Partitioning -- 13d : TRUNCATE and DROP Partitions and Global Indexes

A TRUNCATE or DROP Partition makes Global Indexes on a Partitioned Table UNUSABLE.

You may be lucky if the target partition was empty, resulting in Oracle maintaining Global Indexes as valid.  However, the accepted rule is that you either (a) use the UPDATE INDEXES clause [resulting in the TRUNCATE or DROP taking longer to run, effectively locking the table partitions] OR  (b) do a REBUILD of the Indexes that become UNUSABLE after the TRUNCATE or DROP.

12c has introduced what it calls Asynchronous Global Index Maintenance.  With this feature present, the TRUNCATE or DROP runs much faster as a DDL without actually removing the target rows from the Global Indexes [but still requires the UPDATE INDEXES clause to be specified]

So, now in my 12.2 database I have these two Indexes on SALES_DATA :

SQL> select index_name, partitioned, status
  2  from user_indexes
  3  where table_name = 'SALES_DATA'
  4  order by 2,1
  5  /

INDEX_NAME                     PAR STATUS
------------------------------ --- --------
SALES_DATA_PK                  NO  VALID
SALES_DATA_LCL_NDX_1           YES N/A

SQL> 

I then TRUNCATE a non-empty Partition and check the Indexes

SQL> alter table sales_data truncate partition P_2015 update indexes;

Table truncated.

SQL>
SQL> select index_name, partitioned, status, orphaned_entries
  2  from user_indexes
  3  where table_name = 'SALES_DATA'
  4  order by 2,1
  5  /

INDEX_NAME                     PAR STATUS   ORP
------------------------------ --- -------- ---
SALES_DATA_PK                  NO  VALID    YES
SALES_DATA_LCL_NDX_1           YES N/A      NO

SQL> 

The ORPHANED_ENTRIES column indicates that SALES_DATA_PK is subject to Asynchronous Index Maintenance.

This is the job that will do the Index Maintenance at 2am  :

SQL> l
  1  select owner, job_name, last_start_date, next_run_Date
  2  from dba_scheduler_jobs
  3* where job_name = 'PMO_DEFERRED_GIDX_MAINT_JOB'
SQL> /

OWNER
---------------------------------------------------------------------------
JOB_NAME
---------------------------------------------------------------------------
LAST_START_DATE
---------------------------------------------------------------------------
NEXT_RUN_DATE
---------------------------------------------------------------------------
SYS
PMO_DEFERRED_GIDX_MAINT_JOB
20-MAR-19 10.18.51.215433 AM UTC
21-MAR-19 02.00.00.223589 AM UTC


SQL> !date
Wed Mar 20 20:05:24 SGT 2019

SQL> 

So, I could
(1) wait for the next run of the job OR
(2) manually trigger the job (which will scan the entire database for all indexes that require such maintenance) OR
(3) Execute  DBMS_PART.CLEANUP_GIDX  to initiate the maintenance for the specific index OR
(4) Execute an ALTER INDEX REBUILD to make the Index USABLE again.

SQL> execute dbms_part.cleanup_gidx('HEMANT','SALES_DATA');

PL/SQL procedure successfully completed.

SQL> select index_name, partitioned, status, orphaned_entries
  2  from user_indexes
  3  where table_name = 'SALES_DATA'
  4  order by 2,1
  5  /

INDEX_NAME                     PAR STATUS   ORP
------------------------------ --- -------- ---
SALES_DATA_PK                  NO  VALID    NO
SALES_DATA_LCL_NDX_1           YES N/A      NO

SQL> 

Note that the argument to CLEANUP_GIDX is the *Table Name*, not an Index Name.


Here I have demonstrated a TRUNCATE Partition, but the same method would be usable for a DROP Partition.

Partitioning -- 13c : Merging Partitions

The reverse of SPLITting a Partition is to MERGE two adjacent partitions.

I reverse the SPLIT that I did in the previous blog post.

SQL> l
  1  select partition_name, tablespace_name, high_value
  2  from user_tab_partitions
  3  where table_name = 'SALES_DATA'
  4* order by partition_position
SQL> /

PARTITION_NAME                 TABLESPACE_NAME                HIGH_VALUE
------------------------------ ------------------------------ --------------------------
P_2016                         ARCHIVE_SALES_DATA             TO_DATE(' 2017-01-01 00:00
P_2017                         TBS_YEAR_2017                  TO_DATE(' 2018-01-01 00:00
P_2018                         TBS_YEAR_2018                  TO_DATE(' 2019-01-01 00:00
P_2019_H1                      TBS_YEAR_2019                  TO_DATE(' 2019-07-01 00:00
P_2019_H2                      TBS_YEAR_2019                  TO_DATE(' 2020-01-01 00:00
P_2020                         TBS_YEAR_2020                  TO_DATE(' 2021-01-01 00:00
P_MAXVALUE                     USERS                          MAXVALUE

7 rows selected.

SQL> 
SQL> alter table sales_data                                                  
  2  merge partitions P_2019_H1, P_2019_H2
  3  into partition P_2019
  4  update indexes
  5  /

Table altered.

SQL> 
SQL> select partition_name, tablespace_name, high_value
  2  from user_tab_partitions
  3  where table_name = 'SALES_DATA'
  4  order by partition_position
  5  /

PARTITION_NAME                 TABLESPACE_NAME                HIGH_VALUE
------------------------------ ------------------------------ --------------------------
P_2016                         ARCHIVE_SALES_DATA             TO_DATE(' 2017-01-01 00:00
P_2017                         TBS_YEAR_2017                  TO_DATE(' 2018-01-01 00:00
P_2018                         TBS_YEAR_2018                  TO_DATE(' 2019-01-01 00:00
P_2019                         HEMANT                         TO_DATE(' 2020-01-01 00:00
P_2020                         TBS_YEAR_2020                  TO_DATE(' 2021-01-01 00:00
P_MAXVALUE                     USERS                          MAXVALUE

6 rows selected.

