steve-chavez
79620396ed
* drop unavailable doc pages from release notes * rename releases pages so they order in TOC
84 lines
3.7 KiB
ReStructuredText
84 lines
3.7 KiB
ReStructuredText
Connection Pool
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===============
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Every request to an :doc:`API resource <api>` borrows a connection from the connection pool to start a :doc:`transaction <transactions>`.
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A connection pool is a cache of reusable database connections. It allows serving many HTTP requests using few database connections.
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Minimizing connections it’s paramount to performance. Each PostgreSQL connection creates a process, having too many can exhaust available resources.
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.. _pool_growth_limit:
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Growth Limit
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------------
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If all the connections are being used, a new connection is added to the pool. The pool can grow until it reaches the :ref:`db-pool` size.
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Note it’s pointless to set this higher than the ``max_connections`` setting in your database.
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Connection lifetime
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-------------------
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After a period of time, connections from the pool will be released and news ones will be created. This time is specified by :ref:`db-pool-max-lifetime`.
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The lifetime doesn't affect running requests. Only unused connections will be released.
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For knowing why a connection lifetime is necessary, see the following discussion:
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https://www.postgresql.org/message-id/flat/CA%2Bmi_8bnvpxHZtb6EgHSHY-xn29W8VJMzjPU3fiCOv1bfjrNuA%40mail.gmail.com.
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Acquisition Timeout
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-------------------
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If all the available connections in the pool are busy, an HTTP request will wait until reaching a timeout. You can configure this timeout with :ref:`db-pool-acquisition-timeout`.
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If the request reaches the timeout, it will be aborted with the following response:
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.. code-block:: http
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HTTP/1.1 504 Gateway Timeout
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{"code":"PGRST003",
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"details":null,
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"hint":null,
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"message":"Timed out acquiring connection from connection pool."}
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Getting this error message is an indicator of a performance issue. To solve it, you can:
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- Reduce your queries execution time.
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- Check the request :ref:`explain_plan` to tune your query, this usually means adding indexes.
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- Reduce the amount of requests.
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- Reduce write requests. Do :ref:`bulk_insert` (or :ref:`upsert`) instead of inserting rows one by one.
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- Reduce read requests. Use :ref:`resource_embedding`. Combine unrelated data into a single request using custom database views or functions.
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- Use :ref:`s_procs` for combining read and write logic into a single request.
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- Increase the :ref:`pool growth limit <pool_growth_limit>`.
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- Not a panacea since connections can't grow infinitely. Try the previous recommendations before this.
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.. _automatic_recovery:
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Automatic Recovery
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------------------
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If the pool loses the connection to the database, it will retry reconnecting using exponential backoff. With 32 seconds being the maximum backoff time between retries.
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The retries happen immediately after a connection loss, if :ref:`db-channel-enabled` is set to true(the default). Otherwise they'll happen once a request arrives.
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To notify the client of the next retry, the server sends a ``503 Service Unavailable`` status with the ``Retry-After: x`` header. Where ``x`` is the number of seconds programmed for the next retry.
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.. _external_connection_poolers:
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Using External Connection Poolers
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---------------------------------
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It's possible to use external connection poolers, such as PgBouncer. Session pooling is compatible, while transaction pooling requires :ref:`db-prepared-statements` set to ``false``. Statement pooling is not compatible with PostgREST.
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Also set :ref:`db-channel-enabled` to ``false`` since ``LISTEN`` is not compatible with transaction pooling. Although it should not give any errors if left enabled.
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.. note::
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It’s not recommended to use an external connection pooler. `Our benchmarks <https://github.com/PostgREST/postgrest/issues/2294#issuecomment-1139148672>`_ indicate it provides much lower performance than PostgREST built-in pool.
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