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https://issues.apache.org/jira/browse/HBASE-3842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13061614#comment-13061614
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Andrew Purtell commented on HBASE-3842:
---------------------------------------
Additionally I propose the addition of a new coprocessor observer type,
{{CompactionObserver}}, with the following interface:
{code}
/**
* Notification that compaction is about to begin.
* @param context Observer context
* @param store the Store that is about to be compacted
* @return false to skip compaction
*/
boolean preCompact(ObserverContext<~> context, Store store);
/**
* Notification that compaction completed
* @param context Observer context
* @param store the Store that was compacted
*/
void postCompact(ObserverContext<~> context, Store store);
/**
* Called before a KV is written to the new store file.
* <p>
* WARNING: It is only safe, unless you <i>really</i> know what you are doing,
* to signal the KV should be dropped by returning {{null}} or to return a KV
* with only the value changed somehow.
* @param context Observer context
* @param store the Store that is being compacted
* @param kv the KeyValue
* @return the KeyValue to write, or null if none
*/
KeyValue preCompactWrite(ObserverContext<~> context, Store store, KeyValue kv);
/**
* Called after a KV is written to the new store file.
* @param context Observer context
* @param store the Store that is being compacted
* @param kv the KeyValue
*/
void postCompactWrite(ObserverContext<~> context, Store store, KeyValue kv);
{code}
If the coprocessor implements this interface, it is hooked into the compaction
process such that it can operate on every KV. This is the same model we use for
WAL observers.
> Refactor Coprocessor Compaction API
> -----------------------------------
>
> Key: HBASE-3842
> URL: https://issues.apache.org/jira/browse/HBASE-3842
> Project: HBase
> Issue Type: Improvement
> Components: coprocessors, regionserver
> Affects Versions: 0.92.0
> Reporter: Nicolas Spiegelberg
> Assignee: Nicolas Spiegelberg
> Labels: compaction
> Fix For: 0.92.0
>
>
> After HBASE-3797, the compaction logic flow has been significantly altered.
> Because of this, the current compaction coprocessor API is insufficient for
> gaining full insight into compaction requests/results. Refactor coprocessor
> API after HBASE-3797 is committed to be more extensible and increase
> visibility.
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