Hi Lothar,
As for the MOS Note: I always read partitioned table.... where is that 16k
block bit Mikhail also mentioned?
Hi Stefan,
thanks for answering. My question is indeed why dynamic sampling even
considers empty blocks at the start of the Segment.
As for the MOS Note: I always read partitioned table.... where is that 16k
block bit Mikhail also mentioned?
Regards
Lothar
----Ursprüngliche Nachricht----
Von : contact@xxxxxxxx
Datum : 28/01/2020 - 21:48 (MZ)
An : l.flatz@xxxxxxxxxx, oracle-l@xxxxxxxxxxxxx
Betreff : Re: segment covers more blocks than needed
Hello Lothar,
Mikhail is referring to the behavior that is described in MOS ID
#1295484.1.
However I am not quite sure what your question is. You said that you are
using an uniform extent size - what size is it? Might it be round about 8
MB - this would explain the behavior for non-partitioned tables as well.
Jonathan already explained the FTS behavior with the LHWM / HHWM.
So maybe only one point left: Why does dynamic sampling screw it up?
Do you see something like "DS Failed for ..." in the CBO trace file? AFAIK
there is a sanity check - the DS result can be ignored if number of sampled
blocks is small and the "filtered sample card." is zero ... or maybe some
DS bugs as usual ;-)
Best Regards
Stefan Koehler
Independent Oracle performance consultant and researcher
Website: http://www.soocs.de
Twitter: @OracleSK
Lothar Flatz <l.flatz@xxxxxxxxxx> hat am 28. Januar 2020 um 21:02geschrieben:
course not partitioned.
Hi ,
thanks, I will check the hidden param tomorrow. The tables are of
But the 16k tablespace is correct. Can you point me to your source?would be good for DWH.
Funny what consquences that illfounded statment had that blocksize >8k
on behalf of l.flatz@xxxxxxxxxx < l.flatz@xxxxxxxxxx>
Regards
Lothar
From: oracle-l-bounce@xxxxxxxxxxxxx < oracle-l-bounce@xxxxxxxxxxxxx>
used.Sent: 28 January 2020 15:50
To: Oracle-L@xxxxxxxxxxxxx
Subject: segment covers more blocks than needed
Hi,
I am no classical DBA, thus this question might be trivia for youl.
This issue causes serious misestomate when dynamic_sampling >= 4 is
blocks in DBA_TABLES.We got a DWH with many small tables where stats are showing 502
querying dba_tables of course.Empty blocks is 0.
The Point is that there must be blocks which must (almost?) empty.
502 Blocks Matches with the initial size of the Segment.
We did a testcase. We created am empty table. No blocks when
, again 502 appeared in dba_tables.After we inserted the first row (deferred_segment_creation = true)
set after the first block.DBMS_SPACE features this Output:
L/SQL-Prozedur erfolgreich abgeschlossen.
Unformatted Blocks = 486
Unformatted Bytes = 7962624
FS1 Bytes (at least 0 to 25% free space) = 0
FS1 Blocks(at least 0 to 25% free space) = 0
FS2 Bytes (at least 25 to 50% free space)= 0
FS2 Blocks(at least 25 to 50% free space)= 0
FS3 Bytes (at least 50 to 75% free space) = 0
FS3 Blocks(at least 50 to 75% free space) = 0
FS4 Bytes (at least 75 to 100% free space) = 262144
FS4 Blocks(at least 75 to 100% free space)= 16
Full Blocks in segment = 0
Full Bytes in segment = 0
Segment_space_managment is AUTO. Tablespace has a uniform extent.
Runtime Stats show 28 buffers on FTS, proving that the HWM is not
--Avg_row_len is 200. Remember this is only 1 row.
What is going on here?
Regards
Lothar
//www.freelists.org/webpage/oracle-l
--
//www.freelists.org/webpage/oracle-l