c5668d99c9
Unlike with vnodes, each tablet is served only by a single shard, and it is associated with a memtable that, when flushed, it creates sstables which token-range is confined to the tablet owning them. On one hand, this allows for far better agility and elasticity since migration of tablets between nodes or shards does not require rewriting most if not all of the sstables, as required with vnodes (at the cleanup phase). Having too few tablets might limit performance due not being served by all shards or by imbalance between shards caused by quantization. The number of tabelts per table has to be a power of 2 with the current design, and when divided by the number of shards, some shards will serve N tablets, while others may serve N+1, and when N is small N+1/N may be significantly larger than 1. For example, with N=1, some shards will serve 2 tablet replicas and some will serve only 1, causing an imbalance of 100%. Now, simply allocating a lot more tablets for each table may theoretically address this problem, but practically: a. Each tablet has memory overhead and having too many tablets in the system with many tables and many tablets for each of them may overwhelm the system's and cause out-of-memory errors. b. Too-small tablets cause a proliferation of small sstables that are less efficient to acces, have higher metadata overhead (due to per-sstable overhead), and might exhaust the system's open file-descriptors limitations. The options introduced in this change can help the user tune the system in two ways: 1. Sizing the table to prevent unnecessary tablet splits and migrations. This can be done when the table is created, or later on, using ALTER TABLE. 2. Controlling min_per_shard_tablet_count to improve tablet balancing, for hot tables. Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
ScyllaDB Documentation
This repository contains the source files for ScyllaDB Open Source documentation.
- The
devfolder contains developer-oriented documentation related to the ScyllaDB code base. It is not published and is only available via GitHub. - All other folders and files contain user-oriented documentation related to ScyllaDB Open Source and are sources for opensource.docs.scylladb.com.
To report a documentation bug or suggest an improvement, open an issue in GitHub issues for this project.
To contribute to the documentation, open a GitHub pull request.
Key Guidelines for Contributors
- The user documentation is written in reStructuredText (RST) - a plaintext markup language similar to Markdown. If you're not familiar with RST, see ScyllaDB RST Examples.
- The developer documentation is written in Markdown. See Basic Markdown Syntax for reference.
- Follow the ScyllaDB Style Guide.
To prevent the build from failing:
-
If you add a new file, ensure it's added to an appropriate toctree, for example:
.. toctree:: :maxdepth: 2 :hidden: Page X </folder1/article1> Page Y </folder1/article2> Your New Page </folder1/your-new-article> -
Make sure the link syntax is correct. See the guidelines on creating links
-
Make sure the section headings are correct. See the guidelines on creating headings Note that the markup must be at least as long as the text in the heading. For example:
---------------------- Prerequisites ----------------------
Building User Documentation
Prerequisites
- Python
- poetry
- make
See the ScyllaDB Sphinx Theme prerequisites to check which versions of the above are currently required.
Mac OS X
You must have a working Homebrew in order to install the needed tools.
You also need the standard utility make.
Check if you have these two items with the following commands:
brew help
make -h
Linux Distributions
Building the user docs should work out of the box on most Linux distributions.
Windows
Use "Bash on Ubuntu on Windows" for the same tools and capabilities as on Linux distributions.
Building the Docs
- Run
make previewto build the documentation. - Preview the built documentation locally at http://127.0.0.1:5500/.
Cleanup
You can clean up all the build products and auto-installed Python stuff with:
make pristine
Information for Contributors
If you are interested in contributing to Scylla docs, please read the Scylla open source page at http://www.scylladb.com/opensource/ and complete a Scylla contributor agreement if needed. We can only accept documentation pull requests if we have a contributor agreement on file for you.
Third-party Documentation
-
Do any copying as a separate commit. Always commit an unmodified version first and then do any editing in a separate commit.
-
We already have a copy of the Apache license in our tree, so you do not need to commit a copy of the license.
-
Include the copyright header from the source file in the edited version. If you are copying an Apache Cassandra document with no copyright header, use:
This document includes material from Apache Cassandra.
Apache Cassandra is Copyright 2009-2014 The Apache Software Foundation.