big data & postgresql - using tablesample to analyze very large datasets
TRANSCRIPT
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Big Data & PostgreSQLUsing TABLESAMPLE to Analyze
Very Large Datasets
By Umair Shahid
© 2ndQuadrant 2016
Who am I?Got “pushed” into PostgreSQL in 2004, ended up
falling in love with itNot a hardcore techie, yet passionate about open
source softwareHeading the productization efforts at 2ndQuadrantInterested in Big Data, specifically the newer
PostgreSQL features supporting it
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What is the problem?Number of Rows Size on Disk (MB) Time Taken (ms)
1k 0.23 219.706
100k 24 1,302.135
1M 195 7,696.386
5M 951 40,691.603
10M 1,923 60,012.457
100M 19,456 801,493.319
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Why is this significant?Data mining has typically been a painful processMajor contributor to the pain has been the time it
takes for queries to returnMany false steps before the required data is
identifiedWaiting time is wasted timeSampling, count based or time based, reduces the
wasted time significantly
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What is TABLESAMPLE?
Ability to read a random sample of data in a table
Defined in SQL:2003 (5th revision of SQL)
Implemented in PostgreSQL 9.5
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Syntax
SELECT select_expression
FROM table_name
TABLESAMPLE sampling_method ( argument [, ...] )
[ REPEATABLE ( seed ) ]
...
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sampling_methodargument is percentage of rowsSYSTEM
Block level samplingVery fastNon-independent rows
BERNOULLIRow level samplingSlower than SYSTEMIndependent rows (uniformly random)
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Demo sampling methods
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REPEATABLE results(Reminder: [ REPEATABLE ( seed ) ])
Optional argumentUsed if random, yet repeatable results are
requiredseed and argument need to be the same to
produce repeatable resultsAny changes made to the table will result in a
different data set
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Now it gets interesting … TABLESAMPLE allows for additional sampling methods via
extensionstsm_system_time specifies max number of milliseconds
to spend reading a tableImplements the syntax:
SELECT select_expression
FROM table_name
TABLESAMPLE SYSTEM_TIME (argument)
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Demo tsm_system_time
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Enter Orange ...Funded by AXLE (
http://axleproject.eu)Same project funded
TABLESAMPLEAvailable integrated with
PostgreSQL in 2UDA (http://2ndquadrant.com/2uda)
Uses TABLESAMPLE to very quickly create visualizations for data
Can quickly create predictive models
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Demo OrangeYou can find a very helpful tutorial at
http://2ndquadrant.com/2uda
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Other Big Data features in PostgreSQL
JSON & JSONBHSTOREXMLScale-out by partitioning
Check out Postgres-XL (http://www.postgres-xl.org/)
etc ...
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Umair ShahidEmail: [email protected]
Twitter: @pg_umair
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