Databases
StackOverflow2013
Postsdbo
POoracle 11g execution plan behaviour
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POoracle 11g execution plan behaviour
    primarykey
    data
    text
    <p>I have this very simple query performing filtering and join by rowid.</p> <pre><code>SELECT * FROM BOOKING.BOOKING_GRID BG, BOOKING.BOOKING_STATES BS WHERE BG.hotel=128 AND BS.ROWID =BG.BOOKINGSTATE; </code></pre> <p>when I explain plan I get:</p> <pre><code>PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Plan hash value: 1597031677 -------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | -------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 6137K| 1041M| | 1763K (1)| 05:48:27 | |* 1 | HASH JOIN | | 6137K| 1041M| 538M| 1763K (1)| 05:48:27 | |* 2 | INDEX UNIQUE SCAN| BOOKING_GRIDPK | 6137K| 468M| | 547K (1)| 01:48:05 | |* 3 | INDEX RANGE SCAN| BOOKING_GRID_INDEX5 | 6137K| | | 90388 (1)| 00:17:52 | | 4 | TABLE ACCESS FULL| BOOKING_STATES | 158M| 14G| | 365K (2)| 01:12:14 | -------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 1 - access("BS".ROWID="BG"."BOOKINGSTATE") 2 - access("BG"."HOTEL"=128) 3 - access("BG"."HOTEL"=128) </code></pre> <p>Index for BOOKING_GRID are:</p> <pre><code>BOOKING BOOKING_GRIDPK UNIQUE VALID IOT - TOP N NO NO HOTEL, DAY, BOOKINGSTATE BOOKING BOOKING_GRID_UNIQ UNIQUE VALID NORMAL N NO NO HOTEL, DAY, BOOKING, VALIDITYSTART BOOKING BOOKING_GRID_INDEX5 NONUNIQUE VALID NORMAL N NO NO HOTEL, BOOKINGSTATUS, ISDAYUSE, DAY BOOKING BOOKING_GRID_INDEX7 NONUNIQUE VALID NORMAL N NO NO HOTEL, BOOKING, VALIDITYSTART BOOKING BOOKING_GRID_INDEX10 NONUNIQUE VALID NORMAL N NO NO HOTEL, ISDAYUSE, BOOKINGSTATUS, DAY </code></pre> <p>Index for BOOKING_STATES are:</p> <pre><code>BOOKING BOOKING_STATES_PK UNIQUE VALID NORMAL N NO NO HOTEL, BOOKING, VALIDITYSTART BOOKING BOOKING_STATES_INDEX2 NONUNIQUE VALID NORMAL N NO NO HOTEL, YIELDROOMTYPE, BOOKEDROOMTYPE, ROOMTYPE BOOKING BOOKING_STATES_BOOKING NONUNIQUE VALID NORMAL N NO NO HOTEL, BOOKING, BOOKINGSTATUS BOOKING BOOKING_NOSEGMENT_INDEX NONUNIQUE VALID FUNCTION-BASED NORMAL N NO ENABLED NO SYS_NC00034$ TO_NUMBER(DECODE(TO_CHAR("MARKETSEGMENT"),NULL,DECODE("BOOK",0,NULL,TO_CHAR(DECODE("ISDAYUSE",'N',DECODE("ISSHARED",'N',DECODE("BOOKINGSTATUS",'B',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND"),'I',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND"),'W',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND")))))))) BOOKING BOOKING_NORATE_CODE_INDEX NONUNIQUE VALID FUNCTION-BASED NORMAL N NO ENABLED NO SYS_NC00033$ TO_NUMBER(DECODE(TO_CHAR("RATECODE"),NULL,DECODE("BOOK",0,NULL,TO_CHAR(DECODE("ISDAYUSE",'N',DECODE("ISSHARED",'N',DECODE("BOOKINGSTATUS",'B',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND"),'I',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND"),'W',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND")))))))) BOOKING BOOKING_NOBOOKINGTYPE_INDEX NONUNIQUE VALID FUNCTION-BASED NORMAL N NO ENABLED NO SYS_NC00032$ TO_NUMBER(DECODE(TO_CHAR("BOOKINGTYPE"),NULL,DECODE("BOOK",0,NULL,TO_CHAR(DECODE("ISDAYUSE",'N',DECODE("ISSHARED",'N',DECODE("BOOKINGSTATUS",'B',"HOTEL"*10000+LEAST("DEPARTURE","VALIDITYEND")))))))) BOOKING BOOKING_STATES_BOOKING_TYPE NONUNIQUE VALID NORMAL N NO NO HOTEL, BOOKINGTYPE, ISDAYUSE, BOOKINGSTATUS BOOKING BOOKING_STATES_CANCEL_INDEX NONUNIQUE VALID FUNCTION-BASED NORMAL N NO ENABLED NO SYS_NC00035$, SYS_NC00036$ DECODE("BOOKINGSTATUS",'c',"HOTEL",'C',"HOTEL") BOOKING BOOKING_STATES_CANCEL_INDEX NONUNIQUE VALID FUNCTION-BASED NORMAL N NO ENABLED NO SYS_NC00035$, SYS_NC00036$ DECODE("BOOKINGSTATUS",'c',"CANCELREASON",'C',"CANCELREASON") </code></pre> <p>I don't understand two things:</p> <ol> <li>why Oracle would decide it is faster to join before filtering on hotel=128?</li> <li>why using a hash join when it could use a "TABLE ACCESS BY USER ROWID"</li> </ol> <p>The weird thing is that when I run the same exact request with hotel=201, it is perfectly fine:</p> <pre><code>PLAN_TABLE_OUTPUT ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Plan hash value: 4251203092 --------------------------------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | --------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 591K| 100M| 643K (1)| 02:07:12 | | 1 | NESTED LOOPS | | 591K| 100M| 643K (1)| 02:07:12 | |* 2 | INDEX UNIQUE SCAN | BOOKING_GRIDPK | 591K| 45M| 52686 (1)| 00:10:25 | |* 3 | INDEX RANGE SCAN | BOOKING_GRID_INDEX5 | 591K| | 8707 (1)| 00:01:44 | | 4 | TABLE ACCESS BY USER ROWID| BOOKING_STATES | 1 | 98 | 1 (0)| 00:00:01 | --------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("BG"."HOTEL"=201) 3 - access("BG"."HOTEL"=201) </code></pre> <p>Any idea about what's going on there?</p> <p>Thank you,</p> <p>Renaud</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USRenaudBlue
    1. USRenaudBlue
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POoracle 11g execution plan behaviour
      1. This table or related slice is empty.
      1. VTUpMod
    1. COOf course any peace of advice about how to investigate by myself are welcome :). I tried to dig into V$SQL_PLAN but I didn't really get how to grab information from it.
      singulars
      1. POoracle 11g execution plan behaviour
      1. USRenaudBlue
    2. COWhat does BG.BOOKINGSTATE represent? Why is it being compared to ROWID?
      singulars
      1. POoracle 11g execution plan behaviour
      1. USOldProgrammer
    3. COYes, Oracle provides a way to store physical rowid (supposed to be the fastest way to join) under the condition they can never change (this is a setting in the DB). This is what we did, BG.bookingstate is the rowid of a row in BS.
      singulars
      1. POoracle 11g execution plan behaviour
      1. USRenaudBlue
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload