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Update documentation about how to upgrade Jemalloc.

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antirez 2018-05-24 17:16:12 +02:00
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deps/README.md vendored
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@ -13,13 +13,30 @@ How to upgrade the above dependencies
Jemalloc
---
Jemalloc is unmodified. We only change settings via the `configure` script of Jemalloc using the `--with-lg-quantum` option, setting it to the value of 3 instead of 4. This provides us with more size classes that better suit the Redis data structures, in order to gain memory efficiency.
So in order to upgrade jemalloc:
Jemalloc is modified with changes that allow us to implement the Redis
active defragmentation logic. However this feature of Redis is not mandatory
and Redis is able to understand if the Jemalloc version it is compiled
against supports such Redis-specific modifications. So in theory, if you
are not interested in the active defragmentation, you can replace Jemalloc
just following tose steps:
1. Remove the jemalloc directory.
2. Substitute it with the new jemalloc source tree.
However note that we change Jemalloc settings via the `configure` script of Jemalloc using the `--with-lg-quantum` option, setting it to the value of 3 instead of 4. This provides us with more size classes that better suit the Redis data structures, in order to gain memory efficiency.
Instead if you want to upgrade Jemalloc while also providing support for
defragmentation, you have to replace it with a newer version, and make
the following changes:
1. In Jemalloc three, file `include/jemalloc/jemalloc_macros.h.in`, make sure
to add `#define JEMALLOC_FRAG_HINT`.
2. Implement the function `je_get_defrag_hint()` inside `src/jemalloc.c`. You
can see how it is implemented in the current Jemalloc source tree shipped
with Redis, and rewrite it according to the new Jemalloc internals, if they
changed, otherwise you could just copy the old implementation if you are
upgrading just to a similar version of Jemalloc.
Geohash
---