Re: Performances issues with SSD volume ?

> From: Thomas SIMON <tsimon@neteven.com>
>To: Glyn Astill <glynastill@yahoo.co.uk>
>Cc: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
>Sent: Tuesday, 26 May 2015, 15:44
>Subject: Re: [ADMIN] Performances issues with SSD volume ?
>
>I can't do bonnie++ now, beacause I've already prepared server as a
>slave, and I have no sufficient disk space available (program says File
>size should be double RAM for good results output)
>
>My current sar output on productions (HDD) server is:
>14:25:01          DEV                    tps  rd_sec/s  wr_sec/s
>avgrq-sz  avgqu-sz     await     svctm     %util
>
>11:05:01    vg_data-lv_data    954.37   2417.35  18941.77 22.38
>31.10     32.46      0.34     32.70
>11:15:01    vg_data-lv_data   1155.79   8716.91  21995.77 26.57
>25.15     21.74      0.40     46.70
>11:25:01    vg_data-lv_data   1250.62   6478.67  23450.07 23.93
>39.77     31.78      0.41     51.34
>11:35:01    vg_data-lv_data    842.48   2051.11  17120.92 22.76
>15.63     18.53      0.29     24.04
>11:45:01    vg_data-lv_data    666.21   1403.32  14174.47 23.38
>10.11     15.12      0.24     15.79
>11:55:01    vg_data-lv_data    923.51   6763.36  15337.58 23.93
>13.07     14.14      0.35     32.63
>12:05:01    vg_data-lv_data    989.86   9148.71  16252.59 25.66
>19.42     19.56      0.45     44.21
>12:15:01    vg_data-lv_data   1369.24   8631.93  24737.60 24.37
>35.04     25.54      0.45     61.33
>12:25:01    vg_data-lv_data   1776.12   7070.01  39851.34 26.42
>74.81     42.05      0.44     77.29
>12:35:01    vg_data-lv_data   1529.15   6635.80  85865.14 60.49
>54.11     35.34      0.48     72.89
>12:45:01    vg_data-lv_data   1187.43   4528.74  40366.95 37.81
>36.07     30.36      0.39     45.81
>12:55:01    vg_data-lv_data    984.48   3520.06  21539.36 25.45
>17.91     18.17      0.31     30.20
>13:05:01    vg_data-lv_data    926.54   6304.44  16688.94 24.82
>17.36     18.69      0.41     38.05
>13:15:01    vg_data-lv_data   1232.46   7199.65  29852.49 30.06
>40.17     32.53      0.42     51.60
>13:25:01    vg_data-lv_data   1223.46   3945.05  27448.15 25.66
>31.07     25.31      0.35     42.65
>13:35:01    vg_data-lv_data   1126.91   2811.70  22067.19 22.08
>24.33     21.55      0.32     36.00
>13:45:01    vg_data-lv_data    833.33   1805.26  17274.43 22.90
>24.40     29.25      0.30     25.41
>13:55:02    vg_data-lv_data   1085.88   7616.75  19140.67 24.64
>17.48     16.06      0.39     42.15
>14:05:01    vg_data-lv_data    691.52   3852.50  13125.53 24.55
>7.75     11.15      0.30     20.74
>14:15:01    vg_data-lv_data   1288.88   5390.41  24171.07 22.94
>33.31     25.76      0.36     46.31
>14:25:01    vg_data-lv_data   1592.88   3637.77  29836.89 21.02
>76.45     47.94      0.40     63.28
>14:35:01    vg_data-lv_data   1652.78   9502.87  31587.68 24.86
>58.97     35.58      0.44     72.46
>14:45:01    vg_data-lv_data   1623.82   6249.52  34148.46 24.88
>53.47     32.83      0.40     65.19
>14:55:01    vg_data-lv_data   1330.44   6516.11  26828.59 25.06
>55.66     41.81      0.42     55.46
>Average:    vg_data-lv_data   1176.55   5508.02  26324.37 27.06
>33.86     28.72      0.39     45.59


So the i/o is read heavy, it would be interesting to see why that might be and some insight into running queries would
goa long way there.  


>Quick answer on principal values on db
>size ~ 150 GB.
>Standard comportement is 55% update, 40% select & 10 % insert ; around
>170 TPS.
>


Again, if this is a dedicated postgres server I'd be hoping for there to be pretty much 0 reads from disk as your whole
databaseshould fit in os buffer cache.  Only 170 TPS, are these large operations like bulk loads and big selects? 


Can you post the ouput of "free -m" and "cat /proc/meminfo"?