DB file sequential read and read of the direct path

Similar Questions

• DB file sequential reads on the table scan complete and LRU (new)

  I would like to add a question on the subject

  scan of full table and LRU

  According to MOS doc ument 1457693.1

  «.. signs diluvium readings of the caching blocks can be divided into a number of small multiblock and self-contained bed. »

  The question is if sequential readings of db file submitted by a FULL SCAN operation will be cached on LRU or MRU list?

  I'm afraid the flushes of heat/floods the buffer cache with a lot of FULL SCAN db file sequential reads.

  For which direct path series reason readings will be inapplicable, so using this new feature of 11g is out of scope for this question.

  Thank you for your interest,

  Rainer Stenzel

  There are a few different patterns of behavior depends on the size of the table (relative to the size of the buffer cache), but the key question is probably "readings will increment the counter of touch" - because if they are not the blocks will fall the LRU list fairly quickly, if they do then the blocks could (after a few tablescans) eventually be promoted in half hot from the cache.

  I did some quick tests (that requires a little care in the Installer) which suggest the number touch was not incremented has therefore not had any effect on the question of if the block would get preferential treatment when they have reached the end of the LRU.

  I'm a little puzzled by your expression: "cached on LRU or MRU list" - it's not two different lists; but people talk about "the end of the MRU of the LRU list.

  Concerning

  Jonathan Lewis

• "the db file sequential read" waiting for event slow down an application.

  "the db file sequential read" waiting for event slow down an application.
  
  It is a rather strange problem. There is an update statement that hangs on the wait event 'db file sequential read' and until you restart the database, the query works fine. It happens once a week, usually Monday or after several days of large amount of work.
  
  I checked the processor and is fine, memory is very good, although the SGA and PGA have taken maximum memory. Flow of the disc seems to be ok since each another session on the basis of data looks very good.
  
  I guess that there is a missing configuration to avoid having to restart the database each week.
  
  Any help is greatly appreciated.

  Hello

  If you want same order of the tables as plain exp after reboot just go with ordered hint

  UPDATE item_work_step
  SET user_name = :b1,
  terminal = SYS_CONTEXT ('USERENV', 'TERMINAL'),
  status_cd = 'IN PROCESS'
  WHERE item_work_step_route_id =
  (SELECT item_work_step_route_id
  FROM (SELECT /*+ORDERED */ iws.item_work_step_route_id
  FROM user_role ur,
  work_step_role wsr,
  work_step ws,
  app_step aps,
  item_work_step iws,
  item_work iw,
  item i
  WHERE wsr.role_cd = ur.role_cd
  AND ws.work_step_id = wsr.work_step_id
  AND aps.step_cd = ws.step_cd
  AND iws.work_step_id = ws.work_step_id
  AND iws.work_id = ws.work_id
  AND iws.step_cd = ws.step_cd
  AND iws.status_cd = 'READY'
  AND iw.item_work_id = iws.item_work_id
  AND iw.item_id = iws.item_id
  AND iw.work_id = iws.work_id
  AND i.item_id = iws.item_id
  AND i.item_id = iw.item_id
  AND i.deleted = 'N'
  AND i.item_type_master_cd = :b3
  AND ur.user_name = :b1
  AND aps.app_name = :b2
  AND ( iws.assignment_user_or_role IS NULL
  OR ( iws.assignment_user_or_role IN (
  SELECT ur.role_cd
  FROM user_role ur
  WHERE ur.user_name = :b1
  UNION ALL
  SELECT :b1
  FROM dual)
  AND iws.assignment_expiration_time > SYSDATE
  )
  OR ( iws.assignment_user_or_role IS NOT NULL
  AND iws.assignment_expiration_time <= SYSDATE
  )
  )
  AND (iws.pend_date IS NULL OR iws.pend_date <= SYSDATE
  )
  ORDER BY aps.priority,
  LEAST (NVL (iw.priority, 9999),
  NVL ((SELECT NVL (priority, 9999)
  FROM item_work
  WHERE item_id = i.parent_id
  AND work_id = 42),
  9999
  )
  ),
  DECODE (i.a3, NULL, 0, 1),
  NVL (iw.sla_deadline,
  (SELECT sla_deadline
  FROM item_work
  WHERE item_id = i.parent_id
  AND work_id = 42)
  ),
  i.parent_id,
  i.item_id) unclaimed_item_work_step
  WHERE ROWNUM <= 1)
  

