[pgpool-general: 440] Re: strange load balancing issue in Solaris
Aravinth
aravinth at mafiree.com
Thu May 10 11:14:18 JST 2012
It's working.
Regards,
Aravinth
On Wed, May 9, 2012 at 5:26 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
> Thanks for the hint. Attached is a patch trying to fix the
> problem. Can you please try it?
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
>
> > Yes the issue is with random() function.
> >
> > Looks like I have solved the problem by using rand.
> >
> > Regards,
> > Aravinth
> >
> >
> > On Wed, May 9, 2012 at 4:02 PM, Tatsuo Ishii <ishii at postgresql.org>
> wrote:
> >
> >> Thanks. Apparently random() of Solaris could return value beyond
> >> RAND_MAX! It's easy to fix the problem, but I would like to do it with
> >> respcet to portability. Any idea?
> >> --
> >> Tatsuo Ishii
> >> SRA OSS, Inc. Japan
> >> English: http://www.sraoss.co.jp/index_en.php
> >> Japanese: http://www.sraoss.co.jp
> >>
> >> >>From Solaris 10 (x86) man page:
> >> >
> >> >
> >> > SYNOPSIS
> >> > #include <stdlib.h>
> >> >
> >> > long random(void);
> >> >
> >> > void srandom(unsigned int seed);
> >> >
> >> > char *initstate(unsigned int seed, char *state, size_t
> >> > size);
> >> >
> >> > char *setstate(const char *state);
> >> >
> >> > DESCRIPTION
> >> > The random() function uses a nonlinear additive feedback
> >> > random-number generator employing a default state array size
> >> > of 31 long integers to return successive pseudo-random
> >> > numbers in the range from 0 to 2**31 -1. The period of this
> >> > random-number generator is approximately 16 x (2 **31 -1).
> >> > The size of the state array determines the period of the
> >> > random-number generator. Increasing the state array size
> >> > increases the period.
> >> >
> >> > The srandom() function initializes the current state array
> >> > using the value of seed.
> >> >
> >> >
> >> > (...)
> >> >
> >> >
> >> >
> >> > Regards,
> >> > Rafal
> >> >
> >> >
> >> >
> >> > -----Original Message-----
> >> > From: pgpool-general-bounces at pgpool.net [mailto:
> >> pgpool-general-bounces at pgpool.net] On Behalf Of Tatsuo Ishii
> >> > Sent: Wednesday, May 09, 2012 11:44 AM
> >> > To: caravinth at gmail.com
> >> > Cc: pgpool-general at pgpool.net
> >> > Subject: [pgpool-general: 431] Re: strange load balancing issue in
> >> Solaris
> >> >
> >> > Thanks.
> >> >
> >> > 2012-05-09 14:31:48 LOG: pid 22459: r: 268356063.000000
> total_weight:
> >> 32767.000000
> >> >
> >> > This is really weird. Here pgpool caculate this:
> >> >
> >> > r = (((double)random())/RAND_MAX) * total_weight;
> >> >
> >> > Total weight is same as RAND_MAX. It seems your random() returns
> >> > bigger than RAND_MAX, which does not make sense because man page of
> >> > random(3) on my Linux says:
> >> >
> >> > The random() function uses a non-linear additive feedback
> >> random number
> >> > generator employing a default table of size 31 long integers
> to
> >> return
> >> > successive pseudo-random numbers in the range from 0 to
> RAND_MAX.
> >> The
> >> > period of this random number generator is very large,
> >> approximately
> >> > 16 * ((2^31) - 1).
> >> >
> >> > What does your man page for random() say on your system?
> >> > --
> >> > Tatsuo Ishii
> >> > SRA OSS, Inc. Japan
> >> > English: http://www.sraoss.co.jp/index_en.php
> >> > Japanese: http://www.sraoss.co.jp
> >> >
> >> >> Sorry . I missed it.
> >> >>
> >> >> Here is the log file.
> >> >>
> >> >> --Aravinth
> >> >>
> >> >>
> >> >> On Wed, May 9, 2012 at 2:07 PM, Tatsuo Ishii <ishii at postgresql.org>
> >> wrote:
> >> >>
> >> >>> > The code you have sent is same in child.c.
