Problem debugging for DBFS

In trying to find out the cause of a DBFS issue, I learned what is expected (or helpful) when working with Support on DBFS issues.

1)  Logon trigger for dbfs user to create a trace file..

CREATE OR REPLACE TRIGGER DBFS_LOGON
AFTER LOGON
ON DATABASE
declare
username VARCHAR2(30);
BEGIN
  username:=SYS_CONTEXT('USERENV','SESSION_USER');
  IF username like 'FOO' then
    dbms_dbfs_content.setTrace(3);
    execute immediate 'alter session set events ''45050 trace name context forever, level 0xfffff'' ';
  END IF;
EXCEPTION
   WHEN OTHERS THEN
      NULL;
END;
/ 

2) Start the DBFS client with tracing turned on.  (-otrace_file=,trace_level=2,trace_size=0). (see How to trace DBFS when any failure happens [ID 1320683.1])

Remember if you are running DBFS, you are probably on a multi-node clustered environment, so you only need to do these steps on one of the nodes to gather the data.  I turned the logon trigger on, remounted the FS with tracing..  reproduced issue. Verified the log files were created, disabled trigger, remounted without tracing..  I did this on only one node, and gathered what I needed with minimal issues.

Where is my space on DBFS

I just ran into an issue on DBFS where I ran out of space.

First here is the df -k

Filesystem           1K-blocks      Used Available Use% Mounted on
dbfs-dbfs_admin2@:/   20983808  11443696   9540112  55% /dbfs/dba

OK, everything looks good.. I am using 11g and I have 9.5g available.

I go to copy a file on the os (you can see it is 240m).  Lots of room

 ls -al bsg.out
-rw-r--r-- 1 oracle oinstall 240794862 May 18 11:37 bsg.out

cp bsg.out bsg.out1
cp: writing `bsg.out1': No space left on device
cp: closing `bsg.out1': No space left on device

So where is my space.  ?? I find this query..

set serveroutput on;
declare
v_segment_size_blocks number;
v_segment_size_bytes number;
v_ number;
v_used_blocks number;
v_used_bytes number;
v_expired_blocks number;
v_expired_bytes number;
v_unexpired_blocks number;
v_unexpired_bytes number;
begin
dbms_space.space_usage ('DBFS_OWNER', 'LOB_SFS$_FST_12345', 'LOB', 
v_segment_size_blocks, v_segment_size_bytes,
v_used_blocks, v_used_bytes, v_expired_blocks, v_expired_bytes, 
v_unexpired_blocks, v_unexpired_bytes );
dbms_output.put_line('Segment Size blocks = '||v_segment_size_blocks);
dbms_output.put_line('Segment Size bytes = '||v_segment_size_bytes);
dbms_output.put_line('Used blocks = '||v_used_blocks);
dbms_output.put_line('Used bytes = '||v_used_bytes);
dbms_output.put_line('Expired Blocks = '||v_expired_blocks);
dbms_output.put_line('Expired Bytes = '||v_expired_bytes);
dbms_output.put_line('UNExpired Blocks = '||v_unexpired_blocks);
dbms_output.put_line('UNExpired Bytes = '||v_unexpired_bytes);
end;
/

And I see this output

Segment Size blocks = 2619024
Segment Size bytes = 21455044608
Used blocks = 1425916
Used bytes = 11681103872
Expired Blocks = 1190111
Expired Bytes = 9749389312
UNExpired Blocks = 0
UNExpired Bytes = 0

So.. according to this.. The segment is 21.4 g

11.7g is used space
  9.7g is Expired space
   0g   is unexpired space.

So if I have 9.7g of Expired space why can't I use it ??  My file is only 244m, and I should have 9.7 g available.

So my questions out of this are (if anyone knows the answer).

1) How does this happen and how do I avoid it ?

2) How do I size tablespaces for DBFS ?  They need more space to be available then I need for the file system.

3) How do I monitor the sizing since the DF -k does not report unexpired bytes that are available to be used ?

