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[Cache] Expand the docs about the cache chain #12770

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Dec 7, 2019
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[Cache] Expand the docs about the cache chain #12770

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20 changes: 15 additions & 5 deletions cache.rst
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Expand Up @@ -397,11 +397,21 @@ and use that when configuring the pool.
Creating a Cache Chain
----------------------

Different cache adapters have different strengths and weaknesses. Some might be really
quick but small and some may be able to contain a lot of data but are quite slow.
To get the best of both worlds you may use a chain of adapters. The idea is to
first look at the quick adapter and then move on to slower adapters. In the worst
case the value needs to be recalculated.
Different cache adapters have different strengths and weaknesses. Some might be
really quick but optimized to store small items and some may be able to contain
a lot of data but are quite slow. To get the best of both worlds you may use a
chain of adapters.

A cache chain combines several cache pools into a single one. When storing an
item in a cache chain, Symfony stores it in all pools sequentially. When
retrieving an item, Symfony tries to get it from the first pool. If it's not
found, it tries the next pools until the item is found or an exception is thrown.
Because of this behavior, it's recommended to define the adapters in the chain
in order from the fastest to the slowest.

If an error happens when storing an item in a pool, Symfony stores it in the
other pools and no exception is thrown. Later, when the item is retrieved,
Symfony stores the item automatically in all the missing pools.

.. configuration-block::

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