Performance Analysis and Tuning v13

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Advanced Server provides various tools for performance analysis and tuning. These features are described in this section.

Dynatune

Advanced Server supports dynamic tuning of the database server to make the optimal usage of the system resources available on the host machine on which it is installed. The two parameters that control this functionality are located in the postgresql.conf file. These parameters are:

  • edb_dynatune
  • edb_dynatune_profile

edb_dynatune

edb_dynatune determines how much of the host system's resources are to be used by the database server based upon the host machine's total available resources and the intended usage of the host machine.

When Advanced Server is initially installed, the edb_dynatune parameter is set in accordance with the selected usage of the host machine on which it was installed - i.e., development machine, mixed use machine, or dedicated server. For most purposes, there is no need for the database administrator to adjust the various configuration parameters in the postgresql.conf file in order to improve performance.

You can change the value of the edb_dynatune parameter after the initial installation of Advanced Server by editing the postgresql.conf file. The postmaster must be restarted in order for the new configuration to take effect.

The edb_dynatune parameter can be set to any integer value between 0 and 100, inclusive. A value of 0, turns off the dynamic tuning feature thereby leaving the database server resource usage totally under the control of the other configuration parameters in the postgresql.conf file.

A low non-zero, value (e.g., 1 - 33) dedicates the least amount of the host machine's resources to the database server. This setting would be used for a development machine where many other applications are being used.

A value in the range of 34 - 66 dedicates a moderate amount of resources to the database server. This setting might be used for a dedicated application server that may have a fixed number of other applications running on the same machine as Advanced Server.

The highest values (e.g., 67 - 100) dedicate most of the server's resources to the database server. This setting would be used for a host machine that is totally dedicated to running Advanced Server.

Once a value of edb_dynatune is selected, database server performance can be further fine-tuned by adjusting the other configuration parameters in the postgresql.conf file. Any adjusted setting overrides the corresponding value chosen by edb_dynatune. You can change the value of a parameter by un-commenting the configuration parameter, specifying the desired value, and restarting the database server.

edb_dynatune_profile

The edb_dynatune_profile parameter is used to control tuning aspects based upon the expected workload profile on the database server. This parameter takes effect upon startup of the database server.

The possible values for edb_dynatune_profile are:

ValueUsage
oltpRecommended when the database server is processing heavy online transaction processing workloads.
reportingRecommended for database servers used for heavy data reporting.
mixedRecommended for servers that provide a mix of transaction processing and data reporting.

EDB Wait States

The EDB wait states contrib module contains two main components.

EDB Wait States Background Worker (EWSBW)

When the wait states background worker is registered as one of the shared preload libraries, EWSBW probes each of the running sessions at regular intervals.

For every session it collects information such as the database to which it is connected, the logged in user of the session, the query running in that session, and the wait events on which it is waiting.

This information is saved in a set of files in a user-configurable path and directory folder given by the edb_wait_states.directory parameter to be added to the postgresql.conf file. The specified path must be a full, absolute path and not a relative path.

The following describes the installation process on a Linux system.

Step 1: EDB wait states is installed with the edb-asxx-server-edb-modules RPM package where xx is the Advanced Server version number.

Step 2: To launch the worker, it must be registered in the postgresql.conf file using the shared_preload_libraries parameter, for example:

shared_preload_libraries = '$libdir/edb_wait_states'

Step 3: Restart the database server. After a successful restart, the background worker begins collecting data.

Step 4: To review the data, create the following extension:

CREATE EXTENSION edb_wait_states;

Step 5: To terminate the EDB wait states worker, remove $libdir/edb_wait_states from the shared_preload_libraries parameter and restart the database server.

The following describes the installation process on a Windows system.

Step 1: EDB wait states module is installed with the EDB Modules installer by invoking StackBuilder Plus utility. Follow the onscreen instructions to complete the installation of the EDB Modules.

Step 2: To register the worker, modify the postgresql.conf file to include the wait states library in the shared_preload_libraries configuration parameter. The parameter value must include:

shared_preload_libraries = '$libdir/edb_wait_states.dll'

The EDB wait states installation places the edb_wait_states.dll library file in the following path:

C:\Program Files\edb\as13\lib\

Step 3: Restart the database server for the changes to take effect. After a successful restart, the background worker gets started and starts collecting the data.

Step 4: To view the data, create the following extension:

CREATE EXTENSION edb_wait_states;

The installer places the edb_wait_states.control file in the following path:

C:\Program Files\edb\as13\share\extension

Terminating the Wait States Worker

To terminate the EDB wait states worker, use the DROP EXTENSION command to drop the edb_wait_states extension; then modify the postgresql.conf file, removing $libdir/edb_wait_states.dll from the shared_preload_libraries parameter. Restart the database server after modifying the postgresql.conf file to apply your changes.

