hbase里面对一行操作前会加锁。
http://hadoop-hbase.blogspot.com/2012/01/hbase-intra-row-transactions.html
https://issues.apache.org/jira/browse/HBASE-3584
HBASE-3584的功能是对同一行的Put和Delete可以原子性的完成。
Delete：
put 't1', 'r1', 'f1:c', 'aaa', 1
put 't1', 'r1', 'f1:c', 'bbb', 2
put 't1', 'r1', 'f1:c', 'ccc', 3
delete 't1','r1','f1:c', 3 这个会把前面3条数据都删除掉。
scan 't1'
scan 't1', {RAW => true, VERSIONS => 10}
Deletes work by creating tombstone markers. For example, let's suppose we want to delete a row. For this you can specify a version, or else by default the currentTimeMillis is used. What this means is “delete all cells where the version is less than or equal to this version”.
Memstore flush的时候，应该删除的put会被过滤掉，不写入HFile。Delete marker在major compact的时候删除。
https://issues.apache.org/jira/browse/HBASE-4536
https://issues.apache.org/jira/browse/HBASE-4071
https://issues.apache.org/jira/browse/HBASE-4241
region太大的问题是大compact的时候会影响正常读写。
Region做compact的时候是一个个cf来做的。
https://wiki.trafodion.org/wiki/index.php/Main_Page
The main practical difference is that only a major compaction cleans out delete markers.
Delete markers cannot be removed during a minor compaction since an affected KeyValue could exist in an HFile that is not part of this compaction.
Delete只在major_compact的时候删除掉
Memstore flush的时候会去除无用的数据
minor compaction的时候也会删除无用的数据