Indexes and BW statistics

hello all,
What is meaning of Indexes and BW statistics?
Sneha

Please search the forum...these have been discussed in details.

Similar Messages

Index and statistics

for infoprovider, what is the problem to run the indicex, but not statistics them?

Statistics tell the optimizer things like how many values there, how similar or unique the values are, etc. The database optimizer uses the index and table statistics to make decisions about how best to execute the query, e.g. perform indexed reads of the table or a full table scan, or what order to read tables. The CBO (Cost Based Optimzer) is generally trying to find the execution plan that requires the fewest system resources, generally the fewest IOs (but there are other factors in the mix). It may examine hundreds or thousands of different execution plans to find wht it thinks is best.
Without any / good statistics the CBO may make bad choices about how to execute the query, that are not the most efficient.
When you drop and rebuild the indices, you lose the statistics which could easily result in bad choices by the CBO (Cost Based Optimizer).

Is reindexing and rebuilding statistics nessiary

I'm reducing the size of a SQL database from 115905 records to about 110000 records. My SQL server administrator is nowhere to be found. Is it critical to have the database rebuild
indexes and update statistics before I let users get back into the front end application and do regular work?
I've been doing these archives daily for a week and he rebuilds indexes and updates statistics each day before I let the users get in.

Since you deleted large no of records updatiing stats would be a good option .And if you rebuild index with full scan,which i dont think would be necessary to do after delete process,stats would automatically be updated .
More or less index rebuild depends on fragmentation >30 % you rebuild and between 30 and 10 you reorganize.
Since it is your daily task I would suggest you to look at Ola hallengren script
http://ola.hallengren.com/sql-server-index-and-statistics-maintenance.html
Please mark this reply as the answer or vote as helpful, as appropriate, to make it useful for other readers

Performance Problems - Index and Statistics

Dear Gurus,
I am having problems lossing indexes and statistics on cubes ,it seems my indexes are too old which in fact are not too old just created a month back and we check indexes daily and it returns us RED on the manage TAB.
please help

Dear Mr Syed ,
Solution steps I mentioned in my previous reply itself explains so called RE-ORG of tables;however to clarify more on that issue.
Occasionally,ORACLE Cost-Based Optimizer may calculate the estimated costs for a Full Table Scan lower than those for an Index Scan, although the actual runtime of an access via an index would be considerably lower than the runtime of the Full Table Scan,Some Imperative points to be considered in order to perk up the performance and improve on quandary areas such as extensive running times for Change runs & Aggregate activate & fill ups.
Performance problems based on a wrong optimizer decision would show that there is something serious missing at Database level and we need to RE_ORG the degenerated indexes in order to perk up the overall performance and avoid daily manual (RSRV+RSNAORA)activities on almost similar indexes.
For Re-organizing degenerated indexes 3 options are available-
1) DROP INDEX ..., and CREATE INDEX 
2)ALTER INDEX <index name> REBUILD (ONLINE PARALLEL x NOLOGGING)
3) ALTER INDEX <index name> COALESCE [as of Oracle 8i (8.1) only]
Each option has its Pros & Cons ,option 2 seems to be having lot of advantages to
Advantages- option 2
1)Fast storage in a different table space possible
2)Creates a new index tree
3)Gives the option to change storage parameters without deleting the index
4)As of Oracle 8i (8.1), you can avoid a lock on the table by specifying the ONLINE option. In this case, Oracle waits until the resource has been released, and then starts the rebuild. The "resource busy" error no longer occurs.
I would still leave the Database tech team be the best to judge and take a call on these.
These modus operandi could be institutionalized for all fretful cubes & its indexes as well.
However,I leave the thoughts with you.
Hope it Helps
Chetan
@CP..

Which Event Classes i should use for finding good indexs and statistics for queries in SP.

Dear all,
I am trying to use pro filer to create a trace,so that it can be used as workload in
"Database Engine Tuning Advisor" for optimization of one stored procedure.
Please tel me about the Event classes which i should use in trace.
The stored proc contains three insert queries which insert data into a table variable,
Finally a select query is used on same table variable with one union of the same table variable, to generate a sequence for records based on certain condition of few columns.
There are three cases where i am using the above structure of the SP, so there are three SPS out of three , i will chose one based on their performance.
1) There is only one table with three inserts which gets into a table variable with a final sequence creation block.
2) There are 15 tables with 45 inserts , which gets into a tabel variable with a final
sequence creation block.
3)
There are 3 tables with 9 inserts , which gets into a table variable with a final
sequence creation block.
In all the above case number of record will be around 5 lacks.
Purpose is optimization of queries in SP
like which Event Classes i should use for finding good indexs and statistics for queries in SP.
yours sincerely

"Database Engine Tuning Advisor" for optimization of one stored procedure.
Please tel me about the Event classes which i should use in trace.
You can use the "Tuning" template to capture the workload to a trace file that can be used by the DETA. See
http://technet.microsoft.com/en-us/library/ms190957(v=sql.105).aspx
If you are capturing the workload of a production server, I suggest you not do that directly from Profiler as that can impact server performance. Instead, start/stop the Profiler Tuning template against a test server and then script the trace
definition (File-->Export-->Script Trace Definition). You can then customize the script (e.g. file name) and run the script against the prod server to capture the workload to the specified file. Stop and remove the trace after the workload
is captured with sp_trace_setstatus:
DECLARE @TraceID int = <trace id returned by the trace create script>
EXEC sp_trace_setstatus @TraceID, 0; --stop trace
EXEC sp_trace_setstatus @TraceID, 2; --remove trace definition
Dan Guzman, SQL Server MVP, http://www.dbdelta.com

Gathering statistics on interMedia indexes and tables

Has anyone found any differences (like which one is better or worse) between using the ANALYZE sql command, dbms_utility package, or dbms_stats package to compute or estimate statistics for interMedia text indexes and tables for 8.1.6? I've read the documentation on the subject, but it is still unclear as to which method should be used. The interMedia text docs say the ANALYZE command should be used, and the dbms_stats docs say that dbms_stats should be used.
Any help or past experience will be grateful.
Thanks,
jj

According to the Support Document "Using statistics with Oracle Text" (Doc ID 139979.1), no:
Q. Should we gather statistics on the underlying DR$/DR# tables? If yes/no, why?
A. The recommendation is NO. All internal recursive queries have hints to fix the plans that are deemed most optimal. We have seen in the past that statistics on the underlying DR$ tables may cause query plan changes leading to serious query performance problems.
Q. Should we gather statistics on Text domain indexes ( in our example above, BOOKS_INDEX)? Does it have any effect?
A: As documented in the reference manual, gathering statistics on Text domain index will help CBO to estimate selectivity and costs for processing a CONTAINS() predicate. If the Text index does not have statistics collected, default selectivity and cost will be used.
So 'No' on the DR$ tables and indexes, 'yes' on the user table being indexed.

What is the difference between the drop and create the index and rebuild index ?

Hi All,
what is the difference between drop and create index & rebuild index ? i think both are same...Please clarify if both are same or any difference...
Thanks in Advance,
rup

Both are same. Rebuilding an index drops and re-creates the index.
Ref:
SSMS - https://technet.microsoft.com/en-us/library/ms187874(v=sql.105).aspx
TSQL - https://msdn.microsoft.com/en-us/library/ms188388.aspx
I would suggest you to also refer one of the best index maintenance script as below:
https://ola.hallengren.com/sql-server-index-and-statistics-maintenance.html

BITMAP index and BLEVEL

Hi All,
We have one BITMAP index on a flag column (Y/N).Table is non partitioned with 3.4 million records.
Following are index stats.
select INDEX_NAME,INDEX_TYPE,BLEVEL,LEAF_BLOCKS,DISTINCT_KEYS,CLUSTERING_FACTOR,NUM_ROWS,SAMPLE_SIZE,DEGREE FROM DBA_INDEXES WHERE
INDEX_NAME='LATE_VER_FLG_CAX_IDX' AND OWNER='EQHUB'
INDEX_NAME           INDEX_TYPE     BLEVEL LEAF_BLOCKS DISTINCT_KEYS CLUSTERING_FACTOR   NUM_ROWS SAMPLE_SIZE DEGREE
LATE_VER_FLG_CAX_IDX BITMAP             11         716             2             72783      72783       72783 1
select last_analyzed,sample_size,num_rows from dba_indexes where index_name='LATE_VER_FLG_CAX_IDX';
LAST_ANALYZED      SAMPLE_SIZE   NUM_ROWS
31.Jan.09/00:29:41       72783      72783
NAME                      HEIGHT     BLOCKS    LF_ROWS    LF_BLKS LF_ROWS_LEN    BR_ROWS    BR_BLKS DEL_LF_ROWS DISTINCT_KEYS BTREE_SPACE USED_SPACE   PCT_USED
LATE_VER_FLG_CAX_IDX          12       4352          0          0                      1          1           0             0        8028
CREATE BITMAP INDEX "EQHUB"."LATE_VER_FLG_CAX_IDX" ON "EQHUB"."BBO_CORPORATE_ACTIONS" ("LATEST_VERSION_FLAG")
PCTFREE 10 INITRANS 2 MAXTRANS 255 COMPUTE STATISTICS
STORAGE(INITIAL 65536 NEXT 2097152 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT)
TABLESPACE "ETDHUB_EQHUB_INDEX"
SQL> select LATEST_VERSION_FLAG,count(*) from BBO_CORPORATE_ACTIONS group by LATEST_VERSION_FLAG;
L   COUNT(*)
N    2265303
Y    1189116I am wondering
1.What can be done to reduce index BLEVEL/HEIGHT? (i assume COALESCE will not help)..Should i rebuild the index?
2.Why BTREE_SPACE is only showing 8028 where dba_segments is showing index size =34 MB?
3.Why PCT_USED is NULL?
Is that so BLEVEL/PCT_USED not relative for BITMAP Indexes?
I found that no query is using this index for last 60 days and performance is getting degraded due to FTS.
Should i REBUILD the index so that i can reduce BLEVEL/HEIGHT/INDEX_SIZE and improve query performance with INDEX ACCESS.
Regards,
Bhavik Desai

