f8aaeb5e87
ScyllaDB has special counter columns for which atomic add/subtract
operations like `SET a = a + 1` are allowed. Such operations have not
been allowed on ordinary non-counter columns, as they would not be
properly atomic - the read an the write are separate, and concurrent
operations can have incorrect results.
This patch makes it allowed to use such atomic add/subtract operations
in *LWT* statements. Some examples:
UPDATE ... SET a = a - 1 IF a > 0
UPDATE ... SET a = a + 1 IF EXISTS
UPDATE ... SET a = a + 1 a != NULL
The row updated in the operation, and the updated column (a) should
be initialized before the update - arithmetic operations on missing
column values silently leave the column null (no error is generated).
This add/subtract operations is allowed on any numeric column -
integer or floating point of any size.
The ability of LWT to fetch the old values of a column and use it to
calculate the new value has long been available in our internal CAS
implementation - and has been in use for years in Alternator - but until
this patch it was not exposed in CQL's LWT.
This patch does not add new syntax to CQL - the "SET a = a + b"
and "SET a = a - b" syntax that already existed for counters is now
allowed for non-counters.
This is a new Scylla-only feature that does not exist in Cassandra.
Fixes #10568
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
ScyllaDB Documentation
This repository contains the source files for ScyllaDB 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 and are sources for docs.scylladb.com/manual.
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 previewin thedocs/directory to 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.