[pgpool-general: 3853] Re: Pgpool Cache Invaliadtion Problems
Tatsuo Ishii
ishii at postgresql.org
Tue Jul 7 10:46:31 JST 2015
As I wrote before, it's limitation of current query cache
implementation. That might be solved in the future release.
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
> Hi all,
>
> I saw the email thread below and suspect I am experiencing the same or
> a similar problem. I am running 2 independent pgpool instances on
> separate servers against a primary/hot standby postgres pair. The two
> pgpools don't seem to recognize each other's cache invalidating
> activity. (I have enable_query_cache = true, load_balance_mode = on,
> master_slave_mode = on and pgpool regclass installed on both PG
> servers.) Do I really have to turn caching off, or can watchdog or
> something else resolve this problem?
>
> The example below shows updates on pgpool 1 not being recognized by
> the pgpool 2:
>
> / From PGP1 create table family(name text);
> // From PGP1 insert into family values('Bob');////
> From PGP1 select * from family;
> --> Bob/
> /// From PGP2 select * from family;
> --> Bob
> /
> F//////rom PGP1 insert into family values('Sally');//
> From PGP1 insert into family values('Mike');//
> // From PGP1 select * from family;
> --> Bob
> --> Sally
> --> Mike
> / From PGP2 select * from family;
> --> Bob/
>
> As the existing system was given to me, I am required to receive
> transactions from two Tomcat servers into 2 independent Pgpools.
>
> ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐
>
> ││
>
> │ACE│
>
> ││
>
> └ ─ ─ ─ ─ ─ ─ ─ ─ ┘
>
> / \
>
> /\
>
> /\
>
> ˅˅
>
> ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐
>
> ││││
>
> │ TOMCAT SERVER ││TOMCAT SERVER │
>
> ││││
>
> │ PGPOOL INST 1 ││PGPOOL INST 2│
>
> │(ACTIVE/INDEPEN.)││(ACTIVE/INDEPEN.)│
>
> └ ─ ─ ─ ─ ─ ─ ─ ─ ┘└ ─ ─ ─ ─ ─ ─ ─ ─ ┘
>
> │\ /│
>
> READ │ WRITE \/READ │ ONLY
>
> │ /\│
>
> │/ \│
>
> ˅˅˅˅
>
> ┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐┌ ─ ─ ─ ─ ─ ─ ─ ─ ┐
>
> ││││
>
> │ POSTGRES SERVER ││ POSTGRES SERVER │
>
> ││││
>
> │ PGPOOL PRIM ││ PG HOT STANDBY│
>
> ││││
>
> └ ─ ─ ─ ─ ─ ─ ─ ─ ┘└ ─ ─ ─ ─ ─ ─ ─ ─ ┘
>
>
> Thanks,
>
> Mike Hill
> LMCO, Herndon, VA
>
>
> [pgpool-general: 3676] Re: Error in pgpool memory cache invalidation.
>
> *Tatsuo Ishii* ishii at postgresql.org
> *<mailto:pgpool-general%40pgpool.net?Subject=Re:%20Re%3A%20%5Bpgpool-general%3A%203676%5D%20Re%3A%20Error%20in%20pgpool%20memory%20cache%0A%20invalidation.&In-Reply-To=%3C20150430.182247.762685084071967340.t-ishii%40sraoss.co.jp%3E>
> /Thu Apr 30 18:22:47 JST 2015/
>
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>
>
> ------------------------------------------------------------------------
>
> Hum. You are right. Consider following scenario:
>
> 1) pgpool-II A receives "SELECT * FROM t1 ..." and create a cache on
> memecached
>
> 2) pgpool-II B receives "UPDATE t1 ..." and tries to invalidate the
> query cache created at #1.
>
> #2 will fail because pgpool-II B does not have the table oid file.
>
> We need to have a way to share info among A & B regarding table
> oids. In the mean time is it possible for you to send write queries
> only one of A or B? This will avoid the problem above.
>
> Best regards,
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English:http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
>
>>/ Hi,
> />/ />>/ From my intial reading of the source code,
> />/ />/ 1. For every query cached memcached writes the cache-key on
> />/ oidir/<db_oid>/<table_oid>
> />/ 2. If there is an update on a table, read each hash from
> <Table_oid> file
> />/ and delete in memcache.
> />/ />/ If this is what pgpool uses to invalidate cache - two pgpools,
> using same
> />/ memcache will not invalidate cache properly. Please correct me if
> there are
> />/ more to this logic.
