

>>>>all?next?pgcbench?runs?fail?with?the?pglb?telling?me?that?the?cluster?is?down?(what?is?not?true,?since?only?one?postmaster?"died")
>>4. pglb never recovers from this state, the only whay to recover this
>>is
>>to stop pglb, comment out the "dead" postmaster machine and restart
>>pglb
>>
>>Since pglb is supposed to be derived work from pgpool (version 1), I
>>simply added an installation of pgpool to machine 1 and configured it
>>to
>>loadbalance accordingly. Here are the, astonishing, results, when the
>>postmaster on machine 2 is shutown during a pgcbench run:
>>1. the current pgcbench

>>>>run?is?interrupted?(as?expected),?no?transfer?happens?to?machine?3?(what?might?work
>>eventually)
>>2. the next pgcbench run runs against machine 3 (ok, fine)
>>3. all?next?pgcbench?runs?run against machine 3 (fantastic)
>>4. pgpool does completely what I expected from a loadbalancer
>>
>>Furthermore is pgcluster described as follows (see
>>http://pgcluster.projects.postgresql.org/feature.html) for details:
>>"""
>>PGCluster has two functions.
>>- A load sharing function
>>?- The session load of a reference request is distributed. It is
>>effective at the Web application with which a reference request pours
>>in.
>>?- A replication object can be specified per table. When the tables
>>which receive an updating request and a reference request differ, the
>>PGCluster can distribute the table which receives an updating request
>>and can reproduce only the table which receives a reference request.
>>- A high availability function
>>?- When failure occurs in Cluster DB, a load balancer and a
>>replication
>>server separate Failure DB from a system, and continue service using
>>the
>>remaining DB. Since separation of Failure DB and continuation of
>>service
>>are performed simultaneously, most service stop time is made to 0.
>>?- The Cluster DB which repair finished can be dynamically restored to
>>a
>>system, without stopping service.
>>?- Data is automatically copied to DB restored or added from other DB.
>>The query which received during restoration isexecuted from the
>>replication server after restoration.
>>"""
>>Is the latter,?"- When failure occurs in Cluster DB, a load balancer
>>and
>>a replication server separate Failure DB from a system, and continue
>>service using the remaining DB. Since separation of Failure DB and
>>continuation of service are performed simultaneously, most service
>>stop
>>time is made to 0." not true anymore or is it simple a "bug" in the
>>current implementation ?
>>
>>Has anyone attempted this feat and succeeded ? Versions anyone ?
>>
>>I am not afraid to recompile the sourcecode with patches or bugfixes
>>:-)
>>Thanks a lot in advance :-)
>>
>>Regards,
>>Holger
>>
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