> >> >>>
> >> >>> No.
> >> >>>
> >> >>> pool_log("r: %f total_weight: %f", r, total_weight);
> >> >>>
> >> >>> You need to add the line above to get usefull information.
> >> >>> --
> >> >>> Tatsuo Ishii
> >> >>> SRA OSS, Inc. Japan
> >> >>> English: http://www.sraoss.co.jp/index_en.php
> >> >>> Japanese: http://www.sraoss.co.jp
> >> >>>
> >> >>>
> >> >>> > I have attached the log file. Please check
> >> >>> >
> >> >>> >
> >> >>> > --Aravinth
> >> >>> >
> >> >>> >
> >> >>> > On Tue, May 8, 2012 at 6:20 AM, Tatsuo Ishii <
> ishii at postgresql.org>
> >> >>> wrote:
> >> >>> >
> >> >>> >> I suspect there's some portablity issue with load balance code.
> The
> >> >>> >> actual source code is in select_load_balancing_nodechild.c).
> >> >>> >> Please modify source code and connect to pgpool by using psql.
> >> >>> >> Please send the log output.
> >> >>> >> --
> >> >>> >> Tatsuo Ishii
> >> >>> >> SRA OSS, Inc. Japan
> >> >>> >> English: http://www.sraoss.co.jp/index_en.php
> >> >>> >> Japanese: http://www.sraoss.co.jp
> >> >>> >>
> >> >>> >> int select_load_balancing_node(void)
> >> >>> >> {
> >> >>> >> int selected_slot;
> >> >>> >> double total_weight,r;
> >> >>> >> int i;
> >> >>> >>
> >> >>> >> /* choose a backend in random manner with weight */
> >> >>> >> selected_slot = MASTER_NODE_ID;
> >> >>> >> total_weight = 0.0;
> >> >>> >>
> >> >>> >> for (i=0;i<NUM_BACKENDS;i++)
> >> >>> >> {
> >> >>> >> if (VALID_BACKEND(i))
> >> >>> >> {
> >> >>> >> total_weight +=
> >> BACKEND_INFO(i).backend_weight;
> >> >>> >> }
> >> >>> >> }
> >> >>> >> r = (((double)random())/RAND_MAX) * total_weight;
> >> >>> >> pool_log("r: %f total_weight: %f", r, total_weight);
> >> >>> <--
> >> >>> >> add this
> >> >>> >>
> >> >>> >> total_weight = 0.0;
> >> >>> >> for (i=0;i<NUM_BACKENDS;i++)
> >> >>> >> {
> >> >>> >> if (VALID_BACKEND(i) &&
> >> BACKEND_INFO(i).backend_weight >
> >> >>> >> 0.0)
> >> >>> >> {
> >> >>> >> if(r >= total_weight)
> >> >>> >> selected_slot = i;
> >> >>> >> else
> >> >>> >> break;
> >> >>> >> total_weight +=
> >> BACKEND_INFO(i).backend_weight;
> >> >>> >> }
> >> >>> >> }
> >> >>> >>
> >> >>> >> pool_debug("select_load_balancing_node: selected backend
> id
> >> is
> >> >>> %d",
> >> >>> >> selected_slot);
> >> >>> >> return selected_slot;
> >> >>> >> }
> >> >>> >>
> >> >>> >>
> >> >>> >> > Hi Tatsuo, Thanks for the reply.
> >> >>> >> >
> >> >>> >> > The normalized weights are 0.5 for both nodes and the selected
> >> node is
> >> >>> >> always the same node. I hope then it's srandom().
> >> >>> >> >
> >> >>> >> >
> >> >>> >> > Any idea to solve this srandom issue
> >> >>> >> >
> >> >>> >> >
> >> >>> >> > Thanks and Regards,
> >> >>> >> > Aravinth
> >> >>> >> >
> >> >>> >> >
> >> >>> >> > ________________________________
> >> >>> >> > From: Tatsuo Ishii <ishii at postgresql.org>
> >> >>> >> > To: aravinth at mafiree.com
> >> >>> >> > Cc: pgpool-general at pgpool.net
> >> >>> >> > Sent: Tuesday, May 1, 2012 4:41 AM
> >> >>> >> > Subject: Re: [pgpool-general: 396] strange load balancing
> issue in
> >> >>> >> Solaris
> >> >>> >> >
> >> >>> >> > First of all please check "normalized" weights are as you
> >> expected.
