Setting Up Database Monitoring for self hosted Postgres

Setting Up Database Monitoring for self hosted Postgres

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Database Monitoring provides deep visibility into your Postgres databases by exposing query metrics, query samples, explain plans, database states, failovers, and events.

The Agent collects telemetry directly from the database by logging in as a read-only user. Do the following setup to enable Database Monitoring with your Postgres database:

  1. Configure database parameters
  2. Grant the Agent access to the database
  3. Install the Agent

Before you begin

Supported PostgreSQL versions
9.6, 10, 11, 12, 13
Supported Agent versions
7.30.0+
Performance impact
The default Agent configuration for Database Monitoring is conservative, but you can adjust settings such as the collection interval and query sampling rate to better suit your needs. For most workloads, the Agent represents less than one percent of query execution time on the database and less than one percent of CPU.

Database Monitoring runs as an integration on top of the base Agent (see benchmarks).
Proxies, load balancers, and connection poolers
The Agent must connect directly to the host being monitored. For self-hosted databases, 127.0.0.1 or the socket is preferred. The Agent should not connect to the database through a proxy, load balancer, or connection pooler such as pgbouncer. While this can be an anti-pattern for client applications, each Agent must have knowledge of the underlying hostname and should stick to a single host for its lifetime, even in cases of failover. If the Datadog Agent connects to different hosts while it is running, the values of metrics will be incorrect.
Data security considerations
See Sensitive information for information about what data the Agent collects from your databases and how to ensure it is secure.

Configure Postgres settings

Configure the following parameters in the postgresql.conf file and then restart the server for the settings to take effect. For more information about these parameters, see the Postgres documentation.

ParameterValueDescription
shared_preload_librariespg_stat_statementsRequired for postgresql.queries.* metrics. Enables collection of query metrics via the the pg_stat_statements extension.
track_activity_query_size4096Required for collection of larger queries. Increases the size of SQL text in pg_stat_activity and pg_stat_statements. If left at the default value then queries longer than 1024 characters will not be collected.
pg_stat_statements.trackALLOptional. Enables tracking of statements within stored procedures and functions.
pg_stat_statements.max10000Optional. Increases the number of normalized queries tracked in pg_stat_statements. This setting is recommended for high-volume databases that see many different types of queries from many different clients.

Grant the Agent access

The Datadog Agent requires read-only access to the database server in order to collect statistics and queries.

Choose a PostgreSQL database on the database server to which the Agent will connect. The Agent can collect telemetry from all databases on the database server regardless of which one it connects to, so a good option is to use the default postgres database. Choose a different database only if you need the Agent to run custom queries against data unique to that database.

Connect to the chosen database as a superuser (or another user with sufficient permissions). For example, if your chosen database is postgres, connect as the postgres user using psql by running:

psql -h mydb.example.com -d postgres -U postgres

Create the datadog user:

CREATE USER datadog WITH password '<PASSWORD>';

Create the following schema in every database:

CREATE SCHEMA datadog;
GRANT USAGE ON SCHEMA datadog TO datadog;
GRANT USAGE ON SCHEMA public TO datadog;
GRANT pg_monitor TO datadog;
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

Create the following schema in every database:

CREATE SCHEMA datadog;
GRANT USAGE ON SCHEMA datadog TO datadog;
GRANT USAGE ON SCHEMA public TO datadog;
GRANT SELECT ON pg_stat_database TO datadog;
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

Create functions in every database to enable the Agent to read the full contents of pg_stat_activity and pg_stat_statements:

CREATE OR REPLACE FUNCTION datadog.pg_stat_activity() RETURNS SETOF pg_stat_activity AS
  $$ SELECT * FROM pg_catalog.pg_stat_activity; $$
LANGUAGE sql
SECURITY DEFINER;
CREATE OR REPLACE FUNCTION datadog.pg_stat_statements() RETURNS SETOF pg_stat_statements AS
    $$ SELECT * FROM pg_stat_statements; $$
LANGUAGE sql
SECURITY DEFINER;

Note: When generating custom metrics that require querying additional tables, you may need to grant the SELECT permission on those tables to the datadog user. Example: grant SELECT on <TABLE_NAME> to datadog;. See PostgreSQL custom metric collection explained for more information.

Create the function in every database to enable the Agent to collect explain plans.

