Re: Heavy inserts load wile querying...

On Tue, Jul 24, 2012 at 6:22 AM, Ioannis Anagnostopoulos <ioannis@anatec.com> wrote:

Hello,
The Postres 9.0 database we use gets about 20K inserts per minute. As long as you don't query at the same time the database is copying fine. However long running queries seems to delay so much the db that the application server buffers the incoming data as it cannot insert them fast enough. The server has 4 HD. One is used for archive, past static tables, the second is the index of the current live tables and the third is the current data. The fourth is the OS.

The serve specs are:
Intel(R) Xeon(R) CPU           W3520  @ 2.67GHz
4 cores
18GB Ram

Do you think that this work load is high that requires an upgrade to cluster or RAID 10 to cope with it?

You need to learn more about what exactly is your bottleneck ... memory, CPU, or I/O.  That said, I suspect you'd be way better off with this hardware if you built a single software RAID 10 array and put everything on it.

Right now, the backup disk and the OS disk are sitting idle most of the time.  With a RAID10 array, you'd at least double, maybe quadruple your I/O.  And if you added a battery-backed RAID controller, you'd have a pretty fast system.

Craig
 

Kind Regards
Yiannis

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I can only assume that it is an i/o issue. At last this is what I can read from iostat:


Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00   277.50    0.00   20.00     0.00  2344.00   117.20     0.09    2.25   4.50   9.00
sdb               1.00     0.50  207.50    4.50 45228.00    33.50   213.50     2.40   11.34   4.13  87.50
sdc               0.00     0.00   29.50    0.00  4916.00     0.00   166.64     0.11    3.73   1.36   4.00
sdd               0.00     0.00    4.00  179.50    96.00  3010.00    16.93   141.25  828.77   5.45 100.00

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           7.60    0.00    2.08   46.45    0.00   43.87

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sda               0.00    61.50    0.00   28.00     0.00   704.00    25.14     0.04    3.04   1.43   4.00
sdb               2.00     0.00   90.50  162.00 19560.00  2992.00    89.31    78.92  194.26   3.76  95.00
sdc               0.00     0.00   10.50    0.00  2160.00     0.00   205.71     0.02    1.90   1.90   2.00
sdd               0.00     0.00    1.50  318.50    24.00  5347.00    16.78   134.72  572.81   3.12 100.00

Where sdb is the data disk and sdd is the index disk. "Top" hardly reports anything more than 10% per postgress process ever, while when the query is running, these numbers on iostat are consistatnly high. At least I can identify my buffering the moment that index hits 100% util. Is there any other way that I can identify bottlenecks in a more positive way?