[opentsdb] hbase uid 스키마에서 특이한 점 - 마지막 저장 위치를 0x00에서 저장

opentsdb의 hbase 스키마는 다음 url에서 확인할 수 있다.

특이한 점은 데이터는 역순(증분)으로 되어 있고 마지막 uid 정보를 0x00에 저장한다는 점이다. 

따라서 scanning할 때 무척 편하게 할 수 있다. 

http://opentsdb.net/docs/build/html/user_guide/backends/hbase.html

UID Table Schema

A separate, smaller table called tsdb-uid stores UID mappings, both forward and reverse. Two columns exist, one named name that maps a UID to a string and another id mapping strings to UIDs. Each row in the column family will have at least one of three columns with mapping values. The standard column qualifiers are:

• metrics for mapping metric names to UIDs
• tagk for mapping tag names to UIDs
• tagv for mapping tag values to UIDs.

The name family may also contain additional meta-data columns if configured.

id Column Family

Row Key - This will be the string assigned to the UID. E.g. for a metric we may have a value of sys.cpu.user or for a tag value it may be 42.

Column Qualifiers - One of the standard column types above.

Column Value - An unsigned integer encoded on 3 bytes by default reflecting the UID assigned to the string for the column type. If the UID length has been changed in the source code, the width may vary.

name Column Family

Row Key - The unsigned integer UID encoded on 3 bytes by default. If the UID length has been changed in the source code, the width may be different.

Column Qualifiers - One of the standard column types above OR one of metrics_meta, tagk_meta or tagv_meta.

Column Value - For the standard qualifiers above, the string assigned to the UID. For a *_meta column, the value will be a UTF-8 encoded, JSON formatted UIDMeta Object as a string. Do not modify the column value outside of OpenTSDB. The order of the fields is important, affecting CAS calls.

UID Assignment Row

Within the id column family is a row with a single byte key of \x00. This is the UID row that is incremented for the proper column type (metrics, tagk or tagv) when a new UID is assigned. The column values are 8 byte signed integers and reflect the maximum UID assigned for each type. On assignment, OpenTSDB calls HBase's atomic increment command on the proper column to fetch a new UID.