> />/ />/ />/ />/ />/ />/ />/ />/ />/ *DHANANJAY *| Infrastructure
> Engineer
> />/ Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />/ Web: www.plivo.com | Twitter: @plivo <http://twitter.com/plivo>,
> />/ @notmycommit <https://twitter.com/notmycommit>
> />/ />/ Free Incoming SMS for All US Short Codes – Get One Today!
> />/ <https://www.plivo.com/sms-short-code/?utm=emailsig>
> />/ />/ />/ />/ On Wed, Apr 29, 2015 at 4:10 AM, Tatsuo Ishii <ishii
> at postgresql.org
> <http://www.sraoss.jp/mailman/listinfo/pgpool-general>> wrote:
> />/ />>/ Probably pgpool log with -d (debugging option) turned on will
> provide
> />>/ more useful information.
> />>/
> />>/ Best regards,
> />>/ --
> />>/ Tatsuo Ishii
> />>/ SRA OSS, Inc. Japan
> />>/ English:http://www.sraoss.co.jp/index_en.php
> />>/ Japanese:http://www.sraoss.co.jp
> />>/
> />>/ > Message got clipped again. Resending
> />>/ >
> />>/ > Hi,
> />>/ >
> />>/ > This commit seems to have fixed the issue. However cache
> invalidation
> />>/ when
> />>/ > multiple pgpools are used (connecting to same memcache server)
> is (?)
> />>/ > broken even with 3.3.5. Here are the logs from 3.3.5
> />>/ >
> />>/ >https://gist.github.com/dbalan/c5a93458d5c091c28c71
> />>/ >
> />>/ > My test setup is two instances of 3.3.5 running on 9999 and
> 9988 of same
> />>/ > machine with memcache running in localhost.
> />>/ >
> />>/ > Logs:
> />>/ >
> />>/ >>From first pgpool,
> />>/ > # First, read and update data - invalidates cache - this works
> fine.
> />>/ > psql -U ruser -d mydb -h 127.0.0.1 -p 9999
> />>/ > Password for user ruser:
> />>/ > psql (9.4.1)
> />>/ > Type "help" for help.
> />>/ >
> />>/ > mydb=> select comments from users where id=1;
> />>/ > comments
> />>/ > ----------------
> />>/ > boot me please
> />>/ > (1 row)
> />>/ >
> />>/ > mydb=> update users set comments='hello' where id=1;
> />>/ > UPDATE 1
> />>/ > mydb=> select comments from users where id=1;
> />>/ > comments
> />>/ > ----------
> />>/ > hello
> />>/ > (1 row)
> />>/ >
> />>/ > mydb=>
> />>/ >
> />>/ >
> />>/ > Second pgpool:
> />>/ > # Connects via second deamon, reads stale data, i/e updates
> from this
> />>/ > pgpool instance never invalidate cache.
> />>/ > λ ~/ psql -U ruser -d mydb -h 127.0.0.1 -p 9988
> />>/ > Password for user ruser:
> />>/ > psql (9.4.1)
> />>/ > Type "help" for help.
> />>/ >
> />>/ > mydb=> select comments from users where id=1;
> />>/ > comments
> />>/ > ----------
> />>/ > hello
> />>/ > (1 row)
> />>/ >
> />>/ > mydb=> update users set comments='hello world' where id=1;
> />>/ > UPDATE 1
> />>/ > mydb=> select comments from users where id=1;
> />>/ > comments
> />>/ > ----------
> />>/ > hello
> />>/ > (1 row)
> />>/ >
> />>/ > mydb=>
> />>/ >
> />>/ >
> />>/ > The configs and full logs are attached in the link, They both
> are same
> />>/ > except for the directory paths and ports - not sure whats going
> wrong
> />>/ here.
> />>/ >
> />>/ >
> />>/ > *DHANANJAY *| Infrastructure Engineer
> />>/ > Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />>/ > Web: www.plivo.com | Twitter: @plivo
> <http://twitter.com/plivo>,
> />>/ > @notmycommit <https://twitter.com/notmycommit>
> />>/ >
> />>/ > Free Incoming SMS for All US Short Codes – Get One Today!
> />>/ > <https://www.plivo.com/sms-short-code/?utm=emailsig>
> />>/ >
> />>/ > On Mon, Apr 27, 2015 at 5:29 PM, Dhananjay Balan <dhananjay at
> plivo.com <http://www.sraoss.jp/mailman/listinfo/pgpool-general>>
> />>/ > wrote:
> />>/ >
> />>/ >> Hi,
> />>/ >>
> />>/ >> This commit seems to have fixed the issue. However cache
> invalidation
> />>/ when
> />>/ >> multiple pgpools are used (connecting to same memcache server)
> is (?)
