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SELECTING FROM EXTERNAL TABLE WITH CLOB perform very slow and High Wait On 'Px Deq Credit: Send Blkd ' (Doc ID 1300645.1)

Last updated on FEBRUARY 28, 2019

Applies to:

Oracle Database - Enterprise Edition - Version 10.2.0.4 to 11.2.0.1 [Release 10.2 to 11.2]
Information in this document applies to any platform.
***Checked for relevance on 22-AUG-2012***

Symptoms

NOTE: In the images and/or the document content below, the user information and data used represents fictitious data from the Oracle sample schema(s) or Public Documentation delivered with an Oracle database product. Any similarity to actual persons, living or dead, is purely coincidental and not intended in any manner.


-- Problem Statement:
On 10.2.0.4.0 in Production:
When attempting to create a table as CTAS from an external table,
the progress is very slow and there are high waits on 'PX DEQ CREDIT: SEND BLKD ':

-- Steps To Reproduce:
The issue can be reproduced at will with the following steps:
1. Create a table with data.

2. Create an external table like this:

CREATE TABLE test_terminals
ORGANIZATION EXTERNAL
(
TYPE ORACLE_DATAPUMP
DEFAULT DIRECTORY test
LOCATION ('proba_terms01.dmp', 'proba_terms02.dmp', 'proba_terms03.dmp', 'proba_terms04.dmp',
'proba_terms05.dmp', 'proba_terms06.dmp', 'proba_terms07.dmp', 'proba_terms08.dmp',
'proba_terms09.dmp', 'proba_terms10.dmp', 'proba_terms11.dmp', 'proba_terms12.dmp',
'proba_terms13.dmp', 'proba_terms14.dmp', 'proba_terms15.dmp', 'proba_terms16.dmp',
'proba_terms17.dmp', 'proba_terms18.dmp', 'proba_terms19.dmp', 'proba_terms20.dmp')
)
PARALLEL 20
AS SELECT i_to_id(i) as terminal_id,
msisdn_to_id(msisdn) as subscriber_id,
phonetype,
impstat,
settings,
firstconfig,
usedconfig,
lastmodif
FROM terminals t1
WHERE NOT EXISTS
(SELECT imei
FROM terminals t2
WHERE t2.imei = t1.imei
AND t1.lastmodif < t2.lastmodif);

It will take a long time. A couple of hours.

3. Try to create an internal table from the external table, like this:

CREATE TABLE terminals_tmp
PARTITION BY hash(terminal_id)
partitions 128 nocache
PARALLEL 20
AS SELECT
i_id, subscriber_id, phonetype, impstat,
settings, firstconfig, usedconfig, lastmodif
from test_terminals;

This will never finish.

Cause

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In this Document
Symptoms
Cause
Solution
References


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