personal presentation about scylladb 3.0 new feature

1. Scylladb 3.0 New
Chen Shi
2019/1/23

2. Agenda
• Hinted Handoff
• Allow Filtering support
• Streaming improvements
• Materialized Views
• Global Secondary Indexes
• Full, Multi-partition scan improvements
• New sstable format

3. Hinted Handoff
• 原因
• 很高的写负载
• 网络故障
• 硬件故障
• 好处
• 降低在节点故障期间造成的数据不一致的影响
• 降低repair工作量
• 降低read-repair时，checksum不一致的概率

4. Allow filtering
CREATE TABLE blogs (blogId int,
time1 int,
time2 int,
author text,
content text,
PRIMARY KEY(blogId, time1, time2));
SELECT * FROM blogs WHERE time1 = 1418306451235;
SELECT * FROM blogs WHERE author = ‘Jonathan Ellis’; Ok if author column is indexed
SELECT * FROM blogs WHERE author=’Jonathan Ellis’ and time2 = 1418306451235;
filtering is needed even author
and time2 column are indexed
DONOT always use allow filtering for your problem !
为了保持对cassandra和spark-Cassandra connector的兼容，以及对老数据集灵活查询的支持

5. Streaming
• 当有新节点加入(bootstrap)、退出(decommission)、repair时，节点
对应的数据从一方流向另一方
• 老版本中，接收方需要先将数据放到memtable，满了后，再flush到
sstable；新版本绕过memtable直接写sstable
• 好处
• 降低内存开销（可用于服务于请求）
• 不用再对迁移过来的数据的memtable插入、排序，降低CPU cycles
• 更少的sstable compactions

6. Materialized Views
• 一个存储某种查询的结果的表 (base table -> view table, denormalization)
• 不能直接对其更新，但更新base table会异步更新它
• 二级索引建立在其上
Scylla Summit 2017- Distributed Materialized Views

7. Global Secondary Indexes
• Cassandra 二级索引 (local indexes)
• 数据在哪，索引就在哪
• 写很快，但读可能要查询其它节点；且不具备扩展性
• Scylla global indexing
CREATE TABLE ks.users (
userid uuid,
name text,
email text,
country text,
PRIMARY KEY (userid)
);
CREATE INDEX ON ks.users (email); CREATE MATERIALIZED VIEW
ks.users_email_idx_index AS
SELECT email, userid
FROM ks.users
WHERE email IS NOT NULL
PRIMARY KEY (email, userid)
WITH CLUSTERING ORDER BY
(userid ASC);
选用二级索引还是MV取决于应用

8. Full, Multi-partition scan improvements
• 一种控制算法，提高range query性能
• 算法本身使用了缓冲和预读，以防止读被中止
• 好处
• 提高了系统响应
• 减少了disk read，range scan性能提高

9. New sstable format
• 兼容Cassandra 3.x sstables
• 比Scylla 老版本快

10. Reference
• Scylla blog: 3.0 Overview
• 3.0 Release Notes
• Scylla doc: Hinted handoff
• Cassandra blog: Allow filtering
• Scylla blog: secondary index & Cassandra blog: native secondary index