Bhavik Desai wrote:
You perfectely caught the DML pattern.There are 4 daily ELT jobs which INSERT 300 and UPDATE 250 records/execution.
May i ask you,upon which observation,you point this?Also it would be greate if you tell me how did you calculate 67% PCT_FREE.
This was based on the fact that an update to a single row in a table could result in a copy of an entire bitmap index chunk being made; so you need to leave a lot of space free in the leaf blocks to allow for these copies because you really don't want to cause an index leaf block split to occur - especially since that would tend to cascade up the index and cause a branch block split as well. On this basis, pctfree 51 should be adequate for most cases, but setting it to 67 (a) allows you to do a couple of updates/clones to the same chunk before you hit a problem, and (b) helps to keep the chunks smaller which helps to reduce the undo and redo a bit.
This has just reminded me of a little detail - I am a little surprised by the fact that you got an index into this state in 10.2, because that release of Oracle seems to avoid creating a long chain of clones of the same index chunk when you do a series of small updates, and it is the chain of clones that results in branch blocks split running up the index and exploding it to an enormous height. Has this database been upgraded from 9i (or even 10.1) some time in the fairly recent past ?
>
I still dont understand,
1.Why there is no difference in BTREE_SPACE?
2.Why PCT_USED is NULL?
I've just run a quick test on 10.2.0.1 and 10.2.0.3 creating a table with a y/n/null column and creating a bitmap index on it. The results from index_stats didn't match across versions, and the 10.2.0.3 stats were clearly garbage - very similar to yours. For the moment I would assume that something has been broken in 10.2.0.3 with this use of the validate command.
>
If we consider Franck Pachot's observation,then it would be better to convert the BITMAP to BTREE.Is this a normal bitmap behavior?Randolf's observation about the numbers of rows involved is most relevant: it doesn't look like an index that the optimizer should consider using for anything other than select flag, count(*), and changing from a bitmap to a btree won't make any difference. In other words, unless you can point to an important piece of code and say "it makes tis bit run much better" maybe the index shouldn't exist at all.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
"The temptation to form premature theories upon insufficient data is the bane of our profession."
Sherlock Holmes (Sir Arthur Conan Doyle) in "The Valley of Fear".

What is diff b/w sy-index and sy-tabix

Hi all,
Can u plz give me the diff b/w sy-index and sy-tabix exactly and how it works.
Thanks & Regards
Venkat

Hi Venkat,
1.SY-INDEX
->Current loop pass
->In a DO or WHILE loop, SY-INDEX contains the number of loop passes including the current pass.
2.SY-TABIX
->Current line index
Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables.
The field is either not set or is set to 0 for hashed tables.
APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table.

COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.
LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE.
READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry.

SEARCH <itab> FOR sets SY-TABIX to the index of the table line in which the search string is found.
I think that it clears ur doubt.
Thanks,
Venkat.O

What is difference between sy-index and sy-tabix and where both are using ?

what is difference between sy-index and sy-tabix and where both are using ?

hi nagaraju
sy-tabix is in Internal table, current line index. So it can only be used while looping at the internal table.
sy-index is in Loops, number of current pass. This you can use in other loop statements also (like do-enddo loop, while-endwhile)
SY-INDEX is a counter for following loops: do...enddo, while..endwhile
SY-TABIX is a counter for LOOP...ENDLOOP, READ TABLE...
Here is an example from which you can understand the difference between sy-tabix and sy-index.
Itab is an internal table with the following data in it.
id Name
198 XYZ
475 ABC
545 PQR.
loop at itab where id > 300.
write :/ itab-id, itab-name , sy-tabix, sy-index.
endloop.
My output will be :
475 ABC 2 1
545 PQR 3 2
Sy-tabix is the index of the record in internal table.
sy-index gives the no of times of loop passes.
So, for the first record in the output (475 ABC), 2 is the index of the record in internal table and as it is first time loop pass occured, sy-index value is 1.
Regards,
navjot
award points