  If you want to get rid of the nested loops use USE_HASH

  UPDATE item_work_step
  SET user_name = :b1,
  terminal = SYS_CONTEXT ('USERENV', 'TERMINAL'),
  status_cd = 'IN PROCESS'
  WHERE item_work_step_route_id =
  (SELECT item_work_step_route_id
  FROM (SELECT /*+ORDERED USE_HASH(ur wsr ws aps iws iw i) */ iws.item_work_step_route_id
  FROM user_role ur,
  work_step_role wsr,
  work_step ws,
  app_step aps,
  item_work_step iws,
  item_work iw,
  item i
  WHERE wsr.role_cd = ur.role_cd
  AND ws.work_step_id = wsr.work_step_id
  AND aps.step_cd = ws.step_cd
  AND iws.work_step_id = ws.work_step_id
  AND iws.work_id = ws.work_id
  AND iws.step_cd = ws.step_cd
  AND iws.status_cd = 'READY'
  AND iw.item_work_id = iws.item_work_id
  AND iw.item_id = iws.item_id
  AND iw.work_id = iws.work_id
  AND i.item_id = iws.item_id
  AND i.item_id = iw.item_id
  AND i.deleted = 'N'
  AND i.item_type_master_cd = :b3
  AND ur.user_name = :b1
  AND aps.app_name = :b2
  AND ( iws.assignment_user_or_role IS NULL
  OR ( iws.assignment_user_or_role IN (
  SELECT ur.role_cd
  FROM user_role ur
  WHERE ur.user_name = :b1
  UNION ALL
  SELECT :b1
  FROM dual)
  AND iws.assignment_expiration_time > SYSDATE
  )
  OR ( iws.assignment_user_or_role IS NOT NULL
  AND iws.assignment_expiration_time <= SYSDATE
  )
  )
  AND (iws.pend_date IS NULL OR iws.pend_date <= SYSDATE
  )
  ORDER BY aps.priority,
  LEAST (NVL (iw.priority, 9999),
  NVL ((SELECT NVL (priority, 9999)
  FROM item_work
  WHERE item_id = i.parent_id
  AND work_id = 42),
  9999
  )
  ),
  DECODE (i.a3, NULL, 0, 1),
  NVL (iw.sla_deadline,
  (SELECT sla_deadline
  FROM item_work
  WHERE item_id = i.parent_id
  AND work_id = 42)
  ),
  i.parent_id,
  i.item_id) unclaimed_item_work_step
  WHERE ROWNUM <= 1)
  

  and for small tables, you can try adding for example FULL (your) FULL (wsr)

  It can be rewritten in a different way, but it's the fastest way to try how query will be if you rewrite it. Check the explain plan command if certain partially ordered tables are not joined because you can get the Cartesian join, it seems that it will be ok.

  View query result in the em console.

  Concerning

• Reason for 'control file sequential read' wait?

  Hello
  
  We have a 10.2.0.4.0 2. node RAC database on Windows 2003 (all 64-bit).
  
  By looking at the 'top 5 timed events' section AWR reports (for 1 hour), we still see the 'time of CPU", as the number one event (due to our application, certain questions if all goes well in the study now by developers...), but recently I see"sequential read from the command file"as the event number two, with 3 574 633 expects and 831 time s. I was hoping to find out what was causing this high number of expectations. I started by trying to find a particular query that has experienced this expectation often, so I ran this SQL:
  

  select sql_id, count(*)
  from dba_hist_active_sess_history
  where event_id = (select event_id from v$event_name where name = 'control file sequential read')
  group by sql_id
  order by 2 desc ;

  As I hoped, the sql_id top of page returned really stands out, with an equal number of 14 182 (the next sql_id has a counter of 68). This is the text of the sql for this id:
  

  WITH unit AS( 
            SELECT UNIQUE S.unit_id
            FROM STOCK S, HOLDER H
            WHERE  H.H_ID = S.H_ID 
              AND  H.LOC_ID  = :B2 
              AND  S.PROD_ID   = :B1 
              ) 
  SELECT  DECODE((SELECT COUNT(*) FROM unit), 1, unit_ID, NULL) 
   FROM   unit
  WHERE   ROWNUM = 1
  ;

  (Ok, code a little strange, but I already have them change it.)
  
  My question is:
  
  Why / what is this code should read in the control file?
  
  
  Kind regards
  
  ADOS
  
  PS - I also checked the block number in dba_hist_active_sess_history for this sql_id and event_id p2, and it is still one of the 5 blocks in the controlfile. I've spilled the controlfile, but do not see anything interesting (even if it is true, it is the first time I've thrown a controlfile so have no idea really what to do!).

  Hello

  ADO wrote:

  WITH unit AS(
            SELECT UNIQUE S.unit_id
            FROM STOCK S, HOLDER H
            WHERE  H.H_ID = S.H_ID
              AND  H.LOC_ID  = :B2
              AND  S.PROD_ID   = :B1
  )
  SELECT  DECODE((SELECT COUNT(*) FROM unit), 1, unit_ID, NULL)
  FROM   unit
  WHERE   ROWNUM = 1
  ;
  

  This query contains a subquery factoring clause; and as it refers to the unit twice in the main part, chances are subquery factoring is to be materialized in a global temporary table in the schema SYS with SYS_TEMP_ Name% and is accessible on two occasions in the execution plan later (check presence stage of TRANSFORMATION TABLE TEMP). The step of filling of this intermediate table requires you to write in the temporary tablespace - and it's done via direct writing. Each direct entry to the segment (i.e. directly in the file on the disk) requires a data file status check - what is online or offline - that is done by access control files. So you see these expectations. This is one of the many things why subquery factoring is not good for production OLTP environments.

