A database structure that can improve the speed of queries at the cost of disk space and slower inserts/updates. It stores a copy of one or more columns but structures the data differently to allow for faster access.

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6
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1answer
200 views

Composite or Single-Field Clustering Key

My DBA and I are having a disagreement on index structure. Consider data for a medical claim... We have the Header table with fields like: ClaimId (varchar(50)), PaidAmount, MemberID... and for ...
6
votes
2answers
203 views

How the indexes are managed?

I am trying to understand how the indexes are managed for below common data types: 1- Numeric (Integer, Decimals) 2- String (Varchar, Char) 3- DateTime I have few questions: 1- How the indexes are ...
2
votes
1answer
615 views

SQL Server 2008 - Return records in chronological order, given a separation factor

This question was originally posted here http://stackoverflow.com/questions/8492149/return-records-in-chronological-order-given-a-separation-factor and re-posted on this forum given a user's advice. ...
5
votes
3answers
136 views

Dynamic temporary index creation

In my undergrad databases course, my professor mentioned that some DBMS software is so advanced that it can detect when a long-running query would benefit from an index. The DBMS can then create that ...
2
votes
3answers
976 views

Column sort order in CREATE INDEX statement?

When creating an index one can determine if an index column is sorted using ascending or descending order. BOL says that [ ASC | DESC ] Determines the ascending or descending sort direction for the ...
7
votes
2answers
8k views

How to promote an existing index to primary key in PostgreSQL

I know how to make a primary key within a table, but how do I make an existing index a primary key? I'm trying to copy an existing table from one database to another. When I show the table, the index ...
2
votes
0answers
255 views

MS-SQL index not using all the available columns as seek predicates

I have a sql query on a large table (>17 million rows) that some times does not populate all the predicates before performing index seek, which results in not filtering out enough rows and slowing the ...
2
votes
2answers
4k views

FoxPro DBF Index Corruption

We are running a pretty popular application in Russia and other CIS countries through a pretty old accounting system called BEST. It's all built on FoxPro (not Visual Foxpro) DBF/CDX tables. It's open ...
2
votes
2answers
349 views

How do redundant indexes impact query performance?

The indexes are affecting the ADD/UPDATE operations however I was wondering whether the redundant indexes will affect the SELECT query performance or not? How the redundant indexes are handled by ...
1
vote
1answer
941 views

How to create an UTC index from a 'DATE' typed column with Oracle?

I have a Oracle database with columns of type 'DATE' which store timestamps in local time zone. I need to query this column with timestamps in UTC timezone. How do I create an index on the column ...
1
vote
1answer
902 views

PostgreSQL 8.4 hangs on create table, reindex

I have a rather small database(200Mb) which was running on ubuntu 10.10/amazon ec2 fine for a year almost but today I ran into the following problem: When I create a table that references other table ...
2
votes
2answers
5k views

WITH using INDEX hint in Oracle

I have a fairly complicated query. I have written two different query to accomplish my goal. First one is using WITH, other one is using global temporary tables. First One: WITH A ( KNO .. ) , ...
6
votes
1answer
458 views

Permission to create Spatial Index

Permissions required to create a Spatial Index on a table, for this BOL says: Requires ALTER permission on the table or view. User must be a member of the sysadmin fixed server role or the ...
6
votes
1answer
563 views

Will a clustered index improve performance of updates performed sequentially on that clustered index?

I know indexes reduce data modification performance, but I have a task where (almost) all updates are done on items in a sequential order. Would a clustered index improve or reduce performance in ...
1
vote
1answer
294 views

Design Tagging module in the database

I've a database system which we want to define tags for many tables into it. For example I've videos, photos, ... different entities that we wish to make them taggable. The tags could be anything. By ...
5
votes
1answer
1k views

What is Sql Server Clustered Index in Oracle terminology

A clustered index in sql server like a dictionary or telephone directory. A,B,C,D it goes on. If you look up with a name Ozgur you start O then z etc. I would like a simple explaination for this ...
11
votes
4answers
465 views

Determining that Indexes on a table are unused

I’ve been running this script to try to find extraneous indexes select o.name as TableName, i.name as IndexName, p.reserved_page_count * 8.0 / 1024 as SpaceInMB, s.* from ...
6
votes
5answers
561 views

Are these good indexing guidelines?

