External Table Access Slow After Upgrade From 10g To 11g (Doc ID 1985242.1)

Last updated on NOVEMBER 02, 2016

Applies to:

Oracle Database - Enterprise Edition - Version 11.2.0.4 to 12.1.0.2 [Release 11.2 to 12.1]
Information in this document applies to any platform.
***Checked for relevance on 02-Nov-2016***

Symptoms

After upgrading from 10g to 11g access to external tables is very slow.

A query against an external table that completes in 37 second takes 10 minutes in 11g.

10046 Trace shows that the following recursive statement is the cause of the slowness with wait event 'external table open' :

SELECT DBTIMEZONE, LENGTH(DBTIMEZONE) FROM SYS.DUAL

WAIT #4573367968: nam='external table open' ela= 46 filectx=4574619472 file#=0 p3=0 obj#=-1 tim=72965428056588
WAIT #4573367968: nam='external table read' ela= 2494 filectx=4574619472 file#=12 size=524288 obj#=-1 tim=72965428059103
WAIT #4573367968: nam='external table read' ela= 6848 filectx=4574619472 file#=12 size=524288 obj#=-1 tim=72965428126407

.......

From Tkprof The main select statement on the external table is the significant waited one , and dose not show the previous statement :

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.01          0        543          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1    365.92     601.68          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3    365.93     601.69          0        543          0           0

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 84  
Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max)  Row Source Operation
---------- ---------- ----------  ---------------------------------------------------
        0          0          0  EXTERNAL TABLE ACCESS FULL GE150I01_HDR (cr=38 pr=0 pw=0 time=601710353 us cost=29 size=2448 card=408)

 

Changes

upgrading from 10g to 11g

Cause

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