Performance Tuning :: How Expensive (speed) Is Unique Versus Primary Key In Large Table
Aug 15, 2011
I have two design alternatives and need to understand how expensive (speed) is one of them against the other for a medium size table (100K-200K records):
create table xyz
(
f1 number not null,
f2 varchar2(20) not null,
f3 number not null,
f4 varchar2(50),
[code]....
the idea is to optimize the design by using a PK instead of the 3 keys and there is a debate that searching a unique index field(2nd scenario) is of the same speed than searching a PK field (1st scenario).
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Dec 9, 2011
If you have 3 tables (yr09, yr10,yr11) one with 2009 data, 2010 and 2011 data respectively. And a view (vw_yr091011) with a "union all" on all three.
Question: Will the performance be same for the following two queries ?
Question: Will Oracle read all 3 tables in the view when we search for only one year ?
select count(*) from yr09
where year = 2009;
-- vs
select count(*) from vw_yr091011
where year = 2009;
The following link says yes, the performance remains the same.
Link: [URL]..........
when I tried on a volume of 14000 records. The count came out same but the view took 50 more sec. And the explain plan shows it accessed all three tables.
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Aug 26, 2011
I am working with an online application with the database in Oracle 10G. We have a table with 10 million rows and this table is subjected to grow in future also. Moreover we cannot archive some of these rows as these records are required for referencing.
We have all necessary indexes on the table but querying this table takes a lot of time especially when it is joined with other tables. some methods with which I can manage this table in a better way so that queries joining this table would execute faster..
SELECT
TAB1.C6,
TAB1.C8,
TAB1.C10,
TAB3.C4,
[code]....
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Jun 2, 2011
I am gathering stats by using below block i.e., for some 3 million records and there are 6 indexes on the table. What is the relevance of value 4 here (i.e., method_opt => 'FOR ALL INDEXED COLUMNS SIZE 4')? If I increase 4 to 250 will there be any speed change in gathering stats. My intention is to speed up the gathering of stats.
begin
dbms_stats.gather_table_stats(
ownname => SYS_CONTEXT('USERENV', 'CURRENT_SCHEMA'),
tabname => 'LEGAL_VIEW_TARGET',
method_opt => 'FOR ALL INDEXED COLUMNS SIZE 4',
cascade => TRUE
);
END;
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Mar 28, 2011
I have several large tables in the live system! Those table are store historical information.
current situation:
Now, A table record was 129 million rows.
Every month added 4.5M records to this table.
This table data size 17GB and index size 28GB.
I have only 30 GB available free space on disk!
How to split this table to small pieces (partition table by month)?
What is the best approach?
I would like to do partitioning on this table month by month.
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Oct 24, 2013
How To Increase Data Retrieval / Insertion Speed my data base has more than 0.5 million records Forms Some Time Respond Very Slow .
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Aug 4, 2010
I have normal tables with hugh Data and would like to increase the performace by following means:
1) Add a new column in each table. Say this column Name is IS_LIVE. This new column have only two value 1 ( LIVE ) OR 0 ( NOT LIVE ).
2) Change the normal tables to Partitioned table. There would be only two partitioned in all the table. The partitioned key column would be IS_LIVE and both partitioend recrods would be in two different tablespace.
3) Added a POLICY function to these partitioned table to Always add a Query Predicate of '1' to all queuries.
I am interested to know that what kind of Indexes ( Global Or local ) would be suitable for these kind of Design.Is there any use of having Local index on IS_LIVE.Please note that Primary Key doesnot have this new column in it.
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Feb 4, 2011
I've got a query running a select count (*) over a table. The default plan takes in the order of 15 minutes to return, a hinted plan to use a different index takes 3 minutes to return.
Unfortunately I cant get at the index stats and a few other areas which I suspect may be key here.When running autotrace against the two queries I see fairly different values as one would expect.
Query
select count (*) from fulfilmentitem bfi where created >= sysdate-30 AND bfi.status = 'FA' AND bfi.fulfilmentmethod = 'D'
Slow run
PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
----------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 15 | 33119 (1)|
| 1 | SORT AGGREGATE | | 1 | 15 | |
|* 2 | TABLE ACCESS BY INDEX ROWID| FULFILMENTITEM | 12525 | 183K| 33119 (1)|
|* 3 | INDEX RANGE SCAN | IDX_FULFIL_METHODSTATUS | 250K| | 1786 (1)|
----------------------------------------------------------------------------------------------
[code]....
IDX_FULFIL_METHODSTATUS is across FULFILMENTMETHOD & STATUS in that order.
IDX_BFI_CREATED is on CREATED and is approx 70% of the size of the other index
The row counts estimated in the explain plan are out, the count(*) comes in at 32.8k rows.As you will have seen, the fast run shows a pretty significant consistent get increase compared to the slow run and a decent though not dramatic physical read drop.
My uncertainty is around if these changes in consistent get/phys read values would typically be enough to suggest the real time improvements I'm observing or if other (albeit perhaps temporary) factors are involved. It is a prod OLTP environment so the data will be rapidly changing and that may be a factor.
I know it can never be an exact science without intimately knowing the hardware/current loads etc but I also know that there's enough experience on these boards to have a loose handle on if the time shifts between queries are likely (or not) to be reflective of the stat changes or if those differences alone shouldn't (or typically wouldn't account) for it.
I'm thinking about instructing the query to ignore its original plan but am hesitant to do so without being a little more confident that it's not just a timing thing or something other than the change of index approach which may be causing the improvement. the autotrace stat changes observed I couldn't put my hand on heart say "yup - that change is good, ignore the default index all the time for this job".
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Jun 28, 2011
I have a huge table (about 60 gb) partition over range. The index on this table is global index created on 4 columns together. I have a query which is running very slowly. The explain plan is showing the use of this global index.Explain plan is not showing pstart and pend because the index is global.
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Jan 27, 2011
I was comparing cost of rebuild vs create index...I carried out the following test
SQL> create table t4 as select * from t1;
Table created.
SQL> create table t5 as select * from t1 where 1=2;
Table created.
SQL> create index i5 on t5(id);
Index created. SQL> select bytes,extents,blocks from user_segments where segment_name='I5';
BYTES EXTENTS BLOCKS
---------- ---------- ----------
65536 1 8
SQL> alter index i5 unusable;
Index altered.
SQL> alter table t5 nologging;
Table altered.
SQL> Alter session set skip_unusable_indexes=True;
Session altered.
SQL> insert /*+ append */ into t5 select * from t1;
563904 rows created.
SQL> commit;
Commit complete.
Now I compared the cost (elapsed time, logical I/O) of the operations
create index i4 on t4(id);
Vs
alter index i5 rebuild online;
Following is the related trace of above 2 steps
create index i4 on t4(id)
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 1 0 0
Execute 1 1.17 3.38 9497 7869 335 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 1.17 3.38 9497 7870 335 0
Misses in library cache during parse: 1
Optimizer goal: CHOOSE
Parsing user id: 5
[code]....
So which option we shall pick in such cases? {Of course I haven't set 'nologging' for the indices but it is same for both indices we are comparing}
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Jan 19, 2011
I want to load 10 millions records from staging table to master table.One logic must be take during the load, the logic is rows already present in master table means, we need to update corresponding rows in master table otherwise rows insert in target table.
I have been using bulk collect and forall method to load data. it shows better performance compare then cursor row by row process. As per oracle doucmentation, we cannot use SELECT statements inside FORALL condition so we could not use logic inside the forall condition.
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May 7, 2011
I am currently in the favorable situation in which I have excess amounts of memory available on the database server - a single node setup. The server only serves the single instance and no other processing. Database size is around 2.3tb and memory is 50gb. For the majority of processing, AIX is allocating a significant amount (anywhere from 30-40%) of the memory to the AIX file system cache (persistent pages).
I've been trying to find documentation about this, but have not had any luck yet. My guess is that it would be better to allow Oracle to cache this data - meaning increase the SGA target and max size to allow for a larger buffer cache. However, the nice thing about the AIX cache is if process memory is needed, the file system cache gives up pages. If the memory was allocated to the SGA, its pretty much locked in.
I have read several articles stating that a larger buffer cache is not always better, as a larger cache takes more management. But having both of the caches active seem to be a waste of memory, effectively storing the data twice - once in AIX persistent pages and a second time in Oracle database buffer cache.
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Aug 18, 2010
How does standard vs advanced handle index compression? Is there an advantage to having one vs the other besides the incurred cost?
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Jun 14, 2012
Is there any hint to force "Index Unique Scan" over "Index Range Scan".
My query is generating different plans with the above two, and very slow when it uses "Index Range Scan".
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Apr 5, 2012
Create small functional indexes for special cases in very large tables.
When there is a column having one values in 99% records and another values that have to be search for, it is possible to create an index using null value. Index will be small and the rebuild fast.
Example
create index vh_tst_decode_ind_if1 on vh_tst_decode_ind
(decode(S,'I','I',null),style)
It is possible to do index more selective when the key is updated and there are many records to create more levels in b-tree.
create index vh_tst_decode_ind_if3 on vh_tst_decode_ind
(decode(S,'I','I',null),
decode(S,'I',style,null)
)
To access the record can by like:
SQL> select --+ index(vh_tst_decode_ind_if3)
2 style ,count(*)
3 from vh_tst_decode_ind
4 where
5 decode(S,'I','I',null)='I'
6 group by style
7 ;
[code]....
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Jan 20, 2012
when I check one database, I noticed that the primary key constraint is in UNUSABLE status. But when I check the table, the table DDL itself,the below query mentioned.
ALTER INDEX "COMMON_DATA"."PK_DISE_MOBILE" UNUSABLE ENABLE
suggest whether I need rebuild this index? if I rebuild this index, will it useful for me for the performance improvement? But the table has only 578234 records.
Table DDL
CREATE TABLE "COMMON_DATA"."DISE_MOBILE_INSTALLATION"
( "M_DBASE_ID" VARCHAR2(2),
"COMPANY_NUMBER" NUMBER(3,0),
"M_ACCT_ID" NUMBER(8,0),
"ACCOUNT_CREATION_DATE" DATE,
"ORDER_NUMBER" VARCHAR2(15),
"ORDER_CREATION_DATE" DATE,
"ORDER_CREATION_METHOD" VARCHAR2(1),
"CONTRACT_TERM" VARCHAR2(3),
"GROUP_ID" VARCHAR2(6),
[code]...
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Apr 30, 2013
about the functionalty w.r.t. unique constraint and Distinct clause. Below is the example which is confusing me lot.
--Below statement will create table and unique constraint
Create Table A (A Varchar2 (10) Unique);
Insert Into A Values (Null);
Insert Into A Values (1);
Insert Into A Values (2);
[code]...
If we are saying each null value is having a unique value, then why oracle distinct showing records.
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Mar 4, 2010
Is there anyway to speed up the performance of the go_record built it or is there an alternative way to do it.
I have a table with nearly 30,000 rows and I would like to implement a text field that will allow the user to jump to a specified record. The only problem is if they try to jump too far away it will take a long time to load (beginning to end of 30,000 takes over a minute).
This problem doesn't arise if all the records, or up to the one they are jumping to, have been fetched already, but even if I fetch all records at the beginning it will still take a long time to initially load them.
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Oct 31, 2011
I have two tables with 113M records in DWH_BILL_DET & 103M in prd_rerate_chg_que and Im running following merge query, which is running for 13 hrs to update records, which is quiet longer time.
SQL> explain plan for MERGE /*+ parallel (rq, 16) */
INTO DWH_BILL_DET rq
USING (SELECT rated_que_rowid,
detail_rerate_flag_code,
rerate_sel_key,
[code].....
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Dec 10, 2010
what is difference between primary key and unique+not null
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Nov 28, 2010
A Master form in a tabular format. Id is a display item. I want to auto generate Id with following query.
select nvl(max(issue_id),0)+1 into :issue_mt.issue_id from issue_mt;
It works:
1)When each record is saved before creating new record.
It doesn't work:
2)If multiple records are entered with out saving each record.
What to do to generate unique Id in both cases?
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Jun 27, 2012
I have in a plsql block somewhere a statement like
INSERT INTO TABLE1( id , col)
SELECT id, col
FROM TABLE2;
This statement returns an error ORA-00001: unique constraint because id is a primary key on TABLE1. I would like to know what is the value of id that raised the exception.
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Jan 14, 2013
I'm trying to make a foreign key against a table which has a unique index instead of a primary key.
i get this error:
Error SQL: ORA-02270: no matching unique or primary key for this column-list
02270. 00000 - "no matching unique or primary key for this column-list"
*Cause: A REFERENCES clause in a CREATE/ALTER TABLE statement gives a column-list for which there is no matching unique or primary key constraint in the referenced table.
my question is (i've searched several times with no results) can i create a foreign key with a table wich has no primary key but a unique index ?example:
CREATE TABLE TABLE1(
IDTABLE1 NUMBER(5),
NAME VARCHAR2(30)
);
CREATE TABLE TABLE2(
[code]....
or TABLE1.IDTABLE1 must be a 'Primary Key' instead of unique index ?I know it should be primary, but i need to know if it would work with the index somehow. The reason is i'm migrating a large database and the original structure in mysql uses fk with indexes and no pks in some tables (48 to be precise)
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Jul 6, 2010
I was cloning a schema user1 as user2 in the same database.
user1 had quota on 2 tablespaces user1_data and user1_index.
I created user with name as user2.
I created tablespace user2_data only and granted user2 unlimited quota on that tablespace only (did not grant him 'resource' role or unlimited tablespace privilege) Now exported user1 schema as follows
exp system/<passowrd> file=/u05/oradata/dump/user1_schema.dmp log=/u05/oradata/dump/user1_schema_exp.log owner=user1 rows=y constraints=y triggers=y indexes=y statistics=none recordlength=65535 compress=no consistent=n grants=y
then imported in in user2 schema as follows
imp system/<password> file=/u05/oradata/dump/user1_schema.dmp log=/u05/oradata/dump/user2_schema_imp.log fromuser=user1 touser=user2 rows=y constraints=y indexes=y statistics=none recordlength=65535 grants=y
during import i encountered following errors for so many constraints
"ALTER TABLE "table2" ADD CONSTRAINT "constraint_name1" FOREIGN KEY ("CTR_ID") REFERENCES "table1" ("CTR_ID") ENABLE NOVALIDATE"
IMP-00003: ORACLE error 2270 encountered
ORA-02270: no matching unique or primary key for this column-list
IMP-00017: following statement failed with ORACLE error 2270:
I found that the it happened as the primary key of table1 was not created for which error was logged in the log file
. . importing table "table1" 19441 rows imported
IMP-00015: following statement failed because the object already exists:
"ALTER TABLE "table1" ADD CONSTRAINT "T1_PK79" PRIMARY KEY ("CTR_"
"ID") USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 STORAGE(INITIAL 65536 F"
"REELISTS 1 FREELIST GROUPS 1) TABLESPACE "USER1_INDEX" LOGGING ENABLE "
. . importing table "table5" 0 rows imported
However, I checked that the T1_PK79 does not exist in the user2 schema though it exists in user1 schema Neither the index for priamry key (T1_PK79) existed in user2 schema not the table <table1> existed before this import Then what could be the reason that I am getting an error "IMP-00015: following statement failed because the object already exists"?
I assume tablespace for index would not be an issue here as other indexes got created properly in user2_index tablespace during this import.
I tried this twice, once with user2 schema and then with user3 schema as well (with different tablespace), but result is the same.
There were no users connected to the database during export and no background jobs were modiying any data in schema user1 while export.
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Oct 7, 2013
We have a large table of equally sized data blobs in our Oracle system and we'd like to select the whole table once into the memory. The corresponding tablespace is stored in SSD fast disks and is managed by ASM. However the achievable select speed (reading data into memory) of Oracle is not satisfactory. When we store the data in SSD disk using custom methods (e.g. in SQLite DB files) and load then into memory by multithreading (8 thread) techniques, the speed is more than 15 times that of Oracle.
Is there any way to optimize the oracle and ASM for increased full table select in our case. We tried FULL TABLE SCAN and PARALLEL hints and DB_FILE_MULTIBLOCK_READ_COUNT too, but with no success.
FYI:Our data blob is about 4.2kB and each DB_BLOCK_SIZE is 8kB. The ASM segment is configured for AUTO-ALLOCATE. The table is partitioned by HASH. Our oracle system is not RAC.
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Feb 6, 2011
I am trying to update columns of Table A with the columns of Table B. Both these tables have 60,000 rows each. I tried this operation using following 2 queries:
Query 1
Update TableA A
set
(A.col1,A.col2,A.col3)=(select B.col1,B.col2,B.col3
from TableB
where A.CODE=B.CODE)
Query 2
Update TableA A
set
(A.col1,A.col2,A.col3)=(select B.col1,B.col2,B.col3
from TableB
where A.CODE=B.CODE)
where exists
A.code = (select B.code
from TableB B
where A.code=B.code)
When i execute these two above queries, it keeps executing indefinitely.
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Dec 9, 2008
Environment Setup
Oracle Server 11g on HP-UX
Oracle Client on Windows
I am using swingbench tool to generate load on DB and using OLTP like benchmark i am comparing the performance of plain data and encrypted data.
I have created two different database. one for tde and other for plain. I have populated same number of rows in both databases. Then i start running the benchmark and i use SAR to collect disk I/O's, VSAR to CPU usage.
From the sar report it seems that,
Oracle plain has faster transactions, it uses minimum CPU. But when look in tot the Reads/Writes TDE has lower than the plain.
If TDE needs to encrypt the data to store in the disks it should occupy more space than the plain data. Then the I/O should be more in TDE..
Note: Bcz the DB parameters are same, number of rows in the tables are same. File system and its block size are same. I will run the swingbench seperately for both the databases.
I am attaching the excel sheet for sar results. Let me know if you need more information
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Jul 20, 2010
With a very large database (VLDB) for a data warehouse (DW) using primarily a STAR based schema in an environment in which time (both human and CPU) is orders of magnitude more valuable than storage capacity, is there any signficant difference in query performance when tables have all fixed length (CHAR) columns compared to tables with variable length (VARCHAR2) columns?
I realize this is one of those "in general" questions so considering "a given VLDB DW environment" with all other things being equal, what, if any, is the time based performance difference between a database of tables with all fixed sized columns versus one of tables with variable length columns ?
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Jun 24, 2011
Below query is taking a long time...
select gam.SOL_ID,COUNT(gam.FORACID) from gam,smt where
gam.ACID=smt.ACID and gam.ACID NOT IN(select ACID from imt) and
gam.SCHM_TYPE in('SBA','CCA','CAA','ODA') and GAM.ACCT_CLS_FLG='N' and
gam.SOL_ID IN(select SOL_ID from IMT) group by gam.SOL_ID
/
attached is the explain plan.
in which index on IMT table is not used. And the query is doing a FTS on IMT table. What needs to be done to avoid FTS on IMT table.
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Jun 28, 2010
What are the factors that decide on which column we should partition the table and which partition method we should chose.
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