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Full Discussion: Disk Performance
Operating Systems Linux Disk Performance Post 302961567 by jimthompson on Tuesday 1st of December 2015 10:28:34 AM
Old 12-01-2015
Disk Performance

I have a freshly installed Oracle Linux 7.1 ( akin to RHEL ) server.

However after installing some Oracle software, I have noticed that my hard disk light is continually on and the system performance is slow.

So I check out SAR and IOSTAT

Code:
lab3:/root>iostat
Linux 3.8.13-55.1.6.el7uek.x86_64 (lab3)        01/12/15        _x86_64_        (2 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
          21.33    0.00    2.66   41.71    0.00   34.30

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
sda             100.94      1928.77       653.97  110966874   37624674
sdb              53.08       929.61      3510.79   53482763  201984646
dm-0            438.70      1351.24       653.67   77740019   37607217
dm-1              0.01         0.02         0.00       1396          0
dm-2              4.93       577.01         0.27   33196938      15409

lab3:/root>sar 5 5
Linux 3.8.13-55.1.6.el7uek.x86_64 (lab3)        01/12/15        _x86_64_        (2 CPU)

15:19:06        CPU     %user     %nice   %system   %iowait    %steal     %idle
15:19:11        all      0.50      0.00      0.40      3.52      0.00     95.58
15:19:16        all      0.50      0.00      0.50      2.21      0.00     96.78
15:19:21        all      0.70      0.00      0.40      1.81      0.00     97.08
15:19:26        all      0.40      0.00      0.40      3.73      0.00     95.46
15:19:31        all      0.50      0.00      0.50     13.29      0.00     85.70
Average:        all      0.52      0.00      0.44      4.91      0.00     94.12

Now I only have 2 disks in my server i.e. /dev/sda and /dev/sdb

Q1. Why does Linux create dm-0,dm-1 and dm-2 as separate devices ( albeit I guess these are virtual devices via Device Manager ?
As far as I can tell these are the Oracle Linux Home, the Swap Device and
the Oracle Linux Root - however Idon't see a command directly linking dm-0, and dm-1 which the /home and / mount points

Q2. How do you tell if the dm-0, dm-1 and dm-2 are using the sda or sdb device ?

Q3. I see dm-0 ( Linux Home ) is experiencing a high rate of tps ( transactions per second ? ) whereas the sda device ( which I believe dm-0 is ultamately on ) is experiencing a high amount of data read - is this where my performance problem resides ?

Q4. Is there a way to tell which mounted file system is performing poorly ?

Q5. Why when I increase the Swap from 3 Gb to 19 Gb, I do this by adding a swap file ? Why is the 3 Gb shown as a swap device but the additional 16 Gb is not shown as a device ?

Code:
lab3:/root>swapon
NAME       TYPE      SIZE USED PRIO
/swapfile1 file       16G 6.8G   -1
/dev/dm-1  partition   3G   0B   -2

any help greatly appreciated
Jim

Last edited by Scrutinizer; 12-01-2015 at 12:18 PM.. Reason: Code tags
 

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OCI_SET_ACTION(3)														 OCI_SET_ACTION(3)

oci_set_action - Sets the action name

SYNOPSIS
bool oci_set_action (resource $connection, string $action_name) DESCRIPTION
Sets the action name for Oracle tracing. The action name is registered with the database when the next 'roundtrip' from PHP to the database occurs, typically when an SQL statement is executed. The action name can subsequently be queried from database administration views such as V$SESSION. It can be used for tracing and monitor- ing such as with V$SQLAREA and DBMS_MONITOR.SERV_MOD_ACT_STAT_ENABLE. The value may be retained across persistent connections. PARAMETERS
o $connection -An Oracle connection identifier, returned by oci_connect(3), oci_pconnect(3), or oci_new_connect(3). o $action_name - User chosen string up to 32 bytes long. RETURN VALUES
Returns TRUE on success or FALSE on failure. EXAMPLES
Example #1 Setting the action <?php $c = oci_connect('hr', 'welcome', 'localhost/XE'); // Record the action oci_set_action($c, 'Friend Lookup'); // Code that causes a roundtrip, for example a query: $s = oci_parse($c, 'select * from dual'); oci_execute($s); oci_fetch_all($s, $res); sleep(30); ?> // While the script is running, the administrator can see the actions // being performed: sqlplus system/welcome SQL> select action from v$session; NOTES
Note Oracle version requirement This function is available when PHP is linked with Oracle Database libraries from version 10 g onwards. Tip Performance With older versions of OCI8 or the Oracle Database, the client information can be set using the Oracle DBMS_APPLICATION_INFO pack- age. This is less efficient than using oci_set_client_info(3). Caution Roundtrip Gotcha Some but not all OCI8 functions cause roundtrips. Roundtrips to the database may not occur with queries when result caching is enabled. SEE ALSO
oci_set_module_name(3), oci_set_client_info(3), oci_set_client_identifier(3). PHP Documentation Group OCI_SET_ACTION(3)
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