# Preparing to update the time zone file
<a name="Appendix.Oracle.Options.Timezone-file-autoupgrade.preparing"></a>

A time zone file upgrade has two separate phases: prepare and upgrade. While not required, we strongly recommend that you perform the prepare step. In this step, you find out which data will be affected by running the PL/SQL procedure `DBMS_DST.FIND_AFFECTED_TABLES`. For more information about the prepare window, see [Upgrading the Time Zone File and Timestamp with Time Zone Data](https://docs.oracle.com/en/database/oracle/oracle-database/19/nlspg/datetime-data-types-and-time-zone-support.html#GUID-B0ACDB2E-4B49-4EB4-B4CC-9260DAE1567A) in the Oracle Database documentation.

**To prepare to update the time zone file**

1. Connect to your Oracle database using a SQL client.

1. Determine the current timezone file version used.

   ```
   SELECT * FROM V$TIMEZONE_FILE;
   ```

1. Determine the latest timezone file version available on your DB instance.

   ```
   SELECT DBMS_DST.GET_LATEST_TIMEZONE_VERSION FROM DUAL;
   ```

1. Determine the total size of tables that have columns of type `TIMESTAMP WITH LOCAL TIME ZONE` or `TIMESTAMP WITH TIME ZONE`.

   ```
   SELECT SUM(BYTES)/1024/1024/1024 "Total_size_w_TSTZ_columns_GB"
   FROM   DBA_SEGMENTS
   WHERE  SEGMENT_TYPE LIKE 'TABLE%'
   AND    (OWNER, SEGMENT_NAME) IN
            (SELECT OWNER, TABLE_NAME
             FROM   DBA_TAB_COLUMNS
             WHERE  DATA_TYPE LIKE 'TIMESTAMP%TIME ZONE');
   ```

1. Determine the names and sizes of segments that have columns of type `TIMESTAMP WITH LOCAL TIME ZONE` or `TIMESTAMP WITH TIME ZONE`.

   ```
   SELECT OWNER, SEGMENT_NAME, SUM(BYTES)/1024/1024/1024 "SEGMENT_SIZE_W_TSTZ_COLUMNS_GB"
   FROM   DBA_SEGMENTS
   WHERE  SEGMENT_TYPE LIKE 'TABLE%'
   AND    (OWNER, SEGMENT_NAME) IN
            (SELECT OWNER, TABLE_NAME
             FROM   DBA_TAB_COLUMNS
             WHERE  DATA_TYPE LIKE 'TIMESTAMP%TIME ZONE')
   GROUP BY OWNER, SEGMENT_NAME;
   ```

1. Run the prepare step. 
   + The procedure `DBMS_DST.CREATE_AFFECTED_TABLE` creates a table to store any affected data. You pass the name of this table to the `DBMS_DST.FIND_AFFECTED_TABLES` procedure. For more information, see [CREATE\$1AFFECTED\$1TABLE Procedure](https://docs.oracle.com/en/database/oracle/oracle-database/19/arpls/DBMS_DST.html#GUID-C53BAABA-914A-404C-9CD5-823257BE0B00) in the Oracle Database documentation.
   + This procedure `CREATE_ERROR_TABLE` creates a table to log errors. For more information, see [CREATE\$1ERROR\$1TABLE Procedure](https://docs.oracle.com/en/database/oracle/oracle-database/19/arpls/DBMS_DST.html#GUID-6A7EA024-B02D-4486-B1D6-EF6ABF5DE507) in the Oracle Database documentation.

   The following example creates the affected data and error tables, and finds all affected tables.

   ```
   EXEC DBMS_DST.CREATE_ERROR_TABLE('my_error_table')
   EXEC DBMS_DST.CREATE_AFFECTED_TABLE('my_affected_table')
   
   EXEC DBMS_DST.BEGIN_PREPARE(new_version);
   EXEC DBMS_DST.FIND_AFFECTED_TABLES('my_affected_table', TRUE, 'my_error_table');
   EXEC DBMS_DST.END_PREPARE;
   
   SELECT * FROM my_affected_table;
   SELECT * FROM my_error_table;
   ```

1. Query the affected and error tables.

   ```
   SELECT * FROM my_affected_table;
   SELECT * FROM my_error_table;
   ```