1fefe597e6
When wiring multi range reader with cleanup, I found that cleanup
wouldn't be able to release disk space of input SSTables earlier.
The reason is that multi range reader fast forward to the next range,
therefore it enables mutation_reader::forwarding, and as a result,
combined reader cannot release readers proactively as it cannot tell
for sure that the underlying reader is exhausted. It may have reached
EOS for the current range, but it may have data for the next one.
The concept of EOS actually only applies to the current range being
read. A reader that returned EOS will actually get out of this
state once the combined reader fast forward to the next range.
Therefore, only the underlying reader, i.e. the sstable reader,
can for certain know that the data source is completely exhausted,
given that tokens are read in monotonically increasing order.
For reversed reads, that's not true but fast forward to range
is not actually supported yet for it.
Today, the SSTable reader already knows that the underlying SSTable
was exhausted in fast_forward_to(), after it call index_reader's
advance_to(partition_range), therefore it disables subsequent
reads. We can take a step further and also check that the index
was exhausted, i.e. reached EOF.
So if the index is exhausted, and there's no partition to read
after the fast_forward_to() call, we know that there's nothing
left to do in this reader, and therefore the reader can be
closed proactively, allowing the disk space of SSTable to be
reclaimed if it was already deleted.
We can see that the combined reader, under multi range reader,
will incrementally find a set of disjoint SSTable exhausted,
as it fast foward to owned ranges
1:
INFO 2023-07-05 10:51:09,570 [shard 0] mutation_reader - flat_multi_range_mutation_reader(): fast forwarding to range [{-4525396453480898112, start},{-4525396453480898112, end}]
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-1-big-Data.db, start == *end, eof ? true
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - closing reader 0x60100029d800 for /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-1-big-Data.db
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-3-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-4-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-5-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-6-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-7-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-8-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-9-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,570 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-10-big-Data.db, start == *end, eof ? false
2:
INFO 2023-07-05 10:51:09,572 [shard 0] mutation_reader - flat_multi_range_mutation_reader(): fast forwarding to range [{-2253424581619911583, start},{-2253424581619911583, end}]
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-2-big-Data.db, start == *end, eof ? true
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - closing reader 0x60100029d400 for /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-2-big-Data.db
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-4-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-5-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-6-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-7-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-8-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-9-big-Data.db, start == *end, eof ? false
INFO 2023-07-05 10:51:09,572 [shard 0] sstable - sstable /tmp/scylla-9831a31a-66f3-4541-8681-000ac8e21bbb/me-10-big-Data.db, start == *end, eof ? false
And so on.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Scylla
What is Scylla?
Scylla is the real-time big data database that is API-compatible with Apache Cassandra and Amazon DynamoDB. Scylla embraces a shared-nothing approach that increases throughput and storage capacity to realize order-of-magnitude performance improvements and reduce hardware costs.
For more information, please see the ScyllaDB web site.
Build Prerequisites
Scylla is fairly fussy about its build environment, requiring very recent versions of the C++20 compiler and of many libraries to build. The document HACKING.md includes detailed information on building and developing Scylla, but to get Scylla building quickly on (almost) any build machine, Scylla offers a frozen toolchain, This is a pre-configured Docker image which includes recent versions of all the required compilers, libraries and build tools. Using the frozen toolchain allows you to avoid changing anything in your build machine to meet Scylla's requirements - you just need to meet the frozen toolchain's prerequisites (mostly, Docker or Podman being available).
Building Scylla
Building Scylla with the frozen toolchain dbuild is as easy as:
$ git submodule update --init --force --recursive
$ ./tools/toolchain/dbuild ./configure.py
$ ./tools/toolchain/dbuild ninja build/release/scylla
For further information, please see:
- Developer documentation for more information on building Scylla.
- Build documentation on how to build Scylla binaries, tests, and packages.
- Docker image build documentation for information on how to build Docker images.
Running Scylla
To start Scylla server, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --workdir tmp --smp 1 --developer-mode 1
This will start a Scylla node with one CPU core allocated to it and data files stored in the tmp directory.
The --developer-mode is needed to disable the various checks Scylla performs at startup to ensure the machine is configured for maximum performance (not relevant on development workstations).
Please note that you need to run Scylla with dbuild if you built it with the frozen toolchain.
For more run options, run:
$ ./tools/toolchain/dbuild ./build/release/scylla --help
Testing
See test.py manual.
Scylla APIs and compatibility
By default, Scylla is compatible with Apache Cassandra and its APIs - CQL and Thrift. There is also support for the API of Amazon DynamoDB™, which needs to be enabled and configured in order to be used. For more information on how to enable the DynamoDB™ API in Scylla, and the current compatibility of this feature as well as Scylla-specific extensions, see Alternator and Getting started with Alternator.
Documentation
Documentation can be found here. Seastar documentation can be found here. User documentation can be found here.
Training
Training material and online courses can be found at Scylla University. The courses are free, self-paced and include hands-on examples. They cover a variety of topics including Scylla data modeling, administration, architecture, basic NoSQL concepts, using drivers for application development, Scylla setup, failover, compactions, multi-datacenters and how Scylla integrates with third-party applications.
Contributing to Scylla
If you want to report a bug or submit a pull request or a patch, please read the contribution guidelines.
If you are a developer working on Scylla, please read the developer guidelines.
Contact
- The community forum and Slack channel are for users to discuss configuration, management, and operations of the ScyllaDB open source.
- The developers mailing list is for developers and people interested in following the development of ScyllaDB to discuss technical topics.