Re: High context switches occurring - Mailing list pgsql-performance

Re-ran it 3 times on each host - 
 
Sun:
-bash-3.00$ time pgbench -s 10 -c 10 -t 3000 pgbench
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
number of clients: 10
number of transactions per client: 3000
number of transactions actually processed: 30000/30000
tps = 827.810778 (including connections establishing)
tps = 828.410801 (excluding connections establishing)
real    0m36.579s
user    0m1.222s
sys     0m3.422s

Intel:
-bash-3.00$ time pgbench -s 10 -c 10 -t 3000 pgbench
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 1
number of clients: 10
number of transactions per client: 3000
number of transactions actually processed: 30000/30000
tps = 597.067503 (including connections establishing)
tps = 597.606169 (excluding connections establishing)
real    0m50.380s
user    0m2.621s
sys     0m7.818s

Thanks,
Anjan
 

    -----Original Message----- 
    From: Anjan Dave 
    Sent: Wed 12/7/2005 10:54 AM 
    To: Tom Lane 
    Cc: Vivek Khera; Postgresql Performance 
    Subject: Re: [PERFORM] High context switches occurring 
    
    

    Thanks for your inputs, Tom. I was going after high concurrent clients, 
    but should have read this carefully - 

    -s scaling_factor 
                    this should be used with -i (initialize) option. 
                    number of tuples generated will be multiple of the 
                    scaling factor. For example, -s 100 will imply 10M 
                    (10,000,000) tuples in the accounts table. 
                    default is 1.  NOTE: scaling factor should be at least 
                    as large as the largest number of clients you intend 
                    to test; else you'll mostly be measuring update 
    contention. 

    I'll rerun the tests. 

    Thanks, 
    Anjan 


    -----Original Message----- 
    From: Tom Lane [mailto:tgl@sss.pgh.pa.us] 
    Sent: Tuesday, December 06, 2005 6:45 PM 
    To: Anjan Dave 
    Cc: Vivek Khera; Postgresql Performance 
    Subject: Re: [PERFORM] High context switches occurring 

    "Anjan Dave" <adave@vantage.com> writes: 
    > -bash-3.00$ time pgbench -c 1000 -t 30 pgbench 
    > starting vacuum...end. 
    > transaction type: TPC-B (sort of) 
    > scaling factor: 1 
    > number of clients: 1000 
    > number of transactions per client: 30 
    > number of transactions actually processed: 30000/30000 
    > tps = 45.871234 (including connections establishing) 
    > tps = 46.092629 (excluding connections establishing) 

    I can hardly think of a worse way to run pgbench :-(.  These numbers are 
    about meaningless, for two reasons: 

    1. You don't want number of clients (-c) much higher than scaling factor 
    (-s in the initialization step).  The number of rows in the "branches" 
    table will equal -s, and since every transaction updates one 
    randomly-chosen "branches" row, you will be measuring mostly row-update 
    contention overhead if there's more concurrent transactions than there 
    are rows.  In the case -s 1, which is what you've got here, there is no 
    actual concurrency at all --- all the transactions stack up on the 
    single branches row. 

    2. Running a small number of transactions per client means that 
    startup/shutdown transients overwhelm the steady-state data.  You should 
    probably run at least a thousand transactions per client if you want 
    repeatable numbers. 

    Try something like "-s 10 -c 10 -t 3000" to get numbers reflecting test 
    conditions more like what the TPC council had in mind when they designed 
    this benchmark.  I tend to repeat such a test 3 times to see if the 
    numbers are repeatable, and quote the middle TPS number as long as 
    they're not too far apart. 

                            regards, tom lane 


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