Techniques for Measuring Data Size in OceanBase at Server, Tenant, and Table Levels

OceanBase is a multi‑tenant distributed database, and when measuring data size one must consider multiple tenants and replicas on a single server, as well as the fact that data files on disk are pre‑allocated.

1 Server‑level Statistics

The OCP "Cluster Overview" shows each OBServer's total and used disk capacity, allowing a quick view of overall cluster usage. For example, a server displaying 2.5TB/16.8TB means the pre‑allocated datafile_size (or datafile_disk_percentage) is 16.8 TB, while the actual data stored in block_file is 2.5 TB.

Disk usage can also be obtained directly from the OS:

df -h |grep /data/1
Filesystem             Size  Used Avail Use% Mounted on
/dev/mapper/observervg-obdata   24T   17T  7.1T  71% /data/1

ll /data/1/group_x86_pt01/sstable/
total 17T
-rw-r----- 1 admin admin 17T Jan 18 01:31 block_file

The view __all_virtual_disk_stat provides the same information without OCP. The following query works on both V3 and V4 (run in the sys tenant):

SELECT
  svr_ip,
  svr_port,
  total_size / 1024 / 1024 / 1024 AS total_size_GB,
  free_size  / 1024 / 1024 / 1024 AS free_size_GB,
  (total_size - free_size) / 1024 / 1024 / 1024 AS used_size_GB
FROM __all_virtual_disk_stat;

2 Tenant‑level Statistics

Tenant‑level statistics are more meaningful for data‑size analysis because a tenant corresponds to a MySQL/Oracle instance and may have multiple replicas across zones.

For V3 (run in sys tenant):

select
  zone,
  svr_ip,
  svr_port,
  sum(data_size) / 1024 / 1024 / 1024 as data_size_gb,
  sum(required_size) / 1024 / 1024 / 1024 as required_size_gb
from __all_virtual_meta_table
where tenant_id = 1001
group by zone, svr_ip, svr_port;

For V4 the query uses CDB_OB_TABLET_REPLICAS:

--
select
  svr_ip,
  svr_port,
  sum(data_size) / 1024 / 1024 / 1024 as data_size_gb,
  sum(required_size) / 1024 / 1024 / 1024 as required_size_gb
from CDB_OB_TABLET_REPLICAS
where TENANT_ID = 1004
group by svr_ip, svr_port;

Key observations from the example:

Tenant 1001 has three zones (three replicas).

Each replica stores about 2.3 TB of real data ( data_size_gb) and requires about 2.6 TB of disk space ( required_size_gb).

The Oracle‑mode statistics can also be obtained via DBA_SEGMENTS in the business tenant.

3 Table‑level Statistics

To get the size of a specific table, use the DBA_SEGMENTS view in Oracle mode:

select
  owner,
  segment_name,
  round(bytes / 1024 / 1024, 2) as "SIZE(M)"
from DBA_SEGMENTS
where segment_name = 'ETL_P10IDS_RISKCON' and owner = 'LIFE';

In the sys tenant the equivalent query is:

select
  meta.zone,
  meta.svr_ip,
  t.database_name,
  t.table_name,
  round(meta.data_size / 1024 / 1024, 2) as "DATA_SIZE(M)",
  round(meta.required_size / 1024 / 1024, 2) as "REQUIRED_SIZE(M)"
from __all_virtual_meta_table meta
join gv$table t on meta.table_id = t.table_id
where t.table_name = 'ETL_P10IDS_RISKCON' and t.database_name = 'LIFE';

For V4, table and index sizes can be aggregated separately:

select y.SVR_IP, y.DATABASE_NAME,
       case when y.TABLE_TYPE = 'INDEX' then '' else y.TABLE_NAME end as TABLE_NAME,
       y.TABLE_TYPE,
       sum(y.DATA_SIZE) as "DATA_SIZE(MB)",
       sum(y.REQUIRED_SIZE) as "REQUIRED_SIZE(MB)"
from (
  select a.TENANT_ID, a.SVR_IP, a.TABLET_ID, b.table_id, b.DATABASE_NAME, b.TABLE_NAME, b.TABLE_TYPE,
         round(a.data_size/1024/1024,2) as DATA_SIZE,
         round(a.required_size/1024/1024,2) as REQUIRED_SIZE
  from CDB_OB_TABLET_REPLICAS a
  join cdb_ob_table_locations b on a.TABLET_ID=b.TABLET_ID and a.svr_ip=b.svr_ip and a.tenant_id=b.tenant_id
  where a.TENANT_ID=1004 and b.DATABASE_NAME='test' and (
        b.TABLE_NAME='sbtest3' or
        b.DATA_TABLE_ID in (select table_id from cdb_ob_table_locations where TENANT_ID=1004 and TABLE_NAME='sbtest3')
      )
) y
group by y.SVR_IP, y.DATABASE_NAME, y.TABLE_TYPE
order by y.SVR_IP, y.DATABASE_NAME asc, TABLE_NAME desc;

The agile diagnostic tool obdiag can also report table size, but it only counts one follower replica and does not include the require_data_size on disk. A known bug (now fixed) caused partitioned tables to report only a single partition's size.

Example command:

obdiag gather tabledump --user=root@my#hucq_421 --password='aaBB11@@' --database=test --table=sbtest3

Overall, the article provides practical SQL snippets and tooling tips to accurately measure OceanBase data size at different granularities, helping administrators and developers understand storage consumption and plan capacity.