9.2. Catalog Tables

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.

9.2.1. -ROOT-


The -ROOT- table was removed in HBase 0.96.0. Information here should be considered historical.

The -ROOT- table kept track of the location of the .META table (the previous name for the table now called hbase:meta) prior to HBase 0.96. The -ROOT- table structure was as follows:


  • .META. region key (.META.,,1)


  • info:regioninfo (serialized HRegionInfo instance of hbase:meta)

  • info:server (server:port of the RegionServer holding hbase:meta)

  • info:serverstartcode (start-time of the RegionServer process holding hbase:meta)

9.2.2. hbase:meta

The hbase:meta table (previously called .META.) keeps a list of all regions in the system. The location of hbase:meta was previously tracked within the -ROOT- table, but is now stored in Zookeeper.

The hbase:meta table structure is as follows:


  • Region key of the format ([table],[region start key],[region id])


  • info:regioninfo (serialized HRegionInfo 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 Writables utility.

9.2.3. 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 Section 9.7.2, “Region-RegionServer Assignment”.

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