Using Q4M - a message queue storage engine for MySQL

Using Q4M a message queue storage engine for MySQL Cybozu Labs, Inc. Kazuho Oku

Background 2 Apr 22 2009 Using Q4M

Who am I? Name: Kazuho Oku (奥一穂) Original Developer of Palmscape / Xiino The oldest web browser for Palm OS Working at Cybozu Labs since 2005 Research subsidiary of Cybozu, Inc. in Japan 3 Apr 22 2009 Using Q4M

About Cybozu, Inc. Japan’s largest groupware vendor Mostly provides as software products, not as services Some of our apps bundle MySQL as storage 4 Apr 22 2009 Using Q4M

About Pathtraq Started in Aug. 2007 Web ranking service One of Japan’s largest like Alexa, but semi-realtime, and per-page running on MySQL Need for a fast and reliable message relay for communication between the main server and content analysis server(s) 5 Apr 22 2009 Using Q4M

Design Goals of Q4M Robust Do not lose data on OS crash or power failure Fast Transfer thousands of messages per second Easy to Use Use SQL for access / maintenance Integration into MySQL no more separate daemons to take care of 6 Apr 22 2009 Using Q4M

What is a Message Queue? 7 Apr 22 2009 Using Q4M

What is a Message Queue? Middleware for persistent asynchronous communication communicate between fixed pairs (parties) a.k.a. Message Oriented Middleware MQ is intermediate storage RDBMS is persistent storage Senders / receivers may go down 8 Apr 22 2009 Using Q4M

Minimal Configuration of a MQ Senders and receivers access a single queue Sender Receiver Queue 9 Apr 22 2009 Using Q4M

MQ and Relays Separate queue for sender and receiver Messages relayed between queues Relay Sender Receiver Queue Queue 10 Apr 22 2009 Using Q4M

Merits of Message Relays Destination can be changed easily Relays may transfer messages to different locations depending on their headers Robustness against network failure no loss or duplicates when the relay fails Logging and Multicasting, etc. 11 Apr 22 2009 Using Q4M

Message Brokers Publish / subscribe model Separation between components and their integration Components read / write to predefined queues Integration is definition of routing rules between the message queues Messages are often transformed (filtered) within the relay agent 12 Apr 22 2009 Using Q4M

What about Q4M? Q4M itself is a message queue Can connect Q4M instances to create a message relay Provides API for creating message relays and brokers 13 Apr 22 2009 Using Q4M

Performance of Q4M over 7,000 mess/sec. message size: avg. 512 bytes syncing to disk Outperforming most needs if you need more, just scale out Can coexist with other storage engines without sacrificing their performance see http://labs.cybozu.co.jp/blog/kazuhoatwork/2008/06/q4m_06_release_and_benchmarks.php 14 Apr 22 2009 Using Q4M

Applications of Q4M 15 Apr 22 2009 Using Q4M

Asynchronous Updates Mixi (Japan's one of the largest SNS) uses Q4M to buffer writes to DB, to offload peak demands from http://alpha.mixi.co.jp/blog/?p=272 16 Apr 22 2009 Using Q4M

Connecting Distant Servers Pathtraq uses Q4M to create a relay between its database and content analysis processes → Contents to be analyzed → Content MySQL conn. Analysis Pathtraq over SSL,gzip Processes DB ← Results of the analysis ← 17 Apr 22 2009 Using Q4M

To Prefetch Data livedoor Reader (web-based feed aggregator) uses Q4M to prefetch data from database to memcached uses Q4M for scheduling web crawlers as well from http://d.hatena.ne.jp/mala/20081212/1229074359 18 Apr 22 2009 Using Q4M

Scheduling Web Crawlers Web crawlers with retry-on-error Sample code included in Q4M dist. If failed to fetch, store URL in retry queue Store Result Read URL Spiders URL DB Request Queue Retry Queue Re- scheduler 19 Apr 22 2009 Using Q4M

Delayed Content Generation Hatetter(RSS feed-to-twitter-API gateway) uses Q4M to delay content generation Source code: github.com/yappo/website-hatetter 20 Apr 22 2009 Using Q4M

User Notifications For sending notifications from web services DB App. Logic SMTP Agent Queue(s) IM Agent 21 Apr 22 2009 Using Q4M

Installing Q4M 22 Apr 22 2009 Using Q4M

Installing Q4M Compatible with MySQL 5.1 Download from q4m.31tools.com Binary releases available for some platforms Installing from source: requires source code of MySQL ./configure && make && make install run support-files/install.sql 23 Apr 22 2009 Using Q4M

