hbase compaction

http://hbase.apache.org/book/regions.arch.html#compaction

http://hbase.apache.org/book/

http://hbase.apache.org/book.html

摘：

9.7.5.5.1. Compaction File Selection

To understand the core algorithm for StoreFile selection, there is some ASCII-art in the Store source code that will serve as useful reference. It has been copied below:

/* normal skew:
 *
 *         older ----> newer
 *     _
 *    | |   _
 *    | |  | |   _
 *  --|-|- |-|- |-|---_-------_-------  minCompactSize
 *    | |  | |  | |  | |  _  | |
 *    | |  | |  | |  | | | | | |
 *    | |  | |  | |  | | | | | |
 */

Important knobs:

• hbase.store.compaction.ratio Ratio used in compaction file selection algorithm (default 1.2f).
• hbase.hstore.compaction.min (.90 hbase.hstore.compactionThreshold) (files) Minimum number of StoreFiles per Store to be selected for a compaction to occur (default 2).
• hbase.hstore.compaction.max (files) Maximum number of StoreFiles to compact per minor compaction (default 10).
• hbase.hstore.compaction.min.size (bytes) Any StoreFile smaller than this setting with automatically be a candidate for compaction. Defaults to hbase.hregion.memstore.flush.size (128 mb).
• hbase.hstore.compaction.max.size (.92) (bytes) Any StoreFile larger than this setting with automatically be excluded from compaction (default Long.MAX_VALUE).

The minor compaction StoreFile selection logic is size based, and selects a file for compaction when the file <= sum(smaller_files) *hbase.hstore.compaction.ratio.

9.7.5.5.2. Minor Compaction File Selection - Example #1 (Basic Example)

This example mirrors an example from the unit test TestCompactSelection.

• hbase.store.compaction.ratio = 1.0f
• hbase.hstore.compaction.min = 3 (files)
• hbase.hstore.compaction.max = 5 (files)
• hbase.hstore.compaction.min.size = 10 (bytes)
• hbase.hstore.compaction.max.size = 1000 (bytes)

The following StoreFiles exist: 100, 50, 23, 12, and 12 bytes apiece (oldest to newest). With the above parameters, the files that would be selected for minor compaction are 23, 12, and 12.

Why?

• 100 --> No, because sum(50, 23, 12, 12) * 1.0 = 97.
• 50 --> No, because sum(23, 12, 12) * 1.0 = 47.
• 23 --> Yes, because sum(12, 12) * 1.0 = 24.
• 12 --> Yes, because the previous file has been included, and because this does not exceed the the max-file limit of 5
• 12 --> Yes, because the previous file had been included, and because this does not exceed the the max-file limit of 5.

9.7.5.5.3. Minor Compaction File Selection - Example #2 (Not Enough Files To Compact)

This example mirrors an example from the unit test TestCompactSelection.

• hbase.store.compaction.ratio = 1.0f
• hbase.hstore.compaction.min = 3 (files)
• hbase.hstore.compaction.max = 5 (files)
• hbase.hstore.compaction.min.size = 10 (bytes)
• hbase.hstore.compaction.max.size = 1000 (bytes)

The following StoreFiles exist: 100, 25, 12, and 12 bytes apiece (oldest to newest). With the above parameters, the files that would be selected for minor compaction are 23, 12, and 12.

Why?

• 100 --> No, because sum(25, 12, 12) * 1.0 = 47
• 25 --> No, because sum(12, 12) * 1.0 = 24
• 12 --> No. Candidate because sum(12) * 1.0 = 12, there are only 2 files to compact and that is less than the threshold of 3
• 12 --> No. Candidate because the previous StoreFile was, but there are not enough files to compact

9.7.5.5.4. Minor Compaction File Selection - Example #3 (Limiting Files To Compact)

This example mirrors an example from the unit test TestCompactSelection.

• hbase.store.compaction.ratio = 1.0f
• hbase.hstore.compaction.min = 3 (files)
• hbase.hstore.compaction.max = 5 (files)
• hbase.hstore.compaction.min.size = 10 (bytes)
• hbase.hstore.compaction.max.size = 1000 (bytes)

The following StoreFiles exist: 7, 6, 5, 4, 3, 2, and 1 bytes apiece (oldest to newest). With the above parameters, the files that would be selected for minor compaction are 7, 6, 5, 4, 3.

Why?

• 7 --> Yes, because sum(6, 5, 4, 3, 2, 1) * 1.0 = 21. Also, 7 is less than the min-size
• 6 --> Yes, because sum(5, 4, 3, 2, 1) * 1.0 = 15. Also, 6 is less than the min-size.
• 5 --> Yes, because sum(4, 3, 2, 1) * 1.0 = 10. Also, 5 is less than the min-size.
• 4 --> Yes, because sum(3, 2, 1) * 1.0 = 6. Also, 4 is less than the min-size.
• 3 --> Yes, because sum(2, 1) * 1.0 = 3. Also, 3 is less than the min-size.
• 2 --> No. Candidate because previous file was selected and 2 is less than the min-size, but the max-number of files to compact has been reached.
• 1 --> No. Candidate because previous file was selected and 1 is less than the min-size, but max-number of files to compact has been reached.

9.7.5.5.5. Impact of Key Configuration Options

hbase.store.compaction.ratio. A large ratio (e.g., 10) will produce a single giant file. Conversely, a value of .25 will produce behavior similar to the BigTable compaction algorithm - resulting in 4 StoreFiles.

hbase.hstore.compaction.min.size. Because this limit represents the "automatic include" limit for all StoreFiles smaller than this value, this value may need to be adjusted downwards in write-heavy environments where many 1 or 2 mb StoreFiles are being flushed, because every file will be targeted for compaction and the resulting files may still be under the min-size and require further compaction, etc.