如何理解dqlite

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dqlite是一個 C library，實現了一個嵌入式的可復制SQL database engine，具有高可用和自動失效恢復的特性。

名稱 "dqlite" 意味著 "distributed SQLite"，是 dqlite 擴展了 SQLite 而來。SQLite主要單機使用，而dqlite添加了 network protocol可以將多個應用實例鏈接為一個高可用的集群，而且不需要依賴其他的外部數據庫。

使用dqlite的Kubernetes分發版包括MicroK8s和K3s。

主要特性

能力：

• 完全同步的 network 和 disk I/O

• Comprehensive test suite for correctness

• Benchmarked for memory footprint and network efficiency

• 持久化存儲用于transaction logs

• 快速恢復，用于system restore

• 穩定的 Golang 客戶端，文檔包含 wire protocol 用于其它語言的實現。

• 支持 ARM, X86, POWER 和 IBM Z architectures

特性：

• 超低時延，C-Raft 最小化交易延遲。

• 移植性，C-Raft 和 dqlite 都用c語言編寫，提供多平臺支持。

• 開源，采用Apache 2.0 許可，最大的兼容性。

• 可用，Includes common CLI pattern for database initialization and voting member joins and departures.

• 快速失效回復，Minimal, tunable delay for failover with automatic leader election.

• 持續性，Disk-backed database with in-memory options and SQLite transactions.

• 設計特性，Asynchronous single-threaded implementation using libuv as event loop.

• 自定義的wire protocol，優化了SQLite primitives 和 data types.

• 數據復制，基于 Raft algorithm 和高效的 C-raft 實現。

許可

The dqlite library is released under a slightly modified version of LGPLv3, that includes a copyright exception letting users to statically link the library code in their project and release the final work under their own terms. See the full license text.

試用

The simplest way to see dqlite in action is to use the demo program that comes with the Go dqlite bindings. Please see the relevant documentation in that project.

媒體

A talk about dqlite was given at FOSDEM 2020, you can watch it here.

協議-Wire protocol

If you wish to write a client, please refer to the wire protocol documentation.

快速安裝

If you are on a Debian-based system, you can the latest stable release from dqlite's stable PPA:

sudo add-apt-repository ppa:dqlite/stable
sudo apt-get update
sudo apt-get install libdqlite-dev

源碼構建

To build libdqlite from source you'll need:

• A reasonably recent version of libuv (v1.8.0 or beyond).

• A patched version of SQLite with support for WAL-based replication.

• A build of the C-raft Raft library.

• A build of the libco coroutine library.

Your distribution should already provide you a pre-built libuv shared library.

To build the other libraries:

git clone --depth 100 https://github.com/canonical/sqlite.git
cd sqlite
./configure --enable-replication
make
sudo make install
cd ..
git clone https://github.com/canonical/libco.git
cd libco
make
sudo make install
cd ..
git clone https://github.com/canonical/raft.git
cd raft
autoreconf -i
./configure
make
sudo make install
cd ..

Once all required libraries are installed, to in order to build the dqlite shared library itself you can run:

autoreconf -i
./configure
make
sudo make install

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