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Difference between ROWID and ROWID BATCHED in Oracle
https://www.ktexperts.com/difference-between-rowid-and-rowid-batched-in-oracle/
oracle - Difference between table access by index rowid ...
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TABLE ACCESS BY INDEX ROWID BATCHED | Mohamed Houri’s
https://hourim.wordpress.com/2014/09/23/table-access-by-index-rowid-batched/
September 23, 2014 September 23, 2014 TABLE ACCESS BY INDEX ROWID BATCHED Filed under: — hourim @ 7:05 pm I was writing an article for about Indexing strategy: discard and sort and testing the model supporting this article in different oracle database releases 10gR2, 11gR2 and 12cR1 until my attention has been kept by an interesting detail in 12cR1.
Observe the following execution plans taken from 12cR1 in response to the following query: select * from t1 where id2 = 42 order by id1 desc; ------------------------------------------------------------------------ | Id | Operation | Name | Starts | E-Rows | A-Rows | ------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | | 1000 | |* 1 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 499K| 1000 | | 2 | INDEX FULL SCAN DESCENDING| T1_PK | 1 | 998K| 1000K| ------------------------------------------------------------------------ Predicate Information (identified by operation id): --------------------------------------------------- 1 - filter("ID2"=42) --------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | --------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 1000 | | 1 | TABLE ACCESS BY INDEX ROWID| T1 | 1 | 499K| 1000 | |* 2 | INDEX RANGE SCAN | T1_IND_ID1_FBI | 1 | 499K| 1000 | --------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 2 - access("ID2"=42) ------------------------------------------------------------------------------ | Id | Operation | Name | Starts | E-Rows | A-Rows | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1 | | 1000 | | 1 | TABLE ACCESS BY INDEX ROWID | T1 | 1 | 499K| 1000 | |* 2 | INDEX RANGE SCAN DESCENDING | T1_IND_ID1_NI | 1 | 499K| 1000 | ------------------------------------------------------------------------------ Predicate Information (identified by operation id): -------------------------------------------------- 2 - access("ID2"=42) Question: What have you already pointed out from the above execution plans?
Answer : I have managed to design indexes so that Oracle succeeded to avoid the order by operation for each of the above query executions (there is no order by operation in the above execution plan).
But this is not the reason which paved the way to this article. Wait a minute and will you know what motivated this article.
In my incessant desire to help the CBO doing good estimations, I created a virtual column(derived_id2), singularly indexed it with a b-tree index, collected statistics for this virtual column and executed a new but equivalent query: SQL> select * from t1 where derived_id2 = 42 order by id1 desc; Which has been honored via the following execution plan -------------------------------------------------------------------------------------------------- | Id | Operation | Name | Starts | E-Rows | A-Rows | -------------------------------------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | | 1000 | | 1 | SORT ORDER BY | | 1 | 511 | 1000 | | 2 | TABLE ACCESS BY INDEX ROWID BATCHED| T1 | 1 | 511 | 1000 | |* 3 | INDEX RANGE SCAN | T1_DERIVED_ID2_IND_BIS | 1 | 511 | 1000 | -------------------------------------------------------------------------------------------------- Predicate Information (identified by operation id): --------------------------------------------------- 3 - access("DERIVED_ID2"=42) Question : Have you already noticed something?
Answer : The appearance of a SORT ORDER BY operation above TABLE ACCESS BY INDEX ROWID
It seems that the new 12c TABLE ACCESS BY INDEX ROWID cannot take place when Oracle uses the index access child operation to avoid the order by operation. In the first three execution plans above, Oracle uses an index access path to avoid the order by operation and in these cases the parent index table has been visited via the classical table access by index rowid. While when Oracle has been unable to eliminate the order by operation, the parent index child table has been accessed via the new 12c table access by index rowid batched followed by, what seems to be inevitable in this case, an order by operation.
Here below is a simple model you can play with to check this impossible to separate couple (order by, table access by index rowid batched) create table t1 as select rownum n1 ,trunc((rownum-1)/3) n2 ,rpad('x',100) v1 from dual connect by level <= 1e4; create index t1_ind1 on t1(n2, n1); select * from t1 where n2 = 3329 order by n1 desc; select * from table(dbms_xplan.display_cursor); alter index t1_ind1 invisible; create index t1_ind2 on t1(n2); select * from t1 where n2 = 3329 order by n1 desc; select * from table(dbms_xplan.display_cursor); Share this:Like this:Like Loading... Related2 Comments » 2 Comments […] As you can see, this time, in contrast to the first two cases, a SORT ORDER BY operation kicks in. This operation becomes mandatory since the result set has been desired in an order that doesn’t match the order of the index columns. Spot in passing that when Oracle avoids a SORT ORDER BY it doesn’t visit the T1 table in a BATCHED mode and vice versa. I have already wrote a note about this here. […] Pingback by — April 29, 2017 @ | Thank you for this article. Comment by — March 24, 2020 @ | Leave a Reply Enter your comment here... Fill in your details below or click an icon to log in: Email (required) (Address never made public) Name (required) Website You are commenting using your WordPress.com account. ( / ) You are commenting using your Google account. ( / ) You are commenting using your Twitter account. ( / ) You are commenting using your Facebook account. ( / ) Connecting to %s Notify me of new comments via email. Notify me of new posts via email. Δ This site uses Akismet to reduce spam. . Search for:
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Difference between table access by index rowid BATCHED …
https://stackoverflow.com/questions/36957028/difference-between-table-access-by-index-rowid-batched-and-table-access-by-index
Apr 29, 2016 . In the batched method oracle retrieves a few entries from the index, then first sorts them by the number of block, then process entries in the order determined by number of blocks: retrieves block 15, then retrieves rows 015-000123 and 015-000889 from this block; retrieves block 34, then retrieves row 034-000527 from this block
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Ric Ramblings: TABLE ACCESS BY INDEX ROWID BATCHED
https://ricramblings.blogspot.com/2013/12/table-access-by-index-rowid-batched.html
Dec 13, 2013 . table access by index rowid batched This looks like a pretty cool new way to use an index. From the documentation it say that this will access the index and get a “few rowids from the index, and then attempts to access rows in block order to improve the clustering and reduce the number of times that the database must access a block.”
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Difference between ROWID and ROWID BATCHED in Oracle
https://www.ktexperts.com/difference-between-rowid-and-rowid-batched-in-oracle/
Mar 16, 2021 . TABLE ACCESS BY INDEX ROWID BATCHED is new execution plan operation introduced in oracle 12c to improve performace by make efficient and minimal read writes to the disk. It is generally used for range queries. This operation genrally select few ROWIDs from the index and then try to access the rows in blcoks.
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Batched Table Access - Pythian Blog
https://blog.pythian.com/batched-table-access/
Nov 29, 2013 . If _optimizer_batch_table_access_by_rowid is set to FALSE on a session level, for example, then the plans generated by Oracle do not include BATCHED suffix in table access rowsource, but in run-time Oracle still uses multi-block IO in the same way as 11g does, i.e. 39 or 19 IO requests per one call and scattered reads of clustered table data are there as well!
