02 Aggregation Improvements in MySQL Outline 01 Aggregation Report in MySQL 03 Row vs Column Oriented Databases 04 Integration with ClickHouse 05 Deduplication in ClickHouse 07 Q&A 06 Optimizations in ClickHouse
Report is Everywhere Daily revenue for product orders Analysis for top-selling products Ranks for most-clicked articles or videos Total cost for business operation Statements for financial department Summaries of registered users Statistics of unique visitors ... etc.
Data Source database, files, services Condition Filters resource id, time range, numbers, text, data type Aggregations sum, average, count, max, min Transformers concat, mask, numbers format Groups Orders Basic Elements of Report
How much time does it take for this query if your data
rows is 1000, 10k, 1m, 10m or 100m? Report Performance in MySQL SELECT product_id, COUNT(id) as count WHERE status != 'canceled' GROUP BY product_id ORDER BY count DESC LIMIT 10 id user_id product_id amount discount shipping_fee total status created_at 1 35 2 1000 50 0 950 shipped 2022-11-11 09:24:13 2 78 5 860 20 60 900 paid 2022-11-11 10:12:04 3 93 11 780 0 60 840 canceled 2022-11-12 01:39:17
Add Appropriate Indexes Only helps filtering rows, not aggregation Too many indexes is not a good idea Partitions and Shardings Suitable for unchanged conditions combination Complicated and limited usage (join, transactions... etc) Vertical Scaling Database There's hard limit for single server Money is always not a problem Aggregation Improvements in MySQL
Text Select Select Select Date Date Date Search Select Date Filters for Users' Needs Aggregation Improvements in MySQL Name: Gender: City: Status: Shipping Date: Order Date: Accounting Date: Agent: Updated Date:
There's not much you can do with MySQL if... Data rows are large for aggregation (over 10 million) Filtering conditions are flexible Data rows are mutable Near real-time requirement Aggregation Improvements in MySQL
Row Oriented Databases Data associated with the same record are kept next to each
other in memory Optimized for reading and writing a single row of data Common in OLTP database like MySQL, Postgres etc. Row vs Column Oriented Databases id name country age 1 Taylor USA 35 2 Evan China 35
Pros of Columnar Database Queries that use only a few columns out of many Aggregating queries against large volumes of data Column-wise data compression Cons of Columnar Database Poor at data mutations like update or delete Not optimized for querying row-specific data Lack of unique constraints Row vs Column Oriented Databases
An open source (Apache 2.0), relational, OLAP database since 2016 Was originally developed as an internal project by Yandex (a Russian search engine) The word ClickHouse is a combination of Clickstream and Data WareHouse Known for extremely high query speed and performance Fully based on ANSI SQL, which makes it easier to interact with Highly productive development on Github Many companies are using ClickHouse in production like Uber, Slack, Tesla, Tencent, Tiktok, Cloudflare, etc. Introduction of ClickHouse
Data Syncing Flow Integration with ClickHouse id name age updated_at 1 Taylor 35 2022-12-01 00:00:00 2 Evan 35 2022-12-01 00:00:00 id name age updated_at 1 Taylor 35 2022-12-01 00:00:00 2 Evan 35 2022-12-01 00:00:00
Data Syncing Flow Integration with ClickHouse id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 insert id name age updated_at 1 Taylor 35 2022-12-01 00:00:00 2 Evan 35 2022-12-01 00:00:00
Data Syncing Flow Integration with ClickHouse id name age updated_at 1 Taylor 35 2022-12-01 00:00:00 2 Evan 35 2022-12-01 00:00:00 1 Taylor 36 2022-12-01 00:01:00 id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 ?
