How do you identify high load tables/indexes in Postgres

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To identify high-load tables or indexes in Postgres, you can use the pg_stat_all_tables or pg_stat_all_indexes views. These views provide information about the access statistics for each table and index in a database. To access these views, you can connect to your Postgres database using a tool like psql and then run a query like the following:

SELECT * FROM pg_stat_all_tables;

This will return a list of all tables in the database, along with information about their size, the number of reads and writes performed on the table, and the amount of time spent reading and writing to the table. You can then sort the results by the number of reads or writes to identify the tables that are receiving the most traffic.

For indexes, you can use a similar query to pg_stat_all_indexes:

SELECT * FROM pg_stat_all_indexes;

This will return a list of all indexes in the database, along with information about the number of reads and writes performed on each index, and the amount of time spent reading and writing to the index. You can then sort the results by the number of reads or writes to identify the indexes that are receiving the most traffic.

It’s worth noting that these views only provide information about the activity on the tables and indexes since the last time the database was started. To get a more comprehensive view of the activity on your tables and indexes, you can collect this information over time and analyze it using tools like Graphite or Grafana. This will allow you to see trends and patterns in the usage of your tables and indexes, and identify any potential performance bottlenecks.

How can you find the top 5 most heavily used tables for the last week in a postgres database?

To find the top 5 most heavily used tables in a Postgres database for the last week, you would need to collect usage statistics for each table over time and then analyze the data to identify the tables that received the most traffic. Here are the steps you would need to follow to do this:

  1. First, connect to your Postgres database using a tool like psql.
  2. Next, create a new table to store the usage statistics for each table. You can do this by running a CREATE TABLE statement like the following:

CREATE TABLE table_usage_stats (

    table_name text,

    reads bigint,

    writes bigint,

    read_time double precision,

    write_time double precision,

    date timestamp

);

  1. Next, you need to create a script that will collect the usage statistics for each table in the database and insert them into the table_usage_stats table. You can do this by running a SELECT query against the pg_stat_all_tables view, which provides information about the access statistics for each table in the database. The query might look something like this:

INSERT INTO table_usage_stats (table_name, reads, writes, read_time, write_time, date)

SELECT relname, heap_blks_read, heap_blks_hit, heap_blks_hit * avg_blk_read_time, heap_blks_hit * avg_blk_write_time, NOW()

FROM pg_stat_all_tables;

  1. To collect the usage statistics on a regular basis, you can set up a cron job or use a tool like pg_cron to run the script at regular intervals (e.g. once per hour).
  2. After collecting the usage statistics for a week, you can then query the table_usage_stats table to identify the top 5 most heavily used tables. You can do this by running a SELECT query that uses the SUM function to total the number of reads and writes for each table, and then sorts the results by the total number of reads and writes. The query might look something like this:

SELECT table_name, SUM(reads) + SUM(writes) AS total_activity

FROM table_usage_stats

WHERE date >= NOW() – INTERVAL ‘1 week’

GROUP BY table_name

ORDER BY total_activity DESC

LIMIT 5;

This query will return the names of the top 5 tables that received the most reads and writes over the past week, along with the total number of reads and writes performed on each table.

It’s worth noting that this approach assumes that you are collecting usage statistics for each table on a regular basis and storing them in a dedicated table. If you are not doing this, you would need to modify the steps above to collect the usage statistics for the last week and then analyze them to identify the top 5 most heavily used tables.

Are there any tools that can automate this?

There are tools that can automate the process of collecting usage statistics for tables and indexes in a Postgres database and analyzing the data to identify potential performance bottlenecks. One example of such a tool is pgwatch2, which is an open-source monitoring and alerting tool for Postgres databases.

pgwatch2 can collect a wide range of metrics from a Postgres database, including metrics on table and index usage, and then display the data in easy-to-read charts and graphs. It can also alert you if certain metrics exceed specified thresholds, so you can quickly identify and address any potential performance issues.

To use pgwatch2, you would need to install it on a server that has access to your Postgres database, and then configure it to collect the metrics you are interested in. You can find more information about pgwatch2, including installation instructions, on the project’s GitHub page: https://github.com/cybertec-postgresql/pgwatch2.

There are many other tools that can automate the process of collecting and analyzing usage statistics for tables and indexes in a Postgres database. Some other examples of tools that you could use for this purpose include:

  • pgbadger: pgbadger is an open-source tool that analyzes the log files generated by a Postgres database and generates reports on the database’s activity. It can provide detailed information on the queries that are executed on the database, including the tables and indexes that are used in each query.
  • pgmetrics: pgmetrics is an open-source tool that collects a wide range of metrics from a Postgres database, including metrics on table and index usage. It can display the data in easy-to-read charts and graphs, and can also alert you if certain metrics exceed specified thresholds.
  • pg_activity: pg_activity is an open-source tool that provides a real-time view of the activity on a Postgres database, including information on table and index usage. It can display the data in easy-to-read tables and graphs, and can also alert you if certain metrics exceed specified thresholds.

You can find more information about these and other tools on the Postgres website: https://www.postgresql.org/docs/current/monitoring.html.

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