Revision 2f41ecfe75f0ebf33e4969083b031c7a97ebaee7 authored by Zhongyi Xie on 23 August 2019, 20:54:09 UTC, committed by Facebook Github Bot on 23 August 2019, 20:55:34 UTC
Summary:
MyRocks currently sets `max_write_buffer_number_to_maintain` in order to maintain enough history for transaction conflict checking. The effectiveness of this approach depends on the size of memtables. When memtables are small, it may not keep enough history; when memtables are large, this may consume too much memory.
We are proposing a new way to configure memtable list history: by limiting the memory usage of immutable memtables. The new option is `max_write_buffer_size_to_maintain` and it will take precedence over the old `max_write_buffer_number_to_maintain` if they are both set to non-zero values. The new option accounts for the total memory usage of flushed immutable memtables and mutable memtable. When the total usage exceeds the limit, RocksDB may start dropping immutable memtables (which is also called trimming history), starting from the oldest one.
The semantics of the old option actually works both as an upper bound and lower bound. History trimming will start if number of immutable memtables exceeds the limit, but it will never go below (limit-1) due to history trimming.
In order the mimic the behavior with the new option, history trimming will stop if dropping the next immutable memtable causes the total memory usage go below the size limit. For example, assuming the size limit is set to 64MB, and there are 3 immutable memtables with sizes of 20, 30, 30. Although the total memory usage is 80MB > 64MB, dropping the oldest memtable will reduce the memory usage to 60MB < 64MB, so in this case no memtable will be dropped.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5022

Differential Revision: D14394062

Pulled By: miasantreble

fbshipit-source-id: 60457a509c6af89d0993f988c9b5c2aa9e45f5c5
1 parent 26293c8
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README.md
## User Documentation for rocksdb.org

This directory will contain the user and feature documentation for RocksDB. The documentation will be hosted on GitHub pages.

### Contributing

See [CONTRIBUTING.md](./CONTRIBUTING.md) for details on how to add or modify content.

### Run the Site Locally

The requirements for running a GitHub pages site locally is described in [GitHub help](https://help.github.com/articles/setting-up-your-github-pages-site-locally-with-jekyll/#requirements). The steps below summarize these steps.

> If you have run the site before, you can start with step 1 and then move on to step 5.

1. Ensure that you are in the `/docs` directory in your local RocksDB clone (i.e., the same directory where this `README.md` exists). The below RubyGems commands, etc. must be run from there.

1. Make sure you have Ruby and [RubyGems](https://rubygems.org/) installed.

   > Ruby >= 2.2 is required for the gems. On the latest versions of Mac OS X, Ruby 2.0 is the
   > default. Use `brew install ruby` (or your preferred upgrade mechanism) to install a newer
   > version of Ruby for your Mac OS X system.

1. Make sure you have [Bundler](http://bundler.io/) installed.

    ```
    # may require sudo
    gem install bundler
    ```
1. Install the project's dependencies

    ```
    # run this in the 'docs' directory
    bundle install
    ```

    > If you get an error when installing `nokogiri`, you may be running into the problem described
    > in [this nokogiri issue](https://github.com/sparklemotion/nokogiri/issues/1483). You can
    > either `brew uninstall xz` (and then `brew install xz` after the bundle is installed) or
    > `xcode-select --install` (although this may not work if you have already installed command
    > line tools).

1. Run Jekyll's server.

    - On first runs or for structural changes to the documentation (e.g., new sidebar menu item), do a full build.

    ```
    bundle exec jekyll serve
    ```

    - For content changes only, you can use `--incremental` for faster builds.

    ```
    bundle exec jekyll serve --incremental
    ```

    > We use `bundle exec` instead of running straight `jekyll` because `bundle exec` will always use the version of Jekyll from our `Gemfile`. Just running `jekyll` will use the system version and may not necessarily be compatible.

    - To run using an actual IP address, you can use `--host=0.0.0.0`

    ```
    bundle exec jekyll serve --host=0.0.0.0
    ```

    This will allow you to use the IP address associated with your machine in the URL. That way you could share it with other people.

    e.g., on a Mac, you can your IP address with something like `ifconfig | grep "inet " | grep -v 127.0.0.1`.    

1. Either of commands in the previous step will serve up the site on your local device at http://127.0.0.1:4000/ or http://localhost:4000.

### Updating the Bundle

The site depends on Github Pages and the installed bundle is based on the `github-pages` gem.
Occasionally that gem might get updated with new or changed functionality. If that is the case,
you can run:

```
bundle update
```

to get the latest packages for the installation.
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