Configuration Options of Q4M --with-sync=no|fsync|fdatasync|fcntl Controls synchronization to disk default: fdatasync on linux --enable-mmap Mmap’ed reads lead to higher throughput default: yes --with-delete=pwrite|msync msyncrecommended on linux>=2.6.20 if you need really high performance 24 Apr 22 2009 Using Q4M

Q4M Basics 25 Apr 22 2009 Using Q4M

The Model Various publishers write to queue Set of subscribers consume the entries in queue Publisher Q4M table Publisher Subscribers Publisher 26 Apr 22 2009 Using Q4M

Creating a Q4M Table  ENGINE=QUEUE creates mysql> CREATE TABLE qt ( -> id int(10) unsigned NOT NULL, a Q4M table -> message varchar(255) NOT NULL -> ) ENGINE=QUEUE; Query OK, 0 rows affected (0.42 sec)  No primary keys or indexes  Sorted by insertion order (it’s a queue) 27 Apr 22 2009 Using Q4M

Modifying Data on a Q4M Table  No restrictions for mysql> INSERT INTO qt (id,message) -> VALUES INSERT and DELETE -> (1,'Hello'), -> (2,'Bonjour'), -> (3,'Hola');  No support for UPDATE Query OK, 3 rows affected (0.02 sec) mysql> SELECT * FROM qt; +----+---------+ | id | message | +----+---------+ | 1 | Hello | | 2 | Bonjour | | 3 | Hola | +----+---------+ 3 rows in set (0.00 sec) 28 Apr 22 2009 Using Q4M

Calling queue_wait()  After calling, only one mysql> SELECT * FROM qt; +----+---------+ | id | message | row becomes visible +----+---------+ | 1 | Hello | from the connection | 2 | Bonjour | | 3 | Hola | +----+---------+ 3 rows in set (0.00 sec) mysql> SELECT queue_wait('qt'); +------------------+ | queue_wait('qt') | +------------------+ | 1| +------------------+ 1 row in set (0.00 sec) mysql> SELECT * FROM qt; +----+---------+ | id | message | +----+---------+ | 1 | Hello | +----+---------+ 1 row in set (0.00 sec) 30 Apr 22 2009 Using Q4M

OWNER Mode and NON-OWNER Mode In OWNER mode, only the OWNED row is visible OWNED row becomes invisible from other connections rows of other storage engines are visible NON-OWNER Mode OWNER Mode queue_wait() 1,'Hello' 1,'Hello' 2,'Bonjour' queue_end() 3,'Hola' queue_abort() 31 Apr 22 2009 Using Q4M

Consuming a Row  By calling mysql> SELECT queue_wait('qt'); (snip) mysql> SELECT * FROM qt; queue_end, the OWNED +----+---------+ | id | message | row is deleted, and +----+---------+ | 1 | Hello | connection returns to +----+---------+ 1 row in set (0.01 sec) NON-OWNER mode mysql> SELECT queue_end(); +-------------+ | queue_end() | +-------------+ | 1| +-------------+ 1 row in set (0.01 sec) mysql> SELECT * FROM qt; +----+---------+ | id | message | +----+---------+ | 2 | Bonjour | | 3 | Hola | +----+---------+ 2 rows in set (0.00 sec) 33 Apr 22 2009 Using Q4M

Writing a Subscriber  Call two functions: queue_wait, queue_end  Multiple subscribers can be run concurrently  each row in the queue is consumed only once while (true) { SELECT queue_wait('qt'); # switch to owner mode rows := SELECT * FROM qt; # obtain data if (count(rows) != 0) # if we have any data, then handle_row(rows[0]); # consume the row SELECT queue_end(); # erase the row from queue } 34 Apr 22 2009 Using Q4M

Writing a Subscriber (cont'd) Or call queue_wait as a condition Warning: conflicts with trigger-based insertions while (true) { rows := SELECT * FROM qt WHERE queue_wait('qt'); if (count(rows) != 0) handle_row(rows[0]); SELECT queue_end(); } 35 Apr 22 2009 Using Q4M

The Model – with code INSERT INTO queue ... Publisher while (true) { rows := SELECT * FROM qt WHERE queue_wait('qt'); if (count(rows) != 0) handle_row(rows[0]); INSERT INTO queue ... SELECT queue_end(); } Q4M table Publisher Subscribers INSERT INTO queue ... Publisher 36 Apr 22 2009 Using Q4M