> />>/ >> broken even with 3.3.5. Here are the logs from 3.3.5
> />>/ >>
> />>/ >>https://gist.github.com/dbalan/c5a93458d5c091c28c71
> />>/ >>
> />>/ >> My test setup is two instances of 3.3.5 running on 9999 and
> 9988 of same
> />>/ >> machine with memcache running in localhost.
> />>/ >>
> />>/ >> From first pgpool,
> />>/ >>
> />>/ >> # First, read and update data - invalidates cache - this works
> fine.
> />>/ >> psql -U ruser -d mydb -h 127.0.0.1 -p 9999
> />>/ >> Password for user ruser:
> />>/ >> psql (9.4.1)
> />>/ >> Type "help" for help.
> />>/ >>
> />>/ >> mydb=> select comments from users where id=1;
> />>/ >> comments
> />>/ >> ----------------
> />>/ >> boot me please
> />>/ >> (1 row)
> />>/ >>
> />>/ >> mydb=> update users set comments='hello' where id=1;
> />>/ >> UPDATE 1
> />>/ >> mydb=> select comments from users where id=1;
> />>/ >> comments
> />>/ >> ----------
> />>/ >> hello
> />>/ >> (1 row)
> />>/ >>
> />>/ >> mydb=>
> />>/ >>
> />>/ >>
> />>/ >> Second pgpool:
> />>/ >> # Connects via second deamon, reads stale data, i/e updates
> from this
> />>/ >> pgpool instance never invalidate cache.
> />>/ >> λ ~/ psql -U ruser -d mydb -h 127.0.0.1 -p 9988
> />>/ >> Password for user ruser:
> />>/ >> psql (9.4.1)
> />>/ >> Type "help" for help.
> />>/ >>
> />>/ >> mydb=> select comments from users where id=1;
> />>/ >> comments
> />>/ >> ----------
> />>/ >> hello
> />>/ >> (1 row)
> />>/ >>
> />>/ >> mydb=> update users set comments='hello world' where id=1;
> />>/ >> UPDATE 1
> />>/ >> mydb=> select comments from users where id=1;
> />>/ >> comments
> />>/ >> ----------
> />>/ >> hello
> />>/ >> (1 row)
> />>/ >>
> />>/ >> mydb=>
> />>/ >>
> />>/ >>
> />>/ >> The configs and full logs are attached in the link, They both
> are same
> />>/ >> except for the directory paths and ports - not sure whats
> going wrong
> />>/ here.
> />>/ >>
> />>/ >>https://gist.github.com/dbalan/c5a93458d5c091c28c71
> />>/ >>
> />>/ >>
> />>/ >>
> />>/ >>
> />>/ >> *DHANANJAY *| Infrastructure Engineer
> />>/ >> Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />>/ >> Web: www.plivo.com | Twitter: @plivo
> <http://twitter.com/plivo>,
> />>/ >> @notmycommit <https://twitter.com/notmycommit>
> />>/ >>
> />>/ >> Free Incoming SMS for All US Short Codes – Get One Today!
> />>/ >> <https://www.plivo.com/sms-short-code/?utm=emailsig>
> />>/ >>
> />>/ >>
> />>/ >>
> />>/ >> On Thu, Apr 23, 2015 at 5:11 PM, Muhammad Usama <m.usama at
> gmail.com <http://www.sraoss.jp/mailman/listinfo/pgpool-general>>
> />>/ wrote:
> />>/ >>
> />>/ >>> Hi
> />>/ >>>
> />>/ >>> I have found the problem, It was because of the buffer for
> storing
> />>/ table
> />>/ >>> oids was created in wrong memory context.
> />>/ >>> I have pushed the fix for it in master and 3_4 stable
> branches.
> />>/ >>>
> />>/ >>> Thanks
> />>/ >>> Best regards
> />>/ >>> Muhammad Usama
> />>/ >>>
> />>/ >>>
> />>/ >>> On Wed, Apr 22, 2015 at 2:09 PM, Tatsuo Ishii <ishii at
> postgresql.org <http://www.sraoss.jp/mailman/listinfo/pgpool-general>>
> />>/ >>> wrote:
> />>/ >>>
> />>/ >>>> Thanks for the report.
> />>/ >>>>
> />>/ >>>> I confirm this with pgpool-II 3.4.1. I also found that this
> does not
> />>/ >>>> happen with 3.3.5 (I tested with shmem).
> />>/ >>>>
> />>/ >>>> Here is the test script.