• query on dba_free_space ends waiting for events db file sequential read

  Hi all
  
  Env: 10gr 2 on Windows NT
  
  I gave the query
  Select tablespace_name, sum (bytes) / 1024/1024 dba_free_space group by tablespace_name and her for still waiting.
  I checked the event waiting for v$ session and «db file sequential read»
  
  I put a trace on the session before launching the above query:
  

   
  
  
  
  OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS
  
  
  
  call     count       cpu    elapsed       disk      query    current        rows
  
  -----
  
  Parse        1      0.06       0.06          0          0          0           0
  
  Execute      1      0.00       0.00          0          0          0           0
  
  Fetch        0      0.00       0.00          0          0          0           0
  
  -----
  
  total        2      0.06       0.06          0          0          0           0
  
  
  
  Misses in library cache during parse: 1
  
  
  
  Elapsed times include waiting on following events:
  
    Event waited on                             Times   Max. Wait  Total Waited
  
    ----------------------------------------
  
    db file sequential read                     13677        0.16        151.34
  
    SQL*Net message to client                       1        0.00          0.00
  
    db file scattered read                        281        0.01          0.53
  
    latch: cache buffers lru chain                  2        0.00          0.00
  
  
  
  
  
  OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS
  
  
  
  call     count       cpu    elapsed       disk      query    current        rows
  
  ------
  
  Parse    13703      0.31       0.32          0          0          0           0
  
  Execute  14009      0.75       0.83          0          0          0           0
  
  Fetch    14139      0.48       0.74         26      56091          0       15496
  
  ------
  
  total    41851      1.54       1.89         26      56091          0       15496
  
  
  
  Misses in library cache during parse: 16
  
  Misses in library cache during execute: 16
  
  
  
  Elapsed times include waiting on following events:
  
    Event waited on                             Times   Max. Wait  Total Waited
  
    ----------------------------------------
  
    db file sequential read                        26        0.00          0.12
  
  
  
      1  user  SQL statements in session.
  
  14010  internal SQL statements in session.
  
  14011  SQL statements in session.

  I took the AWR report (for 1 hour) and the top 5 events are out like,
  
  

  Event                                 Waits    Time (s)   (ms)   Time Wait Class
  
  ------
  
  db file sequential read           1,134,643       7,580      7   56.8   User I/O
  
  db file scattered read              940,880       5,025      5   37.7   User I/O
  
  CPU time                                            967           7.2
  
  control file sequential read          4,987           3      1    0.0 System I/O
  
  control file parallel write           2,408           1      1    0.0 System I/O 

  The PHYRDS (from dba_hist_filestatxs) on my system01.dbf is 161,028,980 for the final nod.
  
  Could someone shed some light on what is happening here?
  
  TIA,
  JJ

  In certain circumstances, questioning the dictionary can be slow, usually due to problems with bad bad statistics-related implementation plans, trying to collect statistics using dbms_stats.gather_fixed_objects_stats (); It has worked for me before.
  You can also read Note 414256.1 poor performance for Tablespace Page in Grid Control display Console that also indicates a possible problem with the trash.

  HTH

  Enrique

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• Disabling the direct paths of ESX and VM guests

  Hi all

  Hope that this question has not been asked before. (I did a search but could not find anything specific).

  I'm looking for reassurance about a proposed change, we seek to bring to our system.

  We need to upgrade one of our Brocade switches that will cause some interruptions in service of the said switch. (We have two bucks and each ESX host has 2 x single port hba with a connection to each Brocade card)

  Literature, that I read, it seems to me that I have to force data store traffic over the other switch to allow me to remove the Brocade for its upgrade.

  -Proposed method for each data store attached to a host, I intend to disable the relevant path and force a failover to the remaining path that leads to the secondary Brocade.

  I have a few questions about this approach.

  (1) I guess that manually disabling a path should result in no time downtime or loss of connectivity failover occurs in an operational environment? (We will off hours, but it's a 24/7 environment).

  (2) Although the majority of our servers use VMFS, some use LUN RAW. These servers would encounter difficulties if I force a failover situation through a path of disabling?

  Thanks in advance!

  Hello

  Welcome to the community

  Hope that this question has not been asked before. (I did a search but could not find anything specific).

  It was asked before several times, in any case

  (1) I guess that manually disabling a path should result in no time downtime or loss of connectivity failover occurs in an operational environment? (We will off hours, but it's a 24/7 environment).

  (2) Although the majority of our servers use VMFS, some use LUN RAW. These servers would encounter difficulties if I force a failover situation through a path of disabling?

  1. OK, even if you remove a cable adapter HBA, ESX would shift all traffic to the next available path. Don't forget that you have the vmware tools installed in the virtual machine
  2. No problem with RAW LUN, it would behave like VMFS
  See you soon
  Artur
  

  Please, do not forget the points of call of the "useful" or "correct" answers

• See bug handles (and confiscation) with the direct Selection of the 5.5 tool?

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  Fact View > Show Edges help?