Difference b/w sy-index and sy-tabix

hai all,
Could u explain the difference b/w sy-index and sy-tabix?
regards,
Selva

Hi,
sy-index - For Loops, Current Loop Pass.
sy-tabix - For Internal Table, Current Line Index in internal table.
sy-tabix is used at internal table operations (READ TABLE ... LOOP AT ...), sy-index is used at cycles (DO...n TIMES).
SY-TABIX:
Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables. The field is either not set or is set to 0 for hashed tables.
it can be set by using the following:
1.append
2.collect
3.loop at
4. read
5.search
APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table.
COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.
LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE.
READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry.
SEARCH <itab> FOR sets SY-TABIX to the index of the table line in which the search string is found.
SY-INDEX:
SY-INDEX is used to describe the number of iteration with in the DO..ENDDO, WHILE ...ENDWHILE....
for example,
DO.
WRITE SY-INDEX.
IF SY-INDEX = 3.
EXIT.
ENDIF.
ENDDO.
it gives output as:
1 2 3
Regards,
Raj.

Regarding sy-index and sy-tabix

Hi,
What is the major difference between sy-index and sy-tabix ,
can you give me one good example with code..
Regards,
Reddy.

Hi,
SY-TABIX - Current line of an internal table. SY-TABIX is set by the statements below, but only for index tables. The field is either not set or is set to 0 for hashed tables.
APPEND sets SY-TABIX to the index of the last line of the table, that is, it contains the overall number of entries in the table.
COLLECT sets SY-TABIX to the index of the existing or inserted line in the table. If the table has the type HASHED TABLE, SY-TABIX is set to 0.
LOOP AT sets SY-TABIX to the index of the current line at the beginning of each loop lass. At the end of the loop, SY-TABIX is reset to the value that it had before entering the loop. It is set to 0 if the table has the type HASHED TABLE.
READ TABLE sets SY-TABIX to the index of the table line read. If you use a binary search, and the system does not find a line, SY-TABIX contains the total number of lines, or one more than the total number of lines. SY-INDEX is undefined if a linear search fails to return an entry.
SEARCH FOR sets SY-TABIX to the index of the table line in which the search string is found.
SY_INDEX - In a DO or WHILE loop, SY-INDEX contains the number of loop passes including the current pass.
sy-tabix is the tab index - the index of the record in the internal table you are accessing,
sy-index is the loop counter.
If you use a condition in LOOP the sy-index will go from 1 to n, but sy-tabix will refer to the line in the internal table.
Hope this helps u.
Thanks,
Ruthra

Difference b/w index and key

can you please tell me the difference between the follwing UI elements
1.dropdownbykey and dropdownbyindex
2.radiobutton group by key and radio button group by index
and also tell me in which case which UI need to be used
Thanks
rahul

DropDownByKey
A DropDownByIndex UI element provides the user with a dropdown list box. You cannot select more than one entry from the selection list. The UI element consists of a text field, a button, and a selection list. Any list item already selected is displayed in the text field. When the user chooses the pushbutton, a list of all possible values is displayed.
DropDownByIndex
A DropDownByIndex UI element provides the user with a dropdown list box. You cannot select more than one entry from the selection list. The UI element consists of a text field, a button, and a selection list. Any list item already selected is displayed in the text field. When selecting the button, a list with all possible values is displayed.
http://help.sap.com/saphelp_nw04s/helpdata/en/d9/478041a17e060de10000000a1550b0/frameset.htm
In radiabutton we can have the only one decision.But
checkbox we can have mulitiple options.
based on the usage we choose these controls.
for example,
RadioButton
Gender - o Male o Female
here we can select only one option
for example,
CheckBox
your Interested Games?
o cricket o football o valleyball o hockey
here use may have more than option.
i hope this is enough.
award the point if ans is help full.

Difference b/w index and unique

Hi,
Difference b/w index and unique?

hi,
The optional additions UNIQUE or NON-UNIQUE determine whether the key is to be unique or non-unique, that is, whether the table can accept duplicate entries. If you do not specify UNIQUE or NON-UNIQUE for the key, the table type is generic in this respect. As such, it can only be used for specifying types. When you specify the table type simultaneously, you must note the following restrictions:
You cannot use the UNIQUE addition for standard tables. The system always generates the NON-UNIQUE addition automatically.
You must always specify the UNIQUE option when you create a hashed table.
INDEX:
An index can be considered a copy of a database table that has been reduced to certain fields. This copy is always in sorted form. Sorting provides faster access to the data records of the table, for example using a binary search. The index also contains a pointer to the corresponding record of the actual table so that the fields not contained in the index can also be read.
The primary index is distinguished from the secondary indexes of a table. The primary index contains the key fields of the table and a pointer to the non-key fields of the table. The primary index is created automatically when the table is created in the database
You can also create further indexes on a table in the ABAP Dictionary. These are called secondary indexes. This is necessary if the table is frequently accessed in a way that does not take advantage of the sorting of the primary index for the access.
Indexes speed up data selection from the database. They consist of selected fields of a table, of which a copy is then made in sorted order. If you specify the index fields correctly in a condition in the WHERE or HAVING clause, the system only searches part of the index (index range scan).
The system automatically creates the primary index. It consists of the primary key fields of the database table. This means that for each combination of fields in the index, there is a maximum of one line in the table. This kind of index is also known as UNIQUE.
If you cannot use the primary index to determine the result set because, for example, none of the primary index fields occur in the WHERE or HAVINGclauses, the system searches through the entire table (full table scan). For this case, you can create secondary indexes, which can restrict the number of table entries searched to form the result set.
You create secondary indexes using the ABAP Dictionary. There you can create its columns and define it as UNIQUE. However, you should not create secondary indexes to cover all possible combinations of fields.
Only create one if you select data by fields that are not contained in another index, and the performance is very poor. Furthermore, you should only create secondary indexes for database tables from which you mainly read, since indexes have to be updated each time the database table is changed. As a rule, secondary indexes should not contain more than four fields, and you should not have more than five indexes for a single database table.
If a table has more than five indexes, you run the risk of the optimizer choosing the wrong one for a particular operation. For this reason, you should avoid indexes with overlapping contents.
Secondary indexes should contain columns that you use frequently in a selection, and that are as highly selective as possible. The fewer table entries that can be selected by a certain column, the higher that columns selectivity. Place the most selective fields at the beginning of the index. Your secondary index should be so selective that each index entry corresponds to, at most, five percent of the table entries. If this is not the case, it is not worth creating the index. You should also avoid creating indexes for fields that are not always filled, where their value is initial for most entries in the table.
If all of the columns in the SELECT clause are contained in the index, the system does not have to search the actual table data after reading from the index. If you have a SELECT clause with very few columns, you can improve performance dramatically by including these columns in a secondary index.
What is the difference between primary index and secondary index?
http://help.sap.com/saphelp_47x200/helpdata/en/cf/21eb2d446011d189700000e8322d00/frameset.htm
A difference is made between Primary & Secondary indexes to a table. the primary index consists of the key fields of the table and a pointer to the non-keys-fields of the table. The Primary index is generated automatically when a table is created and is created in the datebase as the same times as the table. It is also possible to define further indexes to a table in the ABAP/4 dictionary, which are then referred to as Secondary indexes.
Message was edited by:
Roja Velagapudi

What is RID in non clustered index and its use

Hi All,
I need help regarding following articles on sql server
1) what is RID in non clustered index and its use.
2) What is Physical and virtual address space. Difference in 32 bit vs 64 bit Virtual address space
Regards
Rahul

Next time Please ask single question in a thread you will get better response.
1. RID is location of heap. When you create Non clustered index on heap and
lookup happens to get extra records RID is used to locate the records. RID is basically Row ID. This is basic definition for you. Please read
this Thread for more details
2. I have not heard of Physical address space. I Know Virtual address space( VAS)
VAS is simple terms is amount of memory( virtual ) 'visible' to a process, a process can be SQL Server process or windows process. It theoretically depends on architecture of Operating System. 32 bit OS will have maximum range of 4 G VAS, it's calculated
like a process ruining on 32 bit system can address max up to 2^32 locations ( which is equivalent to 4 G). Similarly for 64 bit max VAS will be 2^64 which is theoretically infinite. To make things feasible maximum VAS for 64 bit system is kept to 8 TB. Now
VAS acts as layer of abstraction an intermediate .Instead of all request directly mapping to physical memory it first maps to VAS and then mapped to physical memory so that it can manage request for memory in more coordinated fashion than allowing process
to do it ,if not it will soon cause memory crunch.Any process when created on windows will see virtual memory according to its VAS limit.
Please read
This Article for detailed information
Please mark this reply as answer if it solved your issue or vote as helpful if it helped so that other forum members can benefit from it
My Technet Wiki Article
MVP

Indexes and BW statistics

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