The Wait States Interface

The interface includes the functions listed in the following sections. Each of these functions has common input and output parameters. Those parameters are as follows:

  • start_ts and end_ts (IN). Together these specify the time interval and the data within which is to be read. If only start_ts is specified, the data starting from start_ts is output. If only end_ts is provided, data up to end_ts is output. If none of those are provided, all the data is output. Every function outputs different data. The output of each function will be explained below.
  • query_id (OUT). Identifies a normalized query. It is internal hash code computed from the query.
  • session_id (OUT). Identifies a session.
  • ref_start_ts and ref_end_ts (OUT). Provide the timestamps of a file containing a particular data point. A data point may be a wait event sample record or a query record or a session record.

The syntax of each function is given in the following sections.

Note

The examples shown in the following sections are based on the following three queries executed on four different sessions connected to different databases using different users, simultaneously:

SELECT schemaname FROM pg_tables, pg_sleep(15) WHERE schemaname <>
'pg_catalog'; /* ran on 2 sessions */
SELECT tablename FROM pg_tables, pg_sleep(10) WHERE schemaname <>
'pg_catalog';
SELECT tablename, schemaname FROM pg_tables, pg_sleep(10) WHERE schemaname
<> 'pg_catalog';

edb_wait_states_data

This function is used to read the data collected by EWSBW.

edb_wait_states_data(
  IN start_ts timestamptz default '-infinity'::timestamptz,
  IN end_ts timestamptz default 'infinity'::timestamptz,
  OUT session_id int4,
  OUT <dbname> text,
  OUT <username> text,
  OUT <query> text,
  OUT <query_start_time> timestamptz,
  OUT <sample_time> timestamptz,
  OUT <wait_event_type> text,
  OUT <wait_event> text
)

This function can be used to find out the following:

The queries running in the given duration (defined by start_ts and end_ts) in all the sessions, and the wait events, if any, they were waiting on. For example:

SELECT query, session_id, wait_event_type, wait_event
  FROM edb_wait_states_data(start_ts, end_ts);

The progress of a session within a given duration (that is, the queries run in a session (session_id = 100000) and the wait events the queries waited on). For example:

SELECT query, wait_event_type, wait_event
  FROM edb_wait_states_data(start_ts, end_ts)
  WHERE session_id = 100000;

The duration for which the samples are available. For example:

SELECT min(sample_time), max(sample_time)
  FROM edb_wait_states_data();

Parameters

In addition to the common parameters described previously, each row of the output gives the following:

dbname

The session's database

username

The session's logged in user

query

The query running in the session

query_start_time

The time when .the query started

sample_time

The time when wait event data was collected

wait_event_type

The type of wait event the session (backend) is waiting on

wait_event

The wait event the session (backend) is waiting on

Example

The following is a sample output from the edb_wait_states_data() function.

edb=# SELECT * FROM edb_wait_states_data();
-[ RECORD 1 ]----+-------------------------------------------------------------------------
session_id       | 4398
dbname           | edb
username         | enterprisedb
query            | SELECT schemaname FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
query_start_time | 17-AUG-18 11:56:05.271962 -04:00
sample_time      | 17-AUG-18 11:56:19.700236 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
-[ RECORD 2 ]----+-------------------------------------------------------------------------
session_id       | 4398
dbname           | edb
username         | enterprisedb
query            | SELECT schemaname FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
query_start_time | 17-AUG-18 11:56:05.271962 -04:00
sample_time      | 17-AUG-18 11:56:18.699938 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
-[ RECORD 3 ]----+-------------------------------------------------------------------------
session_id       | 4398
dbname           | edb
username         | enterprisedb
query            | SELECT schemaname FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
query_start_time | 17-AUG-18 11:56:05.271962 -04:00
sample_time      | 17-AUG-18 11:56:17.700253 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
                    .
                    .
                    .

edb_wait_states_queries

This function gives information about the queries sampled by EWSBW.

edb_wait_states_queries(
  IN start_ts timestamptz default '-infinity'::timestamptz,
  IN end_ts timestamptz default 'infinity'::timestamptz,
  OUT query_id int8,
  OUT <query> text,
  OUT ref_start_ts timestamptz
  OUT ref_end_ts timestamptz
)

A new queries file is created periodically and thus, there can be multiple query files generated corresponding to specific intervals.

This function returns all the queries in query files that overlap with the given time interval. A query as shown below, gives all the queries in query files that contained queries sampled between start_ts and end_ts.

In other words, the function may output queries that did not run in the given interval. To exactly know that the user should use edb_wait_states_data().

SELECT query FROM edb_wait_states_queries(start_ts, end_ts);

Parameters

In addition to the common parameters described previously, each row of the output gives the following:

query

Normalized query text

Example

The following is a sample output from the edb_wait_states_queries() function.

edb=# SELECT * FROM edb_wait_states_queries();
-[ RECORD 1 ]+-----------------------------------------------------------------------------
query_id     | 4292540138852956818
query        | SELECT schemaname FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00
-[ RECORD 2 ]+-----------------------------------------------------------------------------
query_id     | 3754591102365859187
query        | SELECT tablename FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00
-[ RECORD 3 ]+-----------------------------------------------------------------------------
query_id     | 349089096300352897
query        | SELECT tablename, schemaname FROM pg_tables, pg_sleep($1) WHERE schemaname <> $2
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00

edb_wait_states_sessions

This function gives information about the sessions sampled by EWSBW.

edb_wait_states_sessions(
  IN start_ts timestamptz default '-infinity'::timestamptz,
  IN end_ts timestamptz default 'infinity'::timestamptz,
  OUT session_id int4,
  OUT <dbname> text,
  OUT <username> text,
  OUT ref_start_ts timestamptz
  OUT ref_end_ts timestamptz
)

This function can be used to identify the databases that were connected and/or which users started those sessions. For example:

SELECT dbname, username, session_id
  FROM edb_wait_states_sessions();

Similar to edb_wait_states_queries(), this function outputs all the sessions logged in session files that contain sessions sampled within the given interval and not necessarily only the sessions sampled within the given interval. To identify that one should use edb_wait_states_data().

