9de52b1c98
We are planning to improve some usages of compression in Scylla (in which we compress small blocks of data) by pre-training compression dictionaries on similar data seen so far. For example, many RPC messages have similar structure (and likely similar data), so the similarity could be exploited for better compression. This can be achieved e.g. by training a dictionary on the RPC traffic, and compressing subsequent RPC messages against that dictionary. To work well, the training should be fed a representative sample of the compressible data. Such a sample can be approached by taking a random subset (of some given reasonable size) of the data, with uniform probability. For our purposes, we need an online algorithm for this -- one which can select the random k-subset from a stream of arbitrary size (e.g. all RPC traffic over an hour), while requiring only the necessary minimum of memory. This is a known problem, called "reservoir sampling". This PR introduces `reservoir_sampler`, which implements an optimal algorithm for reservoir sampling. Additionally, it introduces `page_sampler` -- a wrapper for `reservoir_sampler`, which uses it to select a random sample of pages from a stream of bytes.
Scylla in-source tests.
For details on how to run the tests, see docs/dev/testing.md
Shared C++ utils, libraries are in lib/, for Python - pylib/
alternator - Python tests which connect to a single server and use the DynamoDB API unit, boost, raft - unit tests in C++ cqlpy - Python tests which connect to a single server and use CQL topology* - tests that set up clusters and add/remove nodes cql - approval tests that use CQL and pre-recorded output rest_api - tests for Scylla REST API Port 9000 scylla-gdb - tests for scylla-gdb.py helper script nodetool - tests for C++ implementation of nodetool
If you can use an existing folder, consider adding your test to it. New folders should be used for new large categories/subsystems, or when the test environment is significantly different from some existing suite, e.g. you plan to start scylladb with different configuration, and you intend to add many tests and would like them to reuse an existing Scylla cluster (clusters can be reused for tests within the same folder).
To add a new folder, create a new directory, and then
copy & edit its suite.ini.