In a recent project, a customer used Advanced Queueing (AQ), and I had to move a single queue from one database to another.

In Oracle AI Database, you can use Data Pump to move queues. According to the documentation, exporting and importing a queue is straightforward, but there are some caveats to be aware of.

How to Export a Queue

I want to export the ORDER_Q queue in the APPUSER schema.

Under the hood, a queue consists of a queue table. Often, the queue uses an object type for its payload. I start by finding the queue table name and payload type:

select q.queue_table, qt.object_type
from   dba_queues q, dba_queue_tables qt 
where  q.owner='APPUSER' and q.name='ORDER_Q'
and    q.owner=qt.owner and q.queue_table =qt.queue_table;

   QUEUE_TABLE        OBJECT_TYPE
______________ __________________
ORDER_QT       APPUSER.ORDER_T

I prepare a Data Pump parfile named queue_table_export.par. It exports the queue table:
```
directory=dpdir
dumpfile=order_qt.dmp
logfile=order_q_export.log
tables=APPUSER.ORDER_QT
exclude=statistics
```
- The tables parameter is the queue table for the queue I want to export. I find it using the query above.

Then, I export the queue table:

expdp ... parfile=queue_table_export.par

Next, I create a new parfile named payload_type_export.par. It exports the object_type or payload_type:
```
directory=dpdir
dumpfile=queue_types.dmp
logfile=queue_types_export.log
schemas=appuser
include=type:"IN ('ORDER_T')"
```
- To export types, I must perform a schema export.
- I use the include parameter to include only types and further limit the export to the ORDER_T type.

Then, I export the type:

expdp ... parfile=payload_type_export.par

How to Import

I start by importing the type:
```
impdp ... dumpfile=queue_types.dmp
```
Then, I import the queue table:
```
impdp ... dumpfile=order_qt.dmp
```
- Data Pump imports the queue table and all messages.
- It also calls the AQ API to create the queue infrastructure.
I connect to the database and start the queue:
```
BEGIN
DBMS_AQADM.START_QUEUE(
	queue_name => 'APPUSER.ORDER_Q'
);
END;
/
```
- Note that I start the queue by its name ORDER_Q. It was created automatically during the import of the queue table.
That’s it. I’ve moved the queue and can start using it.

What Happens During Import

Let’s see how Data Pump uses the AQ API when it imports the queue table.

I start Data Pump to extract the DDL from the dump file:
```
impdp ... dumpfile=order_qt.dmp sqlfile=order_qt.sql
```
- Data Pump reads the dump file and extracts the statements needed to perform this import.
- It doesn’t perform the import.
- The statements are written to the text file specified by sqlfile.

I examine the text file. This is what Data Pump would do during an import.

Data Pump starts by creating the queue table:

CREATE TABLE "APPUSER"."ORDER_QT"
   (    "Q_NAME" VARCHAR2(128 BYTE),
        "MSGID" RAW(16),
        "CORRID" VARCHAR2(128 BYTE),
        "PRIORITY" NUMBER,
        ...

Next come a few indexes:

CREATE INDEX "APPUSER"."AQ$_ORDER_QT_I"
   ON "APPUSER"."ORDER_QT" ("Q_NAME", "STATE", "ENQ_TIME", "STEP_NO", "CHAIN_NO", "LOCAL_ORDER_NO")
   ...

Finally, the call to the AQ API to create the queue:

BEGIN
SYS.DBMS_AQ_IMP_INTERNAL.IMPORT_QUEUE_TABLE('ORDER_QT',1,16801800,2,0,0,'', SYS.DBMS_AQ_IMP_INTERNAL.DBVER_10i, '00:00');
COMMIT;
END;
/

BEGIN
SYS.DBMS_AQ_IMP_INTERNAL.IMPORT_QUEUE(HEXTORAW('598D4E9609226B60E0635301000A0A08'),'ORDER_QT','AQ$_ORDER_QT_E',1,0,0,0,0,'exception queue');
COMMIT;
END;
/

BEGIN
SYS.DBMS_AQ_IMP_INTERNAL.IMPORT_QUEUE(HEXTORAW('598D4E9609236B60E0635301000A0A08'),'ORDER_QT','ORDER_Q',0,5,0,0,0,'');
COMMIT;
END;
/

You can’t see the rows being loaded into the queue, but that happens too. All messages in the queue are also exported.

The DBMS_AQ_IMP_INTERNAL is an internal API. Don’t call it yourself.

What About a Full or Schema Export

If you perform a full or schema mode export, it’s simple. Data Pump exports all the required objects, including the types.

The only thing you must do is to start the queues after the import.

What If

The payload type must exist when you import the queue table. If you try to import the queue table without the type, Data Pump throws an error:

Processing object type TABLE_EXPORT/TABLE/TABLE
ORA-39117: Type needed to create table is not included in this operation. Failing sql is:
CREATE TABLE "APPUSER"."ORDER_QT" ("Q_NAME" VARCHAR2(128 BYTE), "MSGID" RAW(16), "CORRID" VARCHAR2(128 BYTE), "PRIORITY" NUMBER, "STATE" NUMBER, "DELAY" TIMESTAMP (6), "EXPIRATION" NUMBER, "TIME_MANAGER_INFO" TIMESTAMP (6), "LOCAL_ORDER_NO" NUMBER, "CHAIN_NO" NUMBER, "CSCN" NUMBER, "DSCN" NUMBER, "ENQ_TIME" TIMESTAMP (6), "ENQ_UID" VARCHAR2(128 BYTE), "ENQ_TID" VARCHAR2(30 BYTE), "DEQ_TIME" TIMESTAMP (6), "DEQ_UID" VARCHAR2(128 BYTE), "DEQ_TID" VARCHAR2(30 BYTE), "RETRY_COUNT" NUMBER, "EXCEPTION_QSCHEMA" VARCHAR2(128 BYTE), "EXCEPTION_QUEUE" VARCHAR2(128 BYTE), "STEP_NO" NUMBER, "RECIPIENT_KEY" NUMBER, "DEQUEUE_MSGID" RAW(16), "SENDER_NAME" VARCHAR2(128 BYTE), "SENDER_ADDRESS" VARCHAR2(1024 BYTE), "SENDER_PROTOCOL" NUMBER, "USER_DATA" "APPUSER"."ORDER_T" , "USER_PROP" "SYS"."ANYDATA" ) USAGE QUEUE SEGMENT CREATION IMMEDIATE PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255  NOCOMPRESS LOGGING STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT) TABLESPACE "USERS"  OPAQUE TYPE ("USER_PROP") STORE AS SECUREFILE LOB (ENABLE STORAGE IN ROW CHUNK 8192 CACHE  NOCOMPRESS  KEEP_DUPLICATES  STORAGE(INITIAL 106496 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645 PCTINCREASE 0 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT))

That’s It

You can use Data Pump to move queues around. For table-mode exports, remember to export the payload type separately.

A few interesting links:

Happy queueing!

Tag: queue

How to Export/Import A Single Queue Using Data Pump