Catalog Tables
Understanding hbase:meta catalog table structure, location tracking, and how HBase maintains region metadata.
The catalog table hbase:meta exists as an HBase table and is filtered out of the HBase shell's list command, but is in fact a table just like any other.
hbase:meta
The hbase:meta table (previously called .META.) keeps a list of all regions in the system, and the location of hbase:meta is stored in ZooKeeper.
The hbase:meta table structure is as follows:
Key:
- Region key of the format (
[table],[region start key],[region id])
Values:
info:regioninfo(serialized RegionInfo instance for this region)info:server(server:port of the RegionServer containing this region)info:serverstartcode(start-time of the RegionServer process containing this region)
When a table is in the process of splitting, two other columns will be created, called info:splitA and info:splitB. These columns represent the two daughter regions. The values for these columns are also serialized HRegionInfo instances. After the region has been split, eventually this row will be deleted.
Note on HRegionInfo
The empty key is used to denote table start and table end. A region with an empty start key is the first region in a table. If a region has both an empty start and an empty end key, it is the only region in the table
In the (hopefully unlikely) event that programmatic processing of catalog metadata is required, see the RegionInfo.parseFrom utility.
Startup Sequencing
First, the location of hbase:meta is looked up in ZooKeeper. Next, hbase:meta is updated with server and startcode values.
For information on region-RegionServer assignment, see Region-RegionServer Assignment.