The process of determining which indexes are useful and which are not.

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23
votes
2answers
7k views

Is a composite index also good for queries on the first field?

Let's say I have a table with fields A and B. I make regular queries on A+B, so I created a composite index on (A,B). Would queries on only A also be fully optimized by the composite index? ...
18
votes
2answers
9k views

Does a re-index update statistics?

I've been doing the MS10775A course this past week and one question that came up that the trainer couldn't answer reliably is: Does a re-index update the statistics? We found discussions online ...
15
votes
1answer
7k views

Should I use many single field indexes, instead of specific multi column indexes?

This question is about the effectiveness of a SQL Server indexing technique. I think it is known as "index intersection". I'm working with an existing SQL Server (2008) application that has a number ...
15
votes
4answers
2k views

effective mysql table/index design for 35 million rows+ table, with 200+ corresponding columns (double), any combination of which may be queried

I am looking for advice on table/index design for the following situation: I have a large table (stock price history data, InnoDB, 35 million rows and growing) with a compound primary key (assetid ...
13
votes
2answers
6k 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 ...
10
votes
3answers
195 views

One index or two?

I have the following index created on a table in my database: CREATE INDEX [idx_index1] on [table1] (col1, col2, col3) The server is suggesting the following 'missing' index: CREATE INDEX ...
9
votes
1answer
435 views

Poor query performance

We have a large (10,000+ lines) procedure that typically runs in 0.5-6.0 seconds depending on how much data it has to work with. Over the past month or so it has started taking 30+ seconds after we do ...
8
votes
2answers
2k views

PostgreSQL Index Caching

I'm having difficulty finding 'lay' explanations of how indexes are cached in PostgreSQL, so I'd like a reality check on any or all of these assumptions: PostgreSQL indexes, like rows, live on disk ...
8
votes
4answers
467 views

What are the performance considerations between using a broad PK vs a separate synthetic key and UQ?

I have several tables where records can be uniquely identified with several broad business fields. In the past, I've used these fields as a PK, with these benefits in mind: Simplicity; there are no ...
7
votes
4answers
2k views

How will large index INCLUDE fields effect system performance?

This question is about SQL Server index performance with a varchar(2000) as an INCLUDE in a covering index. I’m trying to improve performance in an slow and unstable database application. In some ...
7
votes
1answer
1k views

What factors go into an Indexed View's Clustered Index being selected?

Breifly What factors go into they query optimizer's selection of an indexed view's index? For me, indexed views seem to defy what I understand about how the Optimizer picks indexes. I've seen this ...
7
votes
2answers
1k views

Filtering data ordered by rowversion

I have a SQL table of data with the following structure : CREATE TABLE Data( Id uniqueidentifier NOT NULL, Date datetime NOT NULL, Value decimal(20, 10) NULL, RV timestamp NOT NULL, ...
6
votes
2answers
304 views

How to optimize NOT IN statement

Why does NOT IN performs INDEX SCAN instead of INDEX SEEK? Here's my current index on the table, CREATE NONCLUSTERED INDEX [idx_dmcasarms_CourseList_cDesc] ON [dbo].[courselist] ( [c_desc] ...
6
votes
2answers
4k views

Multicolumn index and performance

I have a table with a multicolumn index, and I have doubts about the proper sorting of the indexes to get the maximum performance on the queries. The scenario: PostgreSQL 8.4, table with about 1MM ...
6
votes
2answers
2k views

Viable strategies for rebuilding indexes online in SQL Server 2008 R2 Standard edition?

We use SQL Server 2008 R2 Standard edition (we can't afford Enterprise edition on all our production database servers) and have to periodically maintain the critical indexes (rebuilding/reorganizing) ...
6
votes
1answer
207 views

Is there any reason to use index for very small tables (up to 1000 rows)?

During application development I have a lot of tables that store "small" amount of data (usually 10-40 values, id + value and sometimes type) which hold attributes for "objects", like fresh/rotten, ...
6
votes
2answers
820 views

Adding a Clustered index to a HEAP table on someone else's app

We're using a proprietary application based on SQL Server 2005, which has many HEAP based tables (that is, no Clustered index). Over the years, these tables have grown badly fragmented (e.g. 99% ...
6
votes
2answers
5k views

How can I improve the speed of a query on a 20 million+ row table?

I have a query that is used for getting internet traffic statistics of certain IP addresses. There are separate IP address fields for hosts and blocks of IPs called assignments. The data is stored ...
6
votes
2answers
5k views

What is the difference between ALTER INDEX and DBCC DBREINDEX?