Three Functions in Detail 37 Apr 22 2009 Using Q4M

queue_wait(table) Enters OWNER mode 0〜1 row becomes OWNED Enters OWNER mode even if no rows were available Default timeout: 60 seconds Returns 1 if a row is OWNED (0 on timeout) If called within OWNER mode, the owned row is deleted 38 Apr 22 2009 Using Q4M

Revisiting Subscriber Code Calls to queue_end just before queue_wait can be omitted while (true) { rows := SELECT * FROM qt WHERE queue_wait('qt'); if (count(rows) != 0) handle_row(rows[0]); SELECT queue_end(); } 39 Apr 22 2009 Using Q4M

Conditional queue_wait() Consume rows of certain condition Rows that do not match will be left untouched Only numeric columns can be checked Fast - condition tested once per each row examples: SELECT queue_wait('table:(col_a*3)+col_b<col_c'); SELECT queue_wait('table:retry_count<5'); 40 Apr 22 2009 Using Q4M

queue_wait(tbl_cond,[tbl_cond…,timeout]) Accepts multiple tables and timeout Data searched from leftmost table to right Returns table index (the leftmost table is 1) of the newly owned row Returns zero if no rows are being owned example: SELECT queue_wait('table_A','table_B',60); 41 Apr 22 2009 Using Q4M

Functions for Exiting OWNER Mode queue_end Deletes the owned row and exits OWNER mode queue_abort Releases (instead of deleting) the owned row and exits OWNER mode Close of a MySQL connection does the same thing 42 Apr 22 2009 Using Q4M

Relaying and Routing Messages 43 Apr 22 2009 Using Q4M

The Problem Relay (or router) consists of more than 3 processes, 2 conns No losses, no duplicates on crash or disconnection Q4M Table Q4M Table Relay Program (source) (dest.) 44 Apr 22 2009 Using Q4M

Internal Row ID Every row have a internal row ID invisible from Q4M table definition monotonically increasing 64-bit integer Used for detecting duplicates Use two functions to skip duplicates Data loss prevented by using queue_wait / queue_end 45 Apr 22 2009 Using Q4M

queue_rowid() Returns row ID of the OWNED row (if any) Returns NULL if no row is OWNED Call when retrieving data from source 46 Apr 22 2009 Using Q4M

queue_set_srcid(src_tbl_id, mode, src_row_id) Call before inserting a row to destination table Checks if the row is already inserted into the table, and ignores next INSERT if true Parameters: src_tbl_id - id to determine source table (0〜63) mode - quot;aquot; to drop duplicates, quot;wquot; to reset src_row_id - row ID obtained from source table 47 Apr 22 2009 Using Q4M

Pseudo Code Relays data from src_tbl to dest_tbl while (true) { # wait for data SELECT queue_wait(src_tbl) =>src_db; # read row and rowid row := (SELECT * FROM src_tbl =>src_db); rowid := (SELECT queue_rowid() =>src_db); # insert the row after setting srcid SELECT queue_set_srcid(src_tbl_id, 'a', rowid) =>dest_db; INSERT INTO dest_tbl (row) =>dest_db; 48 Apr 22 2009 Using Q4M

q4m-forward Simple forwarder script installed into mysql-dir/bin usage: q4m-forward [options] src_addrdest_addr example: % support-files/q4m-forward quot;dbi:mysql:database=db1;table=tbl1;user=foo;password=XXXquot; quot;dbi:mysql:database=db2;table=tbl2;host=bar;user=fooquot; options: --reset reset duplicate check info. --sender=idx slot no. used for checking duplicates (0..63, default: 0) --help 49 Apr 22 2009 Using Q4M

Limitations and the Future of Q4M 50 Apr 22 2009 Using Q4M

Things that Need to be Fixed Table compactions is a blocking operation runs when live data becomes <25% of log file very bad, though not as bad as it seems it's fast since it's a sequential write operation Relays are slow since transfer is done row-by-row Binlog does not work since MQ replication should be synchronous 51 Apr 22 2009 Using Q4M

Future of Q4M 2-phase commit with other storage engines (maybe) queue consumption and InnoDB updates can become atomic operation 52 Apr 22 2009 Using Q4M

Thank you http://q4m.31tools.com/ 53 Apr 22 2009 Using Q4M

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Using Q4M - a message queue storage engine for MySQL

by kazuho on Apr 22, 2009

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