I use indexes regularly but it's still hard for me in certain conditions to know if they are helping or hurting. There are a few guidelines I follow, but I am not sure if they are good nor am I sure ...
5
votes
1answer
546 views

Tuning queries and indexes using index analysis tool

I've been pointed to this script from several places which apparently helps with designing indexes in Microsoft SQL Server: http://indexanalysis.codeplex.com/ The problem is I'm using Sybase ASA 11, ...
1
vote
1answer
838 views

Does composite cluster index affect performance of seek/scan non-cluster index which is part of the composite?

I have bank transaction table with columns Division Brcode TrDate ProjectCode Accountnumber EffectiveDate DrCr Amount EndBalance In the other table the Brcode itself is unique and is assigned under ...
4
votes
2answers
1k views

How can an identity primary key index become fragmented?

From what I understand about index fragmentation, this should not be possible. The cases I have found in my databases are non-clustered. Example: ALTER TABLE [dbo].[ClaimLineInstitutional] ADD ...
2
votes
2answers
1k views

Rebuilding Index - sort in temp db

What is the significance of SORT_IN_TEMPDB when working with indexes on a table of significant size (20GB plus)? Where else does sorting take place?
1
vote
1answer
722 views

How to prevent big performance impact during index creation

I have an existing database that is missing some indexes. When I tried creating some the database server really suffered in CPU usage during index creation interfering with the regular workload. Is ...
3
votes
2answers
948 views

Is there any index with O(1) complexity for lookup in PostgreSQL?

Is there any index type in PostgreSQL that gives O(1) complexity for lookups? on strings?
6
votes
1answer
1k views

Using FORCE INDEX

I was in a presentation recently given by a Facebook MySQL engineer and he mentioned there that using FORCE INDEX reduces I/O. It was something to do with the MySQL Query Optimizer not needing to go ...
2
votes
2answers
204 views

In MySQL, should I add an index even if the query that scans the table is only ran once a month?

Concretely, is it worth it to add an index to a query that scans the table of a mysql database, even if that index would only be used once a month? For example, having a users a table and then ...
14
votes
5answers
505 views

Indexing from start or when performance problem arises?

My question is regarding use of indexes. Should I start indexing right from the start or when performance problem arises? We can also create temporary index while executing a query. What are the ...
2
votes
2answers
177 views

How to index this table (a_level, b_level, item_id)

I have a table of items, each of it has an a_level, b_level, and an item_id. Any b_level is dedicated to only one a_level (example: b_level 14 is "child" of a_level 2 only) Lets say we have million ...
11
votes
3answers
324 views

Included Column versus Filtered Index

We currently work with table named tb_tranfers. This table has 40 million rows and is ~26 GB in size (11 GB data, 15 GB indexes). 10 to 15% of the rows are soft-deleted rows (DeletedDate is not ...
0
votes
1answer
377 views

How SQLite index ID (or line number)

SQLite is based on a flatfile, and store virtual tables in a flatfile (I think based on offset, correct me if I'm wrong). But how it index the Primary Key (ID), which I think is identical to line ...
3
votes
2answers
2k views

How does Oracle handle composite index lookups?

MySQL cannot use a composite index in a lookup in which the WHERE condition doesn't include the columns forming a left-most prefix: MySQL cannot use the index to perform lookups if the columns do ...
2
votes
4answers
3k views

What impact do indexes have on the performance of table modifications? [duplicate]

I have always wondered what the effect indexes have on table modification in SQL Server. Will modification of a table will be slower with an increased number of indexes applied to that table? My gut ...
36
votes
5answers
12k views

Working of indexes in PostgreSQL

I have a couple of questions regarding working of indexes in PostgreSQL. I have a Friends table with the following index: Friends ( user_id1 ,user_id2) user_id1 and user_id2 are foreign keys to ...
13
votes
3answers
18k views

What is the default order of records for a SELECT statement in MySQL?

Suppose you have the following table and data: create table t(k int, v int,index k(k)) engine=memory; insert into t values(10, 1), (10, 2), (10, 3); When issuing select * from t where k = 10 with ...
10
votes
3answers
10k views

Best of MyISAM and InnoDB

Is it possible to make InnoDB to use indexes same as MyISAM instead of clustered index due to limitation of RAM while getting benefit of its concurrency performance?
4
votes
1answer
210 views

Strictly only RAM matters?

I have to work on a project which would have a extra large table with billions of records but only two fields one is id and another is text. And id would be set to BIGINT and PK then if 8+2 (extra 2 ...
3
votes
3answers
3k views

When do hash indexes become reasonable?

MySQL natively doesn't support hash indexes. So, making a pseudo hash column and creating an index on a hash column needs some thinking. And it seems to be widely understood that if the text field is ...
2
votes
2answers
458 views

What does “GIN doesn't support full index scans” mean?

I'm a RDBMS newbie and I have a PostgreSQL database of more than 50 millions lines, growing everyday. There is a column 'text', which contains human-generated text of around 20 words. I need to be ...
7
votes
2answers
274 views

Why is Oracle using the index here?

Name Null Type -------- -------- --------- ID NOT NULL NUMBER(4) GROUP_ID NUMBER(4) TEXT CLOB There is a btree index on group_id. Here's how many ...
2
votes
2answers
339 views

Indexing of Data Warehouse tables?

Maybe I have misunderstood something but I can recall reading an article which said that there is no reason to create non-clustered indexes on very large data warehousing tables? That is because ...
16
votes
2answers
8k views

How to know when/if I have too many indexes?

Running Microsoft SQL Server Profiler every now and then, it suggests me with a bunch of new indexes and statistics to create ("...97% estimated improvement..."). From my understanding every added ...
2
votes
1answer
177 views

What are hypothetical indexes?

They seem to be created by tools like DTA. For practical purposes they could be deleted, ignored or chosen to be created, but until then, they have no direct influence on the database.
29
votes
3answers
24k views

Why is my database still fragmented after I rebuilt and reindexed everything?

I have a database which I tried to defragment all the tables at once by running this T-SQL: SELECT 'ALTER INDEX all ON ' + name + ' REORGANIZE;' + CHAR(10) + 'ALTER INDEX all ON ' + ...
1
vote
1answer
132 views

Reasons against using local indexes

For Oracle 10g and above: except in cases where a local index cannot be used and a global index is needed (e.g. unique constraint), is there any reason to favor a global index over a local index?
5
votes
3answers
2k views

Indexing - Uniqueidentifier Foreign Key or Intermediary mapping table?

Looking for some expert views on this guys - I'm not a DBA by trade so would appreciate any advice. Comments on the rest of the schema aren't required as it is purely fabricated to illustrate my ...
2
votes
1answer
5k views

What I can do to speed up Key Lookup in my Query

I am using SQL2005 and against them I calling query simila to this declare @art table (id int primary key, naziv varchar(35) null, sifra varchar(15) null, jm int null); insert ...
2
votes
2answers
557 views

Full Name search query

We currently have a solution for this in production, but it's pretty bad. I'd like a fresh perspective on it please. We have a PERSON table with an ID, LAST_NAME, FIRST_NAME, MIDDLE_NAME, and ...
0
votes
2answers
584 views

FBI on function with concatenated string

I have an index in place (from days of old) that I'm curious about. It's on a basic person table and the function is upper("LAST_NAME"||','||"FIRST_NAME"||"MIDDLE_NAME"||"SUFFIX_NAME") When trying ...
5
votes
3answers
287 views

When you select from a table on an indexed column and order by that column in the opposite direction of the index, does the index help

Let's say I have a large table of transactions with a date field and an index on that field in ascending order. If I select that field from the table and order by in reverse order is it able to ...
4
votes
1answer
2k views

SQL Server 2008 R2 reindex job reorganise getting stuck

I am currently experiencing this job getting stuck in my nightly maintenance solution - ALTER INDEX [PK_ThirdPartySettleCalled] ON [evo_archive].[dbo].[ThirdPartySettleCalled] REORGANIZE WITH ...