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"Table access by index rowid" is slower than "table access
https://asktom.oracle.com/pls/apex/asktom.search?tag=table-access-by-index-rowid-is-slower-than-table-access-by-user-rowid
Jul 18, 2018 . --with ROWID type a_iface is records( t_ROWID ROWID); type t_iface is table of a_iface index by integer; r_iface t_face; cursor c1 is select rowid from big_table where rownum<200000; begin loop fetch c1 bulk collecct into r_iface limit 50000; exit when r_iface.count=0; forall i in 1..r_iface.count update /*+PARALLLE(16) BIG_TABLE SET COLA=VALUE1 , COLB=VALUE2 WHERE ROWID= …
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Query (much) slower with optimizer_features_enable=12.1.0
https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:9526253800346912243
Feb 08, 2016 . 1 1 1 TABLE ACCESS BY INDEX ROWID BATCHED POLICY (cr=4 pr=2 pw=0 time=378 us cost=4 size=35 card=1) 1 1 1 INDEX RANGE SCAN POLICY_PRIME (cr=3 pr=2 pw=0 time=342 us cost=3 size=0 card=1)(object id 855870)
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Why cost for TABLE ACCESS BY INDEX ROWID to high for only
https://asktom.oracle.com/pls/apex/asktom.search?tag=why-cost-for-table-access-by-index-rowid-to-high-for-only-one-row
Sep 01, 2015 . Why cost for TABLE ACCESS BY INDEX ROWID to high for only one row Dear Tom,I have problem with query on table have function base index. create index :create index customer_idx_idno on Customer (lower(id_no)) ; --- id_no varchar2(40) Query 1: execute time 0.031s but cost 5,149, 1 row returnselect * from customer where LOWER
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TABLE ACCESS BY INDEX ROWID taking huge amount of CPU cost
https://answers.sap.com/questions/7710810/table-access-by-index-rowid-taking-huge-amount-of-.html
Sep 17, 2010 . reads to table blocks and most of them most likely random will take time. The TABLE ACCESS BY INDEX ROWID itself is quite fast but if we do it. very often it could become expensive. The index could actually slow down your performance, a full table scan.
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Optimizer Access Paths - Oracle
https://docs.oracle.com/database/121/TGSQL/tgsql_optop.htm
To access a table by rowid, the database performs the following steps: Obtains the rowids of the selected rows, either from the statement WHERE clause or through an index scan of one or more indexes. Table access may be needed for columns in the statement not present in the index. Locates each selected row in the table based on its rowid
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Table Access by Rowid | Oracle Database Internal Mechanism
https://databaseinternalmechanism.com/2016/12/29/table-access-by-rowid/
Dec 29, 2016 . To access a table by rowid, Oracle first obtains the rowids of the selected rows, either from the statement’s WHERE clause or through an index scan of one or more of the table’s indexes and then locates each selected row in the table based on its rowid and fetches the records. 1.
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Example of using INDEX Hint in Oracle | Smart way of
https://smarttechways.com/2021/08/25/example-of-using-index-hint-in-oracle/
Aug 25, 2021 . About SandeepSingh DBA Hi, I am working in IT industry with having more than 10 year of experience, worked as an Oracle DBA with a Company and handling different databases like Oracle, SQL Server , DB2 etc Worked as a Development and Database Administrator.
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Troubleshooting | Started Learning Oracle | Page 2
https://desaitaral.wordpress.com/category/troubleshooting/page/2/
Nov 08, 2013 . Oracle 12c TABLE ACCESS BY INDEX ROWID BATCHED. November 8, 2013 Leave a comment. Few days back exploring 12c DB on my small VM found this little new feature. Here is the output from 11gR2.
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Wrong index column order causes performance problems
https://use-the-index-luke.com/sql/where-clause/the-equals-operator/slow-indexes-part-ii
The next step is the TABLE ACCESS BY INDEX ROWID operation. It uses the ROWIDs from the previous step to fetch the rows—all columns—from the table. Once the LAST_NAME column is available, the database can evaluate the remaining part of the where clause.
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Slow performance querying from all_arguments — oracle-tech
https://community.oracle.com/tech/apps-infra/discussion/4476598/slow-performance-querying-from-all-arguments
Oct 22, 2020 . Slow performance querying from all_arguments. I've noticed slow performance querying from all_arguments in a 19c PDB. Here's the example of the problematic query which takes more than 20 seconds: The action plan shows steps 2-6 taking most of the time. In a non-pdb 11g database the same query takes less than 1 second.
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JSON Multi value index in Oracle 21c - Ask TOM
https://asktom.oracle.com/pls/apex/asktom.search?tag=json-multi-value-index-in-oracle-21c&p_session=14809456767015
Nov 10, 2021 . Thanks for the question, Rajeshwaran. Asked: October 22, 2021 - 3:20 am UTC. Last updated: November 10, 2021 - 4:24 am UTC. Version: 21.0. Viewed 10K+ times!
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