SQL> 

But, we find that the new Partition was created in the default "HEMANT"  tablespace !  So, we have to be careful about specifying target tablespace(s).

Let me reverse the action and try again.

SQL> alter table sales_data
  2  split partition P_2019 at (to_date('01-JUL-2019','DD-MON-YYYY'))
  3  into (partition P_2019_H1 tablespace TBS_YEAR_2019, partition P_2019_H2 tablespace TBS_YEAR_2019)
  4  update indexes
  5  /

Table altered.

SQL> 
SQL> select partition_name, tablespace_name, high_value
  2  from user_tab_partitions
  3  where table_name = 'SALES_DATA'
  4  order by partition_position
  5  /

PARTITION_NAME                 TABLESPACE_NAME                HIGH_VALUE
------------------------------ ------------------------------ --------------------------
P_2016                         ARCHIVE_SALES_DATA             TO_DATE(' 2017-01-01 00:00
P_2017                         TBS_YEAR_2017                  TO_DATE(' 2018-01-01 00:00
P_2018                         TBS_YEAR_2018                  TO_DATE(' 2019-01-01 00:00
P_2019_H1                      TBS_YEAR_2019                  TO_DATE(' 2019-07-01 00:00
P_2019_H2                      TBS_YEAR_2019                  TO_DATE(' 2020-01-01 00:00
P_2020                         TBS_YEAR_2020                  TO_DATE(' 2021-01-01 00:00
P_MAXVALUE                     USERS                          MAXVALUE

7 rows selected.

SQL> alter table sales_data
  2  merge partitions P_2019_H1, P_2019_H2
  3  into partition P_2019 tablespace TBS_YEAR_2019
  4  update indexes
  5  /

Table altered.

SQL> select partition_name, tablespace_name, high_value
  2  from user_tab_partitions
  3  where table_name = 'SALES_DATA'
  4  order by partition_position
  5  /

PARTITION_NAME                 TABLESPACE_NAME                HIGH_VALUE
------------------------------ ------------------------------ --------------------------
P_2016                         ARCHIVE_SALES_DATA             TO_DATE(' 2017-01-01 00:00
P_2017                         TBS_YEAR_2017                  TO_DATE(' 2018-01-01 00:00
P_2018                         TBS_YEAR_2018                  TO_DATE(' 2019-01-01 00:00
P_2019                         TBS_YEAR_2019                  TO_DATE(' 2020-01-01 00:00
P_2020                         TBS_YEAR_2020                  TO_DATE(' 2021-01-01 00:00
P_MAXVALUE                     USERS                          MAXVALUE

6 rows selected.

SQL> 

So, when running Table Partition DDL, be careful about the intended and actual target Tablespace(s).  (What about Index Partitions ?  The UPDATE INDEXES clause can specify target tablespaces for each Index Partition of each Index as well ... something like : (this is from the documentation on the ALTER TABLE command)

UPDATE INDEXES (cost_ix (PARTITION c_p1 tablespace tbs_02, 
                           PARTITION c_p2 tablespace tbs_03))

Partitioning -- 13b : Splitting a Partition

Let's say the business anticipates growing sales volume in 2019 and new reporting requirements.  IT analyses the requirements and decides that the SALES_DATA Table that is currently Partitioned by YEAR, needs to be Partitioned by HALF-YEAR from 2019 onwards.

SQL> select partition_name, tablespace_name
  2  from user_tab_partitions
  3  where table_name = 'SALES_DATA'
  4  order by partition_position
  5  /

PARTITION_NAME                 TABLESPACE_NAME
------------------------------ ------------------------------
P_2016                         ARCHIVE_SALES_DATA
P_2017                         TBS_YEAR_2017
P_2018                         TBS_YEAR_2018
P_2019                         TBS_YEAR_2019
P_2020                         TBS_YEAR_2020
P_MAXVALUE                     USERS

6 rows selected.

SQL> 
SQL> alter table sales_data
  2  split partition P_2019 at (to_date('01-JUL-2019','DD-MON-YYYY'))
  3  into (partition P_2019_H1, partition P_2019_H2)
  4  update indexes
  5  /

Table altered.

SQL> 
SQL> col high_value format a26 trunc
SQL> select partition_name, tablespace_name, high_value
  2  from user_tab_partitions
  3  where table_name  = 'SALES_DATA'
  4  order by partition_position
  5  /

PARTITION_NAME                 TABLESPACE_NAME                HIGH_VALUE
------------------------------ ------------------------------ --------------------------
P_2016                         ARCHIVE_SALES_DATA             TO_DATE(' 2017-01-01 00:00
P_2017                         TBS_YEAR_2017                  TO_DATE(' 2018-01-01 00:00
P_2018                         TBS_YEAR_2018                  TO_DATE(' 2019-01-01 00:00
P_2019_H1                      TBS_YEAR_2019                  TO_DATE(' 2019-07-01 00:00
P_2019_H2                      TBS_YEAR_2019                  TO_DATE(' 2020-01-01 00:00
P_2020                         TBS_YEAR_2020                  TO_DATE(' 2021-01-01 00:00
P_MAXVALUE                     USERS                          MAXVALUE

7 rows selected.

SQL> 

I used the UPDATE INDEXES clause to ensure that all (specifically Global) Indexes affected by the SPLIT are updated so that they don't go into an UNUSABLE state.

I could have optionally used a TABLESPACE clause for each of the two new Partitions P_2019_H1 and P_2019_H2


(Also see a previous BlogPost on using SPLIT PARTITION to add a new Partition at the "end" of the table by splitting the last Partition)