static long getNamespaceSnapshotSize(Connection conn, String namespace) throws IOException {
    try (Table quotaTable = conn.getTable(QuotaTableUtil.QUOTA_TABLE_NAME)) {
      Result r = quotaTable.get(createGetNamespaceSnapshotSize(namespace));
      if (r.isEmpty()) {
        return 0L;
      }
      r.advance();
      return parseSnapshotSize(r.current());
    } catch (InvalidProtocolBufferException e) {
      throw new IOException("Could not parse snapshot size value for namespace " + namespace, e);
    }
  }
Fetches the computed size of all snapshots against tables in a namespace for space quotas.
hbase-client/src/main/java/org/apache/hadoop/hbase/quotas/QuotaTableUtil.java