Parameters

In addition to the common parameters described previously, each row of the output gives the following:

dbname

The database to which the session is connected

username

Login user of the session

Example

The following is a sample output from the edb_wait_states_sessions() function.

edb=# SELECT * FROM edb_wait_states_sessions();
-[ RECORD 1 ]+---------------------------------
session_id   | 4340
dbname       | edb
username     | enterprisedb
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00
-[ RECORD 2 ]+---------------------------------
session_id   | 4398
dbname       | edb
username     | enterprisedb
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00
-[ RECORD 3 ]+---------------------------------
session_id   | 4410
dbname       | db1
username     | user1
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00
-[ RECORD 4 ]+---------------------------------
session_id   | 4422
dbname       | db2
username     | user2
ref_start_ts | 17-AUG-18 11:52:38.698793 -04:00
ref_end_ts   | 18-AUG-18 11:52:38.698793 -04:00

edb_wait_states_samples

This function gives information about wait events sampled by EWSBW.

edb_wait_states_samples(
  IN start_ts timestamptz default '-infinity'::timestamptz,
  IN end_ts timestamptz default 'infinity'::timestamptz,
  OUT query_id int8,
  OUT session_id int4,
  OUT <query_start_time> timestamptz,
  OUT <sample_time> timestamptz,
  OUT <wait_event_type> text,
  OUT <wait_event> text
)

Usually, a user would not be required to call this function directly.

Parameters

In addition to the common parameters described previously, each row of the output gives the following:

query_start_time

The time when the query started in this session

sample_time

The time when wait event data was collected

wait_event_type

The type of wait event on which the session is waiting

wait_event

The wait event on which the session (backend) is waiting

Example

The following is a sample output from the edb_wait_states_samples() function.

edb=# SELECT * FROM edb_wait_states_samples();
-[ RECORD 1 ]----+---------------------------------
query_id         | 4292540138852956818
session_id       | 4340
query_start_time | 17-AUG-18 11:56:00.39421 -04:00
sample_time      | 17-AUG-18 11:56:00.699934 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
-[ RECORD 2 ]----+---------------------------------
query_id         | 4292540138852956818
session_id       | 4340
query_start_time | 17-AUG-18 11:56:00.39421 -04:00
sample_time      | 17-AUG-18 11:56:01.699003 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
-[ RECORD 3 ]----+---------------------------------
query_id         | 4292540138852956818
session_id       | 4340
query_start_time | 17-AUG-18 11:56:00.39421 -04:00
sample_time      | 17-AUG-18 11:56:02.70001 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
-[ RECORD 4 ]----+---------------------------------
query_id         | 4292540138852956818
session_id       | 4340
query_start_time | 17-AUG-18 11:56:00.39421 -04:00
sample_time      | 17-AUG-18 11:56:03.700081 -04:00
wait_event_type  | Timeout
wait_event       | PgSleep
                    .
                    .
                    .

edb_wait_states_purge

The function deletes all the sampled data files (queries, sessions and wait event samples) that were created after start_ts and aged (rotated) before end_ts.

edb_wait_states_purge(
  IN start_ts timestamptz default '-infinity'::timestamptz,
  IN end_ts timestamptz default 'infinity'::timestamptz
)

Usually a user does not need to run this function. The backend should purge those according to the retention age, but in case, that doesn't happen for some reason, this function may be used.

In order to know the duration for which the samples have been retained, use edb_wait_states_data() as explained in the previous examples of that function.

Example

The $PGDATA/edb_wait_states directory before running edb_wait_states_purge():

[root@localhost data]# pwd
/var/lib/edb/as13/data
[root@localhost data]# ls -l edb_wait_states
total 12
-rw------- 1 enterprisedb ...  253 Aug 17 11:56 edb_ws_queries_587836358698793_587922758698793
-rw------- 1 enterprisedb ... 1600 Aug 17 11:56 edb_ws_samples_587836358698793_587839958698793
-rw------- 1 enterprisedb ...   94 Aug 17 11:56 edb_ws_sessions_587836358698793_587922758698793

The $PGDATA/edb_wait_states directory after running edb_wait_states_purge():

edb=# SELECT * FROM edb_wait_states_purge();
 edb_wait_states_purge
-----------------------

(1 row)

[root@localhost data]# pwd
/var/lib/edb/as13/data
[root@localhost data]# ls -l edb_wait_states
total 0