accumulo summit 2015: accumulo in-depth: building bulk ingest [sponsored]
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Building Bulk ImportEric Newton
SW Complete, Inc.
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Ingest 101
The life of a mutation: Send to server Write to Write-Ahead Log Store in memory Write memory to a file Merge, re-write as needed
At least two writes, small in-memory sort
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Bulk Ingest
Accumulo: heavy ingest Use Map-Reduce efficiency Pre-sort incoming data Hand whole sorted files to accumulo One write Larger sorts
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Version 1
importDirectory(String dir, String failDir)Client computes the servers that need the file:
Analysis of file Moves directory under Accumulo Retry logic (to handle splits, failures)
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Version 1: problems
Limited to the clients computational power Permission: client had to be all-knowing Files could be added to servers many times Defer file collection while bulk importing Clients can fail
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Version 1.1
Clients hand bulk imports to the master Fixed permission problems Added a bulk import test to the Random
Walk test suit
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The Test
Create a sorted file with a lot of 1s:12345678 -> 1
Create an identical file, with lots of -1s:12345678 -> -1
Add a summation iterator over the tableVerify: every entry should be zero:
12345678 -> 0
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Random Walk 101
Randomly: Import files in random order Split the files into random sizes Split tablets and random points Kill tablet servers (agitate)
Under loadAt scale
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Version 2.0
Master only coordinates file processing Distribute work to tablet servers Master distributes files to tablet servers Tablet serves
Analyze files for assignments Retry Communicate with destination tablet servers
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FilesFilesFiles
Command Flow
Client Master TabletServer
TabletServer
TabletServer
TabletServer
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Problems
Problems solved: Permissions controlled by Master File processing is distributed
Bulk import tested heavilyConsistency
Not so much
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Version 3.0
Problem: file imported more than once Repeated reloading RPC timeouts Tablet migration Tablet split
Add flags to metadata table to prevent: file garbage collection repeated imports
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Version 3.0
Problem Solved Reduced Name Node ops Reduced trash laying around from failed imports Imports not repeated
Does it stand up to the Random Walk Test? Not so much
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Death by Slow ThreadPlease take this file
OK looks good, never saw this beforeSleep
Hey, Please take this file, againOK looks good, never saw this beforeThanks!Compact!Wakeup! Time to import that file from the 1st request!
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Zookeeper to the Rescue
Add a 3rd party negotiator Define a session Add a file only while session is active Store session in zookeeper Get agreement about the session at each critical point,
including metadata table updatesSession guides clean-up of markersSession closes only after all agree
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Session
Take this file, for session 123OK, working on session 123Never saw this file beforeSleep
Repeat, file for session 123Never saw this file before
Anybody working on session 123?
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Session
Yes, Im processing session 123!OK, finish up.
Double check on session 123, import fileAnybody working on session 123?
Whats session 123?Remove markers in metadata
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Bulk Import
Problem solved: Distributed processing Permissions Files imported once, and only once Markers are cleaned up in the face of failures
Performance Not so much
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Master as BottleneckBulk import thousands of filesEvery 15 minutesMaster renames files and puts them under /accumulo
BottleneckOne master competes for NN ops with N tablet servers
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Master, Go Faster
Add configurable thread poolPush more move requests to the NNCompete more fiercely for resources
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Bulk Import
More efficient data ingestEasy: just a file to the right tabletsHard: consistency in a distributed systemTesting is your friendNothing prepares you for large-scale problems!