17 Things Developers should know about Databases...High Availability Design Choices You want instant...
Transcript of 17 Things Developers should know about Databases...High Availability Design Choices You want instant...
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© 2019 Percona. 1
Peter Zaitsev
17 Things Developers should know about Databases
CEO, PerconaRyazan, Russia
November 5th, 2019
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Who Are you ?
More Developer ?
More OPS ?
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Ops
Focused on Database Only
Generalist
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Programming Language
•What Programming Languages does your team use ?
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Devs vs Ops
DevOps suppose to have solved it but tension is still common between Devs and Ops
Especially with Databases which are often special snowflake
Especially with larger organizations
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Large Organizations
•Ops vs Ops have conflict too
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Devs vs Ops Conflict
•Devs•Why is this stupid database always the problem. •Why can’t it just work and work fast
•Ops•Why do not learn schema design•Why do not you write optimized queries•Why do not you think about capacity planning
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Database Responsibility
•Shared Responsibility for Ultimate Success
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Top Recommendations for Developers
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Learn Database Basics
You can’t build great database powered applications if you do not understand how databases work
Schema Design
Power of the Database Language
How Database Executes the Query
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Query Execution Diagram
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EXPLAIN
https://dev.mysql.com/doc/refman/8.0/en/execution-plan-information.html
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Which Queries are Causing the Load
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Why Are they Causing this Load
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How to Improve their Performance
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Check out PMM
http://pmmdemo.percona.com
PMM v 2 is now GA
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How are Queries Executed ?
Single Threaded
Single Node
Distributed
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Indexes
Indexes are Must Indexes are Expensive
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Capacity Planning
No Database can handle “unlimited scale”
Scalability is very application dependent
Trust Measurements more than Promises
Can be done or can be done Efficiently ?
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Vertical and Horizontal Scaling
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Scalable != Efficient
The Systems which promote a scalable can be less efficient
Hadoop, Cassandra, TiDB are great examples
By only the wrong thing you can get in trouble
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TiDB Scalability (Single Node)
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TiDB Efficiency
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Throughput != Latency
•If I tell you system can do 100.000 queries/sec would you say it is fast ?
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Speed of Light Limitations
High Availability Design Choices
You want instant durable replication over wide geography or Performance ?
Understanding Difference between High Availability and Disaster Recovery protocols
Network Bandwidth is not the same as Latency
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Also Understand
Connections to the database are expensive
Especially if doing TLS Handshake
Query Latency Tends to Add Up
Especially on real network and not your laptop
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ORM (Object-Relational-Mapping)
Allows Developers to query the database without need to understand SQL
Can create SQL which is very inefficient
Learn SQL Generation “Hints”, Learn JPQL/HQL advanced features
Be ready to manually write SQL if there is no other choice
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Do not Leave Transactions Open
Open Connection is rather inexpensive
Transaction open for Long Time can get very expensive (even if it performed no writes)
Isolation Mode Matters
SET AUTOCOMMIT=0 - Any SELECT query will Open Transaction
COMMIT/ROLLBACK closes transaction
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Understanding Optimal Concurrency
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Queueing
Request Queueing is Normal
With requests coming at “Random Arrivals” some queueing will happen with any system scale
Should not happen to often or for very long
Queueing is “Cheaper” Close to the User
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Benefits of Connection Pooling
Avoiding Connection Overhead,
especially TLS/SSL
Avoiding using Excessive Number
of Database Connections
Multiplexing/Load Management
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Configuring Connection Pool
Default and Maximum Connection Pool Size
Scaling Parameters
Combined Connection Pool Max Size should be smaller than number of connections database can support
Waiting for free connection to become available is OK
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Law of Gravity
•Shitty Application at scale will bring down any Database
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Scale Matters
Developing and Testing with Toy Database is risky
Queries Do not slow down linearly
The slowest query may slow down most rapidly
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Memory or Disk
Data Accessed in memory is much faster than on disk
It is true even with modern SSDs
SSD accesses data in large blocks, memory does not
Fitting data in Working Set
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Newer is not Always Faster
Upgrading to the new Software/Hardware is not always
fasterTest it out Defaults Change are often to blame
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Upgrades are needed but not seamless
Major Database Upgrades often require application changes
Having Conversation on Application Lifecycle is a key
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Character Sets
Performance Impact
Pain to Change
Wrong Character Set can cause Data Loss
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Character Sets
https://per.co.na/MySQLCharsetImpact
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Less impact In MySQL 8
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Operational Overhead
Operations Take Time, Cost Money, Cause Overhead
10TB Database Backup ?
Adding The Index to Large Table ?
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Distributed Systems
10x+ More Complicated
Better High Availability
Many Failure Scenarios
Test how application performs
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Risks of Automation
Automation is Must Mistakes can destroy database at scale
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Security
Database is where the most sensitive data tends to live
Shared Devs and Ops Responsibility
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What Else
•What Would you Add ?
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Thank You!Twitter: @percona @peterzaitsev