CREATE OR REPLACE FUNCTION datadog.explain_statement (
   l_query text,
   out explain JSON
)
RETURNS SETOF JSON AS
$$
BEGIN
   RETURN QUERY EXECUTE 'EXPLAIN (FORMAT JSON) ' || l_query;
END;
$$
LANGUAGE 'plpgsql'
RETURNS NULL ON NULL INPUT
SECURITY DEFINER;

Verify

To verify the permissions are correct, run the following commands to confirm the Agent user is able to connect to the database and read the core tables:

psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_database limit 1;" \
  && echo -e "\e[0;32mPostgres connection - OK\e[0m" \
  || echo -e "\e[0;31mCannot connect to Postgres\e[0m"
psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_activity limit 1;" \
  && echo -e "\e[0;32mPostgres pg_stat_activity read OK\e[0m" \
  || echo -e "\e[0;31mCannot read from pg_stat_activity\e[0m"
psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_statements limit 1;" \
  && echo -e "\e[0;32mPostgres pg_stat_statements read OK\e[0m" \
  || echo -e "\e[0;31mCannot read from pg_stat_statements\e[0m"
psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_database limit 1;" \
  && echo -e "\e[0;32mPostgres connection - OK\e[0m" \
  || echo -e "\e[0;31mCannot connect to Postgres\e[0m"
psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_activity limit 1;" \
  && echo -e "\e[0;32mPostgres pg_stat_activity read OK\e[0m" \
  || echo -e "\e[0;31mCannot read from pg_stat_activity\e[0m"
psql -h localhost -U datadog postgres -A \
  -c "select * from pg_stat_statements limit 1;" \
  && echo -e "\e[0;32mPostgres pg_stat_statements read OK\e[0m" \
  || echo -e "\e[0;31mCannot read from pg_stat_statements\e[0m"

When it prompts for a password, use the password you entered when you created the datadog user.

Install the Agent

Installing the Datadog Agent also installs the Postgres check which is required for Database Monitoring on Postgres. If you haven’t already installed the Agent for your Postgres database host, see the Agent installation instructions.

  1. Edit the Agent’s conf.d/postgres.d/conf.yaml file to point to your host / port and set the hosts to monitor. See the sample postgres.d/conf.yaml for all available configuration options.
init_config:
instances:
  - dbm: true
    host: localhost
    port: 5432
    username: datadog
    password: '<PASSWORD>'
    ## Optional: Connect to a different database if needed for `custom_queries`
    # dbname: '<DB_NAME>'
init_config:
instances:
  - dbm: true
    host: localhost
    port: 5432
    username: datadog
    password: '<PASSWORD>'
    pg_stat_statements_view: datadog.pg_stat_statements()
    pg_stat_activity_view: datadog.pg_stat_activity()
    ## Optional: Connect to a different database if needed for `custom_queries`
    # dbname: '<DB_NAME>'
  1. Restart the Agent.

Collecting logs (optional)

PostgreSQL default logging is to stderr, and logs do not include detailed information. It is recommended to log into a file with additional details specified in the log line prefix. Refer to the PostgreSQL documentation on this topic for additional details.

  1. Logging is configured within the file /etc/postgresql/<VERSION>/main/postgresql.conf. For regular log results, including statement outputs, uncomment the following parameters in the log section:
      logging_collector = on
      log_directory = 'pg_log'  # directory where log files are written,
                                # can be absolute or relative to PGDATA
      log_filename = 'pg.log'   # log file name, can include pattern
      log_statement = 'all'     # log all queries
      #log_duration = on
      log_line_prefix= '%m [%p] %d %a %u %h %c '
      log_file_mode = 0644
      ## For Windows
      #log_destination = 'eventlog'
    
  2. To gather detailed duration metrics and make them searchable in the Datadog interface, they should be configured inline with the statement themselves. See below for the recommended configuration differences from above and note that both log_statement and log_duration options are commented out. See discussion on this topic here.

This config logs all statements, but to reduce the output to those which have a certain duration, set the log_min_duration_statement value to the desired minimum duration in milliseconds (check that logging the full SQL statement complies with your organization’s privacy requirements):

  log_min_duration_statement = 0    # -1 is disabled, 0 logs all statements
                                    # and their durations, > 0 logs only
                                    # statements running at least this number
                                    # of milliseconds
  #log_statement = 'all'
  #log_duration = on
  1. Collecting logs is disabled by default in the Datadog Agent, enable it in your datadog.yaml file:
    logs_enabled: true
    
  2. Add and edit this configuration block to your conf.d/postgres.d/conf.yaml file to start collecting your PostgreSQL logs:
    logs:
      - type: file
        path: "<LOG_FILE_PATH>"
        source: postgresql
        service: "<SERVICE_NAME>"
        #To handle multi line that starts with yyyy-mm-dd use the following pattern
        #log_processing_rules:
        #  - type: multi_line
        #    pattern: \d{4}\-(0?[1-9]|1[012])\-(0?[1-9]|[12][0-9]|3[01])
        #    name: new_log_start_with_date
    

    Change the service and path parameter values to configure for your environment. See the sample postgres.d/conf.yaml for all available configuration options.

  3. Restart the Agent.

Validate

Run the Agent’s status subcommand and look for postgres under the Checks section. Or visit the Databases page to get started!

Troubleshooting

If you have installed and configured the integrations and Agent as described and it is not working as expected, see Troubleshooting

Further reading

Additional helpful documentation, links, and articles: