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When investigating OOM:s a prominent pattern is a size class that is exploded, using up most of the available memory alone. If one is lucky, the objects causing the OOM are instances of some virtual class, making their identification easy. Other times the objects are referenced by instances of some virtual class, allowing their identification with some work. However there are cases where neither these objects nor their direct referrers are instances of virtual classes. This is the case `scylla generate_object_graph` intends to help. scylla generate_object_graph, like its name suggests generates the object graph of the requested object. The object graph is a directed graph, where vertices are objects and edges are references between them, going from referrers to the referee. The vertices contain information, like the address of the object, its size, whether it is a live or not and if applies, the address and symbol name of its vtable. The edges contain the list of offsets the referrer has references at. The generated graph is an image, which allows the visual inspection of the object graph, allowing the developer to notice patterns and hopefully identify the problematic objects. The graph is generated with the help of `graphwiz`. The command generates `.dot` files which can be converted to images with the help of the `dot` utility. The command can do this if the output file is one of the supported image formats (e.g. `png`), otherwise only the `.dot` file is generated, leaving the actual image generation to the user.
Scylla
Quick-start
To get the build going quickly, Scylla offers a frozen toolchain which would build and run Scylla using a pre-configured Docker image. Using the frozen toolchain will also isolate all of the installed dependencies in a Docker container. Assuming you have met the toolchain prerequisites, which is running Docker in user mode, building and running is as easy as:
$ ./tools/toolchain/dbuild ./configure.py
$ ./tools/toolchain/dbuild ninja build/release/scylla
$ ./tools/toolchain/dbuild ./build/release/scylla --developer-mode 1
Please see HACKING.md for detailed information on building and developing Scylla.
Note: GCC >= 8.1.1 is required to compile Scylla.
Running Scylla
- Run Scylla
./build/release/scylla
- run Scylla with one CPU and ./tmp as data directory
./build/release/scylla --datadir tmp --commitlog-directory tmp --smp 1
- For more run options:
./build/release/scylla --help
Scylla APIs and compatibility
By default, Scylla is compatible with Apache Cassandra and its APIs - CQL and Thrift. There is also experimental support for the API of Amazon DynamoDB, but being experimental it needs to be explicitly enabled to be used. For more information on how to enable the experimental DynamoDB compatibility in Scylla, and the current limitations of this feature, see Alternator and Getting started with Alternator.
Building Fedora RPM
As a pre-requisite, you need to install Mock on your machine:
# Install mock:
sudo yum install mock
# Add user to the "mock" group:
usermod -a -G mock $USER && newgrp mock
Then, to build an RPM, run:
./dist/redhat/build_rpm.sh
The built RPM is stored in /var/lib/mock/<configuration>/result directory.
For example, on Fedora 21 mock reports the following:
INFO: Done(scylla-server-0.00-1.fc21.src.rpm) Config(default) 20 minutes 7 seconds
INFO: Results and/or logs in: /var/lib/mock/fedora-21-x86_64/result
Building Fedora-based Docker image
Build a Docker image with:
cd dist/docker
docker build -t <image-name> .
Run the image with:
docker run -p $(hostname -i):9042:9042 -i -t <image name>