Compaction, Compaction Everywhere

Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

SOUTH BAY CASSANDRA USERS NOVEMBER 2014

COMPACTION, COMPACTION, EVERYWHERE.

Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

Aaron Morton@aaronmorton

Co-Founder & Principal Consultant

About The Last Pickle.

Work with clients to deliver and improve Apache Cassandra based solutions.

Apache Cassandra Committer, DataStax MVP, Apache

Usergrid Committer. Based in New Zealand & USA.

Compaction?STCSLCS

DTCS

Compaction?

Because reasons.

No compaction?

Row fragmentation would result in dramatically increased

read latency.

No compaction?

Increased file count would increase memory usage.

No compaction?

Overwrites and deletions would result in wasted disk

space.

Compaction?

Yes.

Compaction?

Log Structured Merge Tree.

Compaction?

Creating new files when flushing to disk improves performance and reduces

complexity.

Compaction?

SSTable 1foo: dishwasher (ts 10): tomato purple (ts 10): cromulent

SSTable 2foo: frink (ts 20): flayven monkey (ts 10): embiggins

SSTable 3 SSTable 4foo: dishwasher (ts 15): tomacco

SSTable 5

Demo.

nodetool cfhistograms foo bar

SSTables per Read 1 sstables: 149 2 sstables: 62 3 sstables: 65 4 sstables: 50 5 sstables: 45 6 sstables: 44 7 sstables: 76 8 sstables: 72 10 sstables: 305 12 sstables: 390

Compaction?STCSLCS

DTCS

SizeTieredCompactionStrategy

The first compaction strategy.

Group files of a similar size for compaction.

SizeTieredCompactionStrategy

Works well when data is written to initially and then

only read from.

STCS - After flush.

Tier 0 ( < 50 MB) Tier 1 ~125MB

STCS - Compaction Starts

Tier 0 ( < 50 MB) Tier 1 ~125MB

STCS - New SSTable

Tier 0 ( < 50 MB) Tier 1 ~125MB

STCS - Purge old SSTables

Tier 0 ( < 50 MB) Tier 1 ~125MB

STCS - Compaction Starts (again)

Tier 0 ( < 50 MB) Tier 1 ~125MB

STCS - Final State

Tier 0 ( < 50 MB) Tier 1 ~200MB Tier 2 ~800MB

Maximum size of SSTables in the “small” bucket.

Default 50

STCS - min_sstable_size

Lower bound of the bucket size compared to the average

size in the bucket. Default 0.5

STCS - bucket_low

Upper bound of the bucket size compared to the average

size in the bucket. Default 1.5

STCS - bucket_high

Maximum percentage of reads SSTables ignored by STCS may

be responsible for.Default 0

STCS - cold_reads_to_omit

Compact buckets with at least this many SSTables.

Default 4

min_compaction_threshold

Compact no more than this many SSTables in a bucket.

Default 32

max_compaction_threshold

Compaction?STCSLCS

DTCS

LeveledCompactionStrategy

Based on LevelDB from the Chromium team.

http://leveldb.org/

LeveledCompactionStrategy

Works well with overwrites and tombstones.

Provides low read latency.

LeveledCompactionStrategy

“Uses twice the disk IO”

DataStax Blogs

“Leveled Compaction in Apache Cassandra”

“When to Use Leveled Compaction”

LCS - “It’s going to be all levels Jerry”

Level Number of Files

0 Unlimited*1 1002 10003 10000

LCS in nodetool cfstats

Column Family: HappyPandaCF SSTable count: 21 SSTables in each level: [1, 7, 13, 0, 0, 0, 0, 0, 0]

Column Family: SadPandaCF SSTable count: 710 SSTables in each level: [1, 10, 117/100, 582, 0, 0, 0, 0, 0]

LCS - Starting out

level 0

LCS - New File in Level 1

level 0 level 1

LCS - Later, Compact L0 With Overlapping L1

level 1level 0

LCS - Another File in L1

level 0 level 1

LCS - Level 1 Full, compact overlapping

level 0 level 1

LCS - New Files in Level 2

level 0 level 1 level 2

Maximum* size of each SSTable at all levels.

Default 160

LCS - sstable_size_in_mb

Compaction?STCSLCS

DTCS

DateTieredCompactionStrategy

CASSANDRA-6602

In 2.0.11 and 2.1.1“Experimental”

DTCS - Compact Newest Time Bucket

80 hours > 365 days20 hours4 hours

DTCS - New File in First Bucket

80 hours > 365 days20 hours4 hours

DTCS - Promoted to Later Bucket

80 hours > 365 days20 hours4 hours

Target size.

Multiplied by min_sstable_size.

DTCS - base_time_seconds

What TimeUnit you are using for your WriteTime.

DTCS - timestamp_resolution

Do not compact SSTables where the youngest

WRITETIME is older than this.

DTCS - max_sstable_age_days

Thanks.

Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

Aaron Morton@aaronmorton

Co-Founder & Principal Consultantwww.thelastpickle.com

Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License