> />>/ >>>> -------------------------------------
> />>/ >>>> drop table t1;
> />>/ >>>> create table t1(i int, j text);
> />>/ >>>> insert into t1 values(1, 'aaa');
> />>/ >>>> select * from t1;
> />>/ >>>> select * from t1;
> />>/ >>>> update t1 set j = 'bbb' where i = 1;
> />>/ >>>> select * from t1;
> />>/ >>>> -------------------------------------
> />>/ >>>>
> />>/ >>>> Will look into this...
> />>/ >>>>
> />>/ >>>> Best regards,
> />>/ >>>> --
> />>/ >>>> Tatsuo Ishii
> />>/ >>>> SRA OSS, Inc. Japan
> />>/ >>>> English:http://www.sraoss.co.jp/index_en.php
> />>/ >>>> Japanese:http://www.sraoss.co.jp
> />>/ >>>>
> />>/ >>>> > Looks like only part of this email ended up in the mailing
> list ,
> />>/ not
> />>/ >>>> > sure how. Resending again - hope it works this time.
> />>/ >>>> >
> />>/ >>>> > pgpool doesn't seem to be invalidating caches
> properly. See the
> />>/ >>>> > example test case below
> />>/ >>>> >
> />>/ >>>> > psql -U ruser -d mydb -h 127.0.0.1 -p 9999
> />>/ >>>> > Password for user ruser:
> />>/ >>>> > psql (9.4.1)
> />>/ >>>> > Type "help" for help.
> />>/ >>>> >
> />>/ >>>> > mydb=> select comments from users where id=1;
> />>/ >>>> > comments
> />>/ >>>> > ----------
> />>/ >>>> > boooo
> />>/ >>>> > (1 row)
> />>/ >>>> >
> />>/ >>>> > # comes from cache
> />>/ >>>> > mydb=> select comments from users where id=1;
> />>/ >>>> > comments
> />>/ >>>> > ----------
> />>/ >>>> > boooo
> />>/ >>>> > (1 row)
> />>/ >>>> >
> />>/ >>>> > # works
> />>/ >>>> > mydb=> update users set comments='hello' where id=1;
> />>/ >>>> > UPDATE 1
> />>/ >>>> > mydb=> select comments from users where id=1;
> />>/ >>>> > comments
> />>/ >>>> > ----------
> />>/ >>>> > hello
> />>/ >>>> > (1 row)
> />>/ >>>> >
> />>/ >>>> > # stale
> />>/ >>>> > mydb=> update users set comments='hello world' where id=1;
> />>/ >>>> > UPDATE 1
> />>/ >>>> > mydb=> select comments from users where id=1;
> />>/ >>>> > comments
> />>/ >>>> > ----------
> />>/ >>>> > hello
> />>/ >>>> > (1 row)
> />>/ >>>> >
> />>/ >>>> > # also stale
> />>/ >>>> > mydb=> update users set comments='booo' where id=1;
> />>/ >>>> > UPDATE 1
> />>/ >>>> > mydb=> select comments from users where id=1;
> />>/ >>>> > comments
> />>/ >>>> > ----------
> />>/ >>>> > hello
> />>/ >>>> > (1 row)
> />>/ >>>> >
> />>/ >>>> >
> />>/ >>>> > From the second write onwards, the cache is not
> invalidated and
> />>/ stale
> />>/ >>>> > value is being served. Is it a bug or am I doing something
> wrong?
> />>/ This
> />>/ >>>> > happens with both cache backends (memcache and shmem but
> test logs
> />>/ are
> />>/ >>>> > from memcache backend)
> />>/ >>>> >
> />>/ >>>> > Test setup is postgresql-9.4 and memcached 1.4.21 and
> pgpool-3.4.2.
> />>/ my
> />>/ >>>> > configs and logs from test are here
> />>/ >>>> >
> />>/ >>>> >https://gist.github.com/dbalan/d635993a3e532a083751
> />>/ >>>> >
> />>/ >>>> > Regards,
> />>/ >>>> > --------
> />>/ >>>> > DHANANJAY | Infrastructure Engineer
> />>/ >>>> > Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />>/ >>>> > Web: www.plivo.com | Twitter: @plivo, @notmycommit
> />>/ >>>> > DHANANJAY | Infrastructure Engineer
> />>/ >>>> > Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />>/ >>>> > Web: www.plivo.com | Twitter: @plivo, @notmycommit
> />>/ >>>> >
> />>/ >>>> > Free Incoming SMS for All US Short Codes – Get One Today!
