Oracle IO Latency Test

Functions such as direct reads, direct writes, buffer cache reads, DBWR etc., often generate a high level of I/O activity on the storage sub-system of Oracle. If the Oracle storage is not sized right to handle the I/O load, then one/more of these mission-critical functions may significantly slowdown (i.e., take more than 500 milliseconds to complete), thus delaying critical database operations. In the event of such a slowdown therefore, administrators must be able to quickly and accurately pinpoint the latent function and determine what is ailing that function, so that the configuration of the Oracle server or its storage sub-system can be fine-tuned to avoid such anomalies. This is where the Oracle IO Latency test helps. This test automatically identifies those functions that are taking more than 500 milliseconds to complete. For each of these functions, this test reports the size of the I/O generated by that function and exactly how much time Oracle’s storage sub-system takes to process this I/O load. In the process, the test turns the spotlight on the latent functions and reveals if the high I/O latency is due to a poorly configured storage system.

Target of the test : An Oracle 12c server

Agent deploying the test : An internal agent

Outputs of the test : One set of results for every I/O function that is taking more than 500 milliseconds to complete.

Configurable parameters for the test
  1. TEST PERIOD - How often should the test be executed
  2. Host – The host for which the test is to be configured
  3. Port - The port on which the server is listening
  4. User – In order to monitor an Oracle database server, a special database user account has to be created in every Oracle database instance that requires monitoring. A Click here hyperlink is available in the test configuration page, using which a new oracle database user can be created. Alternatively, you can manually create the special database user. When doing so, ensure that this user is vested with the select_catalog_role and create session privileges.

    The sample script we recommend for user creation (in Oracle database server versions before 12c) for eG monitoring is:

    create user oraeg identified by oraeg

    create role oratest;

    grant create session to oratest;

    grant select_catalog_role to oratest;

    grant oratest to oraeg;

    The sample script we recommend for user creation (in Oracle database server 12c) for eG monitoring is:

    alter session set container=<Oracle_service_name>;

    create user <user_name>identified by <user_password> container=current default tablespace <name_of_default_tablespace> temporary tablespace <name_of_temporary_tablespace>;

    Grant create session to <user_name>;                                

    Grant select_catalog_role to <user_name>;

    The name of this user has to be specified here.

  5. Password – Password of the specified database user

    This login information is required to query Oracle’s internal dynamic views, so as to fetch the current status / health of the various database components.

  6. Confirm password – Confirm the password by retyping it here.
  7. listener name – Specify the Oracle listener name. By default, this will be the same as the Oracle SID.
  8. ISPASSIVE – If the value chosen is yes, then the Oracle server under consideration is a passive server in an Oracle cluster. No alerts will be generated if the server is not running. Measures will be reported as “Not applicable" by the agent if the server is not up.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

IO size:

Indicates the current size of the I/O generated by this function.

Bytes

This is a good indicator of the current I/O workload on the Oracle storage.

IO latency:

Indicate the total I/O latency of this function.

Msecs

Compare the value of this measure across functions to know which function is the most latent.

Average IO latency:

Indicates the average I/O latency of this function.

Msecs

This represents the time taken by the storage sub-system to process a single byte of I/O requests for the function.

A very high value is indicative of the inability of the storage system to process requests for a function quickly. This could be because the storage system is not configured with adequate space. You may want to consider resizing the storage system to ensure better I/O throughput. 

Max IO latency:

Indicates the maximum I/O latency for a single byte of requests for this function.

Msecs

A high value is a cause for concern, as it indicates a potentially latent function.