> >> >>> >> > Run "show pool_status;" and see "backend_weight0",
> >> "backend_weight1"
> >> >>> >> > section. You see a floating point numbers, which are the
> >> normalized
> >> >>> >> > weight between 0.0 and 1.0. If you see both are 0.5, primary
> and
> >> >>> >> > standby are given same weight.
> >> >>> >> >
> >> >>> >> > If they are ok, I suspect srandom() function behavior is
> different
> >> >>> >> > from other platforms. Pgpool-II chooses the load balance node
> by
> >> using
> >> >>> >> > srandom(). select_load_balancing_node() is the function which
> is
> >> >>> >> > responsible for selecting the load balance node. If you run
> >> pgpool-II
> >> >>> >> > with -d (debug) option, you will see following in the log:
> >> >>> >> >
> >> >>> >> > pool_debug("select_load_balancing_node: selected backend
> id is
> >> >>> %d",
> >> >>> >> selected_slot);
> >> >>> >> >
> >> >>> >> > If backend_weight in show pool_status are fine but the line
> above
> >> >>> >> > always shows same number, it is the sign that we have problem
> with
> >> >>> >> > srandom().
> >> >>> >> > --
> >> >>> >> > Tatsuo Ishii
> >> >>> >> > SRA OSS, Inc. Japan
> >> >>> >> > English: http://www.sraoss.co.jp/index_en.php
> >> >>> >> > Japanese: http://www.sraoss.co.jp
> >> >>> >> >
> >> >>> >> >> Hi All,
> >> >>> >> >>
> >> >>> >> >> I am facing a strange issue in load balancing with replication
> >> mode
> >> >>> set
> >> >>> >> to
> >> >>> >> >> true in Solaris. Load balancing algorithm always select the
> same
> >> node
> >> >>> >> >> whatever may be the backend weight
> >> >>> >> >>
> >> >>> >> >> Here is the scenario.
> >> >>> >> >>
> >> >>> >> >> I have a pgpool installed installed in 1 server
> >> >>> >> >> 2 postgres nodes in other 2 servers
> >> >>> >> >> replication mode set to true and load balancing set to true
> >> >>> >> >> backend weight of the 2 nodes is 1.
> >> >>> >> >>
> >> >>> >> >> When I fire the queries manuall using different connections or
> >> using
> >> >>> >> >> pgbench all the queries hit the same node. Load balancing
> >> algorithm
> >> >>> >> always
> >> >>> >> >> select the same node.
> >> >>> >> >> No effect in changing the backend weight. Only when I set
> backend
> >> >>> >> weight to
> >> >>> >> >> 0 hits go to the other server.
> >> >>> >> >>
> >> >>> >> >>
> >> >>> >> >> I face this issue only in solaris. The same setup in other
> >> servers (
> >> >>> >> centos
> >> >>> >> >> ,RHEL, ubunt etc) does the load balancing perfectly.
> >> >>> >> >>
> >> >>> >> >> Also tries various postgres versions and pgpool version with
> same
> >> >>> >> result.
> >> >>> >> >> But every version runs fine in other servers.
> >> >>> >> >>
> >> >>> >> >> Has anyone faced this issue?
> >> >>> >> >>
> >> >>> >> >> Any information would highly helpful.
> >> >>> >> >>
> >> >>> >> >> Regards,
> >> >>> >> >> Aravinth
> >> >>> >> _______________________________________________
> >> >>> >> pgpool-general mailing list
> >> >>> >> pgpool-general at pgpool.net
> >> >>> >> http://www.pgpool.net/mailman/listinfo/pgpool-general
> >> >>> >>
> >> >>>
> >> > _______________________________________________
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> >>
>
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