Data Syncing Flow Integration with ClickHouse id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 Deduplicate
UPDATE/DELETE mutations ReplacingMergeTree / CollapsingMergeTree with FINAL modifier with OPTIMIZE statement Aggregate Function MaterializedMySQL Database Engine Altinity Sink Connector Lightweight DELETE feature UniqueMergeTree in ByteHouse (not implemented) Deduplication in ClickHouse
UPDATE/DELETE mutations UPDATE and DELETE are not supported in early versions Mutations are extremely heavy operations Mutations are asynchronous by default There's no transaction guaranteed Deduplication in ClickHouse ALTER TABLE authors DELETE WHERE id = 1 INSERT INTO authors VALUEs (1, 'Taylor', 36, '2022-12-01 00:00:00')
ReplacingMergeTree / CollapsingMergeTree ReplacingMergeTree will deduplicate data by itself Merge timing is controlled by ClickHouse Need to use FINAL or OPTIMIZE to force merging Deduplication in ClickHouse id name age updated_at 1 Taylor 35 2022-12-01 00:00:00 2 Evan 35 2022-12-01 00:00:00 1 Taylor 36 2022-12-01 00:01:00 id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 Deduplicate
ReplacingMergeTree / CollapsingMergeTree with FINAL modifier FINAL will slow down the query performance FINAL runs on single thread, and improved as multi-thread in
lately versions Deduplication in ClickHouse SELECT * FROM authors FINAL
OPTIMIZE TABLE authors PARTITION '202212' FINAL ReplacingMergeTree / CollapsingMergeTree with OPTIMIZE statement OPTIMIZE will trigger partitions merge immediately OPTIMIZE will use lots of CPU and disk resource Needs to enable optimize_throw_if_noop for exception Can be optimized with specific partitions Deduplication in ClickHouse 202211 ... unchanged 202212 merge duplicated
Aggregate Function argMax with GROUP BY Create a view for better query experience Duplicated data still exists, but being filtered Difficult for performance optimization in some complicated
queries Deduplication in ClickHouse CREATE VIEW authors_view AS SELECT id, argMax(name, updated_at) as name, argMax(age, updated_at) as age, max(updated_at) as updated_at FEOM authors GROUP BY id
MaterializedMySQL('localhost:3306', 'db', 'user', '***') SETTINGS allows_query_when_mysql_lost=true, max_wait_time_when_mysql_unavailable=10000; MaterializedMySQL Database Engine Experimental feature, not production ready Some data types are not supported Implicit errors will stop all replication process Deduplication in ClickHouse
Altinity Sink Connector Still in early stage of development Support INSERT, UPDATE and DELETE Rely on row policy and FINAL modifier Deduplication in ClickHouse (https://altinity.com/blog/using-clickhouse-as-an-analytic-extension-for-mysql)
Lightweight DELETE Feature Experiment feature in ClickHouse 22.8 Lightweight deletes are asynchronous by default Still don't use it as aggressively as on an OLTP system Implement with bitmap mechanism, deleted data are filtered There's no transaction guaranteed between delete and insert Deduplication in ClickHouse DELETE FROM authors WHERE id = 1 INSERT INTO authors VALUEs (1, 'Taylor', 36, '2022-12-01 00:00:00')
Adopted Solutions ReplacingMergeTree with FINAL INSERT and OPTIMIZE tables Lightweight DELETE (current version) How about transaction guarantee? Deduplication in ClickHouse DELETE FROM authors WHERE id = 1 INSERT INTO authors VALUEs (1, 'Taylor', 36, '2022-12-01 00:00:00')
Deduplication in ClickHouse id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 id name age updated_at 1 Taylor 36 2022-12-01 00:01:00 2 Evan 35 2022-12-01 00:00:00 Original Table Replica Table sync Alternative for FINAL Modifier To prevent duplicated data during the merge To make it more performant than FINAL Sync to replica table first, then redirect queries to replica
Deduplication in ClickHouse UniqueMergeTree in ByteHouse Implement mutations with mark-delete and insert Similar concepts to lightweight delete + insert, but based on
a table engine level There's an RFC, but not being accepted yet:
Integration with Laravel ClickHouse Packages smi2/phpclickhouse the-tinderbox/clickhouse-builder (support eloquent builder) bavix/laravel-clickhouse (support eloquent model) Only basic grammar support for ClickHouse features
Optimizations in ClickHouse Partitions (https://www.slideshare.net/Altinity/webinar-secrets-of-clickhouse-query-performance-by-robert-hodges-173379008)
SELECT orders.user_id, sum(orders.revenue) FROM orders LEFT JOIN users on orders.user_id = users.id WHERE users.rank = 'gold' group by orders.user_id order by orders.user_id limit 10 SELECT orders.user_id, sum(orders.revenue) FROM orders WHERE orders.user_id IN (SELECT id FROM users
WHERE rank = 'gold') group by orders.user_id order by orders.user_id limit 10 Optimizations in ClickHouse Use SubQuery Rather Than JOIN
Optimizations in ClickHouse Use Small Table as Right Table in JOIN ClickHouse reads all data from right table first as hash map (https://zhuanlan.zhihu.com/p/377506070)
Optimizations in ClickHouse Filter before Aggregation SELECT COUNT(), SUM(revenue), platform_id FROM orders GROUP BY platform_id HAVING finished_at > '2022-01-01' SELECT COUNT(), SUM(revenue), platform_id FROM orders WHERE finished_at > '2022-01-01' GROUP BY platform_id
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