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5b88d6b4d6
Currently querier_cache uses a `std::unordered_map<utils::UUID, querier>`
to store cache entries and an `std::list<meta_entry>` to store meta
information about the querier entries, like insertion order, expiry
time, etc.
All cache eviction algorithms use the meta-entry list to evict entries
in reverse insertion order (LRU order). To make this possible
meta-entries keep an iterator into the entry map so that given a
meta-entry one can easily erase the querier entry. This however poses a
problem as std::unordered_map can possibly invalidate all its iterators
when new items are inserted. This is use-after-free waiting to happen.
Another disadvantages of the current solution is that it requires the
meta-entry to use a weak pointer to the querier entry so that in case
that is removed (as a result of a successful lookup) it doesn't try to
access it. This has an impact on all cache eviction algorithms as they
have to be prepared to deal with stale meta-entries. Stale meta-entries
also unnecesarily consume memory.
To solve these problems redesign how querier_cache stores entries
completely. Instead of storing the entries in an `std::unordered_map`
and storing the meta-entries in an `std::list`, store the entries in an
`std::list` and an intrusive-map (index) for lookups. This new design
has severeal advantages over the old one:
* The entries will now be in insert order, so eviction strategies can
work on the entry list itself, no need to involve additional data
structures for this.
* All data related to an entry is stored in one place, no data
duplication.
* Removing an entry automatically removes it from the index as intrusive
containers support auto unlink. This means there is no need to store
iterators for long terms, risking use-after-free when the container
invalidates it's iterators.
Additional changes:
* Modify eviction strategies so that they work with the `entry`
interface rather than the stored value directly.
Ref #3424
(cherry picked from commit 7ce7f3f0cc)
Scylla
Quick-start
$ git submodule update --init --recursive
$ sudo ./install-dependencies.sh
$ ./configure.py --mode=release
$ ninja-build -j4 # Assuming 4 system threads.
$ ./build/release/scylla
$ # Rejoice!
Please see HACKING.md for detailed information on building and developing 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
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>