long getPreviousNamespaceSnapshotSize(Table quotaTable, String namespace) throws IOException {
    // Update the size of each snapshot for all snapshots in a namespace.
    Result r = quotaTable.get(QuotaTableUtil.createGetNamespaceSnapshotSize(namespace));
    return getSnapshotSizeFromResult(r);
  }
Fetches the current size of all snapshots in the given {@code namespace}.
@param quotaTable The HBase quota table
@param namespace  Namespace to fetch the sum of snapshot sizes for
@return The size of all snapshot sizes for the namespace in bytes.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/FileArchiverNotifierImpl.java