4) How does the clause "retention" fit into this ?  retention defaults to "auto" rather than "none".  Can I set it to "none", but what happens and does this solve my problem ?


Oh, and I wanted to make sure that I included the ouput of  whats in the tablespace.

SEGMENT_NAME                                             SEGMENT_TYPE       SEGMENT_SIZE
-------------------------------------------------------- ------------------ ------------
LOB_SFS$_FST_12345                                       LOBSEGMENT                20461
T_ADMIN                                                  TABLE                        17
IP_SFS$_FST_12345                                        INDEX                         4
IPG_SFS$_FST_12345                                       INDEX                         3
IG_SFS$_FST_12345                                        INDEX                         2
SYS_IL0000095835C00007$$                                 LOBINDEX                      0

UPDATE (6/13/12)  --

After working with support on this, it was filed as a bug.  This occured because I was using DBFS as a filesytem for my dbreplay capture.  After thinking about it the dbcapture is probably the most intensive workload I could throw at DBFS.  Not only does it simultaneously write to multiple files, but it writes to those files across multiple nodes.  In my capture there were 4 nodes writing to 100's of files at the same time.
   I will be testing the patch, and see if it corrects the problem.  Support is telling me that the writing across multiple nodes is causing some of the issues..

Analytical functions

I have been working on a query that is uses an analytical function..
I’m not familiar with them, but using my usual query tuning got me into some trouble..

This is the query.

WITH
SACOMMON71991 AS (select T17189.SUR_REF_TIME_PERD_ID as SUR_REF_TIME_PERD_ID,
    T17189.RTP_CAL_DT as c4,
    T17189.RTP_CAL_YR as c5,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR ORDER BY
T17189.RTP_CAL_YR DESC) as c6,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR,
T17189.SUR_REF_TIME_PERD_ID ORDER BY T17189.RTP_CAL_YR DESC,
T17189.SUR_REF_TIME_PERD_ID DESC) as c7
from
    REF_TIME_PERD T17189 /* Dim_TIME_PERD_D_Check_Date */ )
select * from SACOMMON71991 where SUR_REF_TIME_PERD_ID=20240213

The data in the table looks like this.

SUR_REF_TIME_PERD_ID    varchar(8)
RPT_CAL_DT                      date
RPT_CAL_YR                      varchar(4)

Some example values are.

SUR_REF_TIME_PERD_ID            RPT_CAL_DT              RPT_CAL_YR
19000101                                         01/01/1900                    1900
…
20120101                                         01/01/2012                    2012
-..
--
20120125                                          01/25/2012                    2012
..
20120430                                          04/30/2012                    2012
..
20240213                                          02/13/2024                    2024
..
47121231                                           12/31/4712                   4712


Now back to my query..

WITH
SACOMMON71991 AS (select T17189.SUR_REF_TIME_PERD_ID as SUR_REF_TIME_PERD_ID,
    T17189.RTP_CAL_DT as c4,
    T17189.RTP_CAL_YR as c5,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR ORDER BY T17189.RTP_CAL_YR DESC) as c6,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR,T17189.SUR_REF_TIME_PERD_ID ORDER BY T17189.RTP_CAL_YR DESC,T17189.SUR_REF_TIME_PERD_ID DESC) as c7
from
    REF_TIME_PERD T17189 /* Dim_TIME_PERD_D_Check_Date */ )
select * from SACOMMON71991 where SUR_REF_TIME_PERD_ID=20240213

I noticed that the query did a full table scan of 219,000 rows.

  I figured, well I only wanted 1 row, so why can’t I just change the
query ??

select T17189.SUR_REF_TIME_PERD_ID as SUR_REF_TIME_PERD_ID,
     T17189.RTP_CAL_DT as c4,
     T17189.RTP_CAL_YR as c5,
     ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR ORDER BY T17189.RTP_CAL_YR DESC) as c6,
     ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR, T17189.SUR_REF_TIME_PERD_ID ORDER BY T17189.RTP_CAL_YR DESC, T17189.SUR_REF_TIME_PERD_ID DESC) as c7
from 
     V_REF_TIME_PERD T17189  where SUR_REF_TIME_PERD_ID=20240213

My plan looks much better

But the answer is different ??