> />>/ >>>> >
> />>/ >>>> >
> />>/ >>>> >
> />>/ >>>> >
> />>/ >>>> > On Tue, Apr 21, 2015 at 12:33 PM, Dhananjay Balan <
> />>/ dhananjay at plivo.com
> <http://www.sraoss.jp/mailman/listinfo/pgpool-general>>
> />>/ >>>> wrote:
> />>/ >>>> >> pgpool doesn't seem to be invalidating caches
> properly. See the
> />>/ >>>> >> example test case below
> />>/ >>>> >>
> />>/ >>>> >> psql -U ruser -d mydb -h 127.0.0.1 -p 9999
> />>/ >>>> >> Password for user ruser:
> />>/ >>>> >> psql (9.4.1)
> />>/ >>>> >> Type "help" for help.
> />>/ >>>> >>
> />>/ >>>> >> mydb=> select comments from users where id=1;
> />>/ >>>> >> comments
> />>/ >>>> >> ----------
> />>/ >>>> >> boooo
> />>/ >>>> >> (1 row)
> />>/ >>>> >>
> />>/ >>>> >> # comes from cache
> />>/ >>>> >> mydb=> select comments from users where id=1;
> />>/ >>>> >> comments
> />>/ >>>> >> ----------
> />>/ >>>> >> boooo
> />>/ >>>> >> (1 row)
> />>/ >>>> >>
> />>/ >>>> >> # works
> />>/ >>>> >> mydb=> update users set comments='hello' where id=1;
> />>/ >>>> >> UPDATE 1
> />>/ >>>> >> mydb=> select comments from users where id=1;
> />>/ >>>> >> comments
> />>/ >>>> >> ----------
> />>/ >>>> >> hello
> />>/ >>>> >> (1 row)
> />>/ >>>> >>
> />>/ >>>> >> # stale
> />>/ >>>> >> mydb=> update users set comments='hello world' where
> id=1;
> />>/ >>>> >> UPDATE 1
> />>/ >>>> >> mydb=> select comments from users where id=1;
> />>/ >>>> >> comments
> />>/ >>>> >> ----------
> />>/ >>>> >> hello
> />>/ >>>> >> (1 row)
> />>/ >>>> >>
> />>/ >>>> >> # also stale
> />>/ >>>> >> mydb=> update users set comments='booo' where id=1;
> />>/ >>>> >> UPDATE 1
> />>/ >>>> >> mydb=> select comments from users where id=1;
> />>/ >>>> >> comments
> />>/ >>>> >> ----------
> />>/ >>>> >> hello
> />>/ >>>> >> (1 row)
> />>/ >>>> >>
> />>/ >>>> >>
> />>/ >>>> >> From the second write onwards, the cache is not
> invalidated and
> />>/ stale
> />>/ >>>> >> value is being served. Is it a bug or am I doing
> something wrong?
> />>/ This
> />>/ >>>> >> happens with both cache backends (memcache and shmem but
> test logs
> />>/ are
> />>/ >>>> >> from memcache backend)
> />>/ >>>> >>
> />>/ >>>> >> Test setup is postgresql-9.4 and memcached 1.4.21 and
> />>/ pgpool-3.4.2. my
> />>/ >>>> >> configs and logs from test are here
> />>/ >>>> >>
> />>/ >>>> >>https://gist.github.com/dbalan/d635993a3e532a083751
> />>/ >>>> >>
> />>/ >>>> >> Regards,
> />>/ >>>> >> --------
> />>/ >>>> >> DHANANJAY | Infrastructure Engineer
> />>/ >>>> >> Plivo, Inc. 340 Pine St, San Francisco - 94104, USA
> />>/ >>>> >> Web: www.plivo.com | Twitter: @plivo, @notmycommit
> />>/ >>>> > _______________________________________________
> />>/ >>>> > pgpool-general mailing list
> />>/ >>>> >pgpool-general at pgpool.net
> <http://www.sraoss.jp/mailman/listinfo/pgpool-general>
> />>/ >>>> >http://www.pgpool.net/mailman/listinfo/pgpool-general
> />>/ >>>> _______________________________________________
> />>/ >>>> pgpool-general mailing list
> />>/ >>>>pgpool-general at pgpool.net
> <http://www.sraoss.jp/mailman/listinfo/pgpool-general>
> />>/ >>>>http://www.pgpool.net/mailman/listinfo/pgpool-general
> />>/ >>>>
> />>/ >>>
> />>/ >>>
> />>/ >>
> />>/
> /
>
> ------------------------------------------------------------------------
>
> * Previous message: [pgpool-general: 3670] Re: Error in pgpool memory
> cache invalidation.
> <http://www.sraoss.jp/pipermail/pgpool-general/2015-April/003722.html>
> * Next message: [pgpool-general: 3646] Re: Adding a New Server and
> Recovery
> <http://www.sraoss.jp/pipermail/pgpool-general/2015-April/003695.html>
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>
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