The first query returns.

SUR_REF_TIME_PERD_ID C4                            C5         C6         C7
-------------------- --------------------- ---------- ---------- ----------
            20240213 2024-02-13 00:00:00         2024         44          1

The second query returns

SUR_REF_TIME_PERD_ID C4                            C5         C6         C7
-------------------- --------------------- ---------- ---------- ----------
            20240213 2024-02-13 00:00:00         2024          1          1

So what exactly is the query doing ???

The query is actually analyzing more data than just my row.  After examining the query, I noticed the 4th column (C6) is actually the day of the year.  2/13 is the 44th day of the year.

So what exactly is the query doing to get this ???

It is starting with all rows in the table, then sorting them by RPT_CAL_YR, and SUR_REF_TIME_PERD_ID.  This is column c7 in table.. If we look back we see this column is

ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR, T17189.SUR_REF_TIME_PERD_ID ORDER BY T17189.RTP_CAL_YR DESC, T17189.SUR_REF_TIME_PERD_ID DESC) as c7

This column does the sorting to get the result.. Now if you look at C6, you see that it is a row_number over just the 1 column RPT_CAL_YR.  Since the rows are now sorted in data order (thanks to c7), C6 is just  the row number for the value passed to the query..

I know it gets kind of complicated.. The lesson learned from this, is that analytical functions sometimes need to do FTS to do their work.  By giving it the key value within the select, I removed the queries ability to look at the full tables data.

I also learned that by properly limiting the values in the right spot, you can eliminate rows.  Here is a better query. I am limiting the analytical function to just look at the current year.

   WITH
SACOMMON71991 AS (select T17189.SUR_REF_TIME_PERD_ID as SUR_REF_TIME_PERD_ID,
    T17189.RTP_CAL_DT as c4,
    T17189.RTP_CAL_YR as c5,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR ORDER BY
T17189.RTP_CAL_YR DESC) as c6,
    ROW_NUMBER() OVER (PARTITION BY T17189.RTP_CAL_YR,
T17189.SUR_REF_TIME_PERD_ID ORDER BY T17189.RTP_CAL_YR DESC,
T17189.SUR_REF_TIME_PERD_ID DESC) as c7
from
    REF_TIME_PERD T17189 /* Dim_TIME_PERD_D_Check_Date */ 
    where RTP_CAL_YR='2024')
select * from SACOMMON71991 where SUR_REF_TIME_PERD_ID=20240213

The plan is going through less data, but the appropriate data to get the right answer.

Hyperthreading with Oracle (update)

After my first post on hyperthreading, and all the hits I've been getting I've decided to update it..

My first post was pased on testing with a DL980.. This is an 8 socket server with   X7560  @ 2.27GHz processes.

My currently updated post is on a new 2 socket server with the E7- 2870 @ 2.40GHz chipset.

The servers I tested on were

2 Socket
10 Core (dual threaded)
11.2.0.3 Oracle
Linux RHEL  2.6.18-274.17.1.el5
132g of ram.


I tested by using Kevin Clossons SLOB test which can be found here.

I tested using multiple process settings, and you see how these  servers scaled up with the processes.

I warmed up with 15 processes.  Looking at the LIO count, we are doing 7.2 million. output

Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               14.4               24.9       0.00       4.60
       DB CPU(s):               14.3               24.7       0.00       4.56
       Redo size:           13,974.5           24,137.1
   Logical reads:        7,259,470.5       12,538,708.3
   Block changes:               32.9               56.8
  Physical reads:               69.9              120.8
 Physical writes:               15.8               27.2
      User calls:                3.1                5.4
          Parses:                3.8                6.6
     Hard parses:                0.0                0.0
W/A MB processed:                0.4                0.7
          Logons:                0.1                0.2
        Executes:           28,206.8           48,719.3
       Rollbacks:                0.0                0.0
    Transactions:                0.6

Then 20 processes.  8.7 million still looking good.  output

Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               18.9              127.0       0.00      10.83
       DB CPU(s):               18.9              126.8       0.00      10.82
       Redo size:           15,073.6          101,207.6
   Logical reads:        8,714,693.4       58,512,431.8
   Block changes:               39.2              263.4
  Physical reads:                2.1               13.9
 Physical writes:               13.0               87.0
      User calls:                1.8               11.7
          Parses:                3.8               25.6
     Hard parses:                0.0                0.1
W/A MB processed:                0.4                2.5
          Logons:                0.1                0.4
        Executes:           33,859.7          227,341.5
       Rollbacks:                0.0                0.0
    Transactions:                0.2

Now lets try 25.. see how we go past the number of cores .  9.4 million.. Hyperthreading is scaling nicely. output

Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               23.1               91.7       0.00       9.26
       DB CPU(s):               23.0               91.6       0.00       9.24
       Redo size:           21,634.2           86,063.7
   Logical reads:        9,406,658.2       37,420,998.8
   Block changes:               68.2              271.4
  Physical reads:                3.7               14.8
 Physical writes:                5.7               22.5
      User calls:                2.5                9.9
          Parses:                3.3               13.3
     Hard parses:                0.1                0.3
W/A MB processed:                0.4                1.6
          Logons:                0.1                0.5
        Executes:           36,544.7          145,380.0
       Rollbacks:                0.0                0.0
    Transactions:                0.3

Next 35.. Still scaling... output

Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               33.5              310.9       0.00      18.74
       DB CPU(s):               33.5              310.3       0.00      18.70
       Redo size:            9,379.2           86,997.8
   Logical reads:       11,039,158.6      102,395,221.3
   Block changes:               17.7              164.4
  Physical reads:                1.3               12.0
 Physical writes:                4.0               36.9
      User calls:                1.8               16.6
          Parses:                2.0               18.9
     Hard parses:                0.1                1.0
W/A MB processed:                0.2                2.2
          Logons:                0.1                0.6
        Executes:           42,882.8          397,765.4
       Rollbacks:                0.0                0.0
    Transactions:                0.1

Finally the number of threads.  This appears to be the peak. output

Load Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               38.3              387.0       0.00      17.48
       DB CPU(s):               37.6              380.4       0.00      17.18
       Redo size:            9,207.1           93,060.2
   Logical reads:       11,577,951.1      117,023,088.1
   Block changes:               16.4              166.1
  Physical reads:                1.1               11.5
 Physical writes:                4.5               45.1
      User calls:                2.2               22.1
          Parses:                2.0               19.9
     Hard parses:                0.1                0.6
W/A MB processed:                0.2                2.5
          Logons:                0.1                0.9
        Executes:           44,975.6          454,587.0
       Rollbacks:                0.0                0.0
    Transactions:                0.1

Now lets go up to 45 ...   things start dropping off.  output

oad Profile              Per Second    Per Transaction   Per Exec   Per Call
~~~~~~~~~~~~         ---------------    --------------- ---------- ----------
      DB Time(s):               40.7              482.9       0.00      16.78
       DB CPU(s):               36.0              427.5       0.00      14.86
       Redo size:            8,205.8           97,318.2
   Logical reads:       11,100,719.6      131,651,002.6
   Block changes:               14.0              165.9
  Physical reads:                0.9               10.3
 Physical writes:                3.2               38.3
      User calls:                2.4               28.8
          Parses:                2.3               27.5
     Hard parses:                0.1                0.6
W/A MB processed:                0.3                3.6
          Logons:                0.1                1.4
        Executes:           43,122.5          511,418.6
       Rollbacks:                0.0                0.0
    Transactions:                0.1

So if you look at the throughput..

20 processes    8,7 Million LIO's
40 Processes   11.6 Million LIO's

Not quite linaear progression, but things don't really top off until I get to the number of threads..  This scaled much better, and it seems that hyperthreading is helpgin push more workload through.