Is the only difference between ALTER INDEX [index_name] on [object_name] REBUILD with (ONLINE=OFF, FILLFACTOR=90) and DBCC DBREINDEX([dbname], 90) just that the DBCC command will reindex all ...
6
votes
1answer
414 views

Why is multiple independent index always better than concatenated index [closed]

Index Merge: Combining Multiple Indexes It is one of the most common question about indexing: is it better to have one index for each column or a single index for all columns of a where ...
6
votes
2answers
165 views

Index that is not used, yet influences query

I've got a PostgreSQL 9.3 table with some numbers and some additional data: CREATE TABLE mytable ( myid BIGINT, somedata BYTEA ) This table currently has about 10M records and takes 1GB of ...
5
votes
3answers
4k views

Indexing a PK GUID in SQL Server 2012

My developers have setup their application to use GUID's as PK for pretty much all of their tables and by default SQL Server has setup the clustered index on these PK's. The system is relatively ...
5
votes
2answers
388 views

How to design index for faster deletes

I want to speed up following piece of code delete from ssn_sdo where (art_id=@art_id and skl_id=@skl_id and @level=0 ) or (art_id=@art_id and skl_id=@skl_id and @level=1 and ...
5
votes
2answers
224 views

Indexing a large static dataset

My current situation is this: I have 328 million lines of data in a flat csv file. Not optimal. I want to be able to query this data (I'll explain in more detail). Grep is getting tired. This data is ...
5
votes
1answer
491 views

How can a fill factor of 0 or 100 be the same?

As of my understanding, Fill factor of 80 implies that 20 percentage of each leaf-level page will be empty to enable future growth. I can't correlate how fill factor of 0 and 100 can be the same! Am I ...
5
votes
2answers
1k views

Finding stored procedures with missing indexes

How to scan for stored proc that need indexes to be created. Anyone have any idea? Basically we have stored procedures that run very slowly. I'm wondering if there is some kind of automated script ...
5
votes
2answers
2k views

Cardinality rule for bitmap indexes

The Oracle documentation includes the following advice: A bitmap index should be built on each of the foreign key columns of the fact table or tables In that reference, there is even a bitmap ...
5
votes
1answer
173 views

Sudden poor SELECT performance on a large table with existing indexes

My company uses a software suite in which the only thing I can truly modify is the database. We've always had performance issues (mostly hardware problems that we hope to resolve soon), but lately ...
5
votes
3answers
2k views

SQL server indexing foreign keys, covering indexes included columns

I have pulled a list of FK's that do not have indexes on them. If a FK does not have a dedicated index on them but are part of wider indexes used for covering queries, Should they have a dedicated ...
5
votes
2answers
495 views

Any advantage of having a second index with included columns on a primary key?

I'm reviewing our database and noticed that on a particular table we have the following indexes: Table: Col1 INT IDENTITY(1,1) Primary Key Col2 INT ... about 15 more columns .... ColN ...
5
votes
2answers
230 views

how to increase speed of this mysql query?

How I can increase speed of this search query? This search bring news based on time and title and text. each item has own factor. SELECT * , MATCH (`title`) AGAINST ('tax in work') * 1.65 AS ...
5
votes
1answer
180 views

PostgreSQL operator uses index but underlying function does not

I'm attempting to use JSONB with JDBC, which means that I have to avoid any of the operators which use the '?' character (as the PostgreSQL JDBC driver has no escaping for this character). Taking a ...
5
votes
2answers
190 views

Indexing strategy for dynamic predicate

Assume SQL Server 2012 Standard edition. My database has a table with 500 million rows. The table has about a dozen columns, none of which are very wide (some varchar(100)'s and some ints). The ...
5
votes
1answer
655 views

SQL Server 2008 Maintenance Plan Failure

Instead of using my old school index rebuild script I had decided to use 2008's built-in Maintenance Plan to do a simple Rebuild Index task. The details are: Connection = Local server connection ...
4
votes
2answers
1k views

How do I know what indexes to create for a table

Is there a way I can figure out the best way to know which indexes to create for a table?
4
votes
3answers
2k views

Lookup table for a one-to-many relationship

I have a tickets table with an id that I need to associate to a lookup table where the counterpart of that data is another id that is controlled from an outside source. tickets - id - sutff lookup - ...
4
votes
1answer
114 views

What is the difference between these two index declarations and do I need both?

I was examining a script with 'Display Estimated Execution Plan' and it made several recommendations for indexes to add to the database. I added them and the script did indeed run much faster. Now ...
4
votes
3answers
366 views

Using DTA vs. evaluating DMVs?

Currently I am confronted with a production SQL Server database where someone had added almost all missing index proposals from DTA. Form How to determine if an Index is required or necessary I have ...
4
votes
2answers
100 views

StackExchange clone: where should I add my indexes?

I'm creating an open source stack exchange clone and the following is my schema. What should I add indexes on for it to be optimal? Here is the schema in Rails format (SQL format below as well): ...
4
votes
3answers
238 views

Most efficient (or meaningful) way to index grid-based data

I have a MySQL table which I expect to be in surplus of a few million rows and 99% select statements. The problem I am having is coming up with a meaningful way to determine the Primary Key. (I have ...
4
votes
1answer
2k views

What are the disadvantages if indexes are added on all columns?

I know, that it is not a good design to set too many indexes, but just for understanding the theory: What exactly are the disadvantages if you add an index on all columns in a table in MySQL? Are ...
4
votes
1answer
68 views

Does MySQL exectution plan depend on available indexes?

Does MySQL choose an execution plan for a given query taking into account what indexes are available, or does it first choose an execution plan and then uses indexes if they are available? ...
4
votes
1answer
183 views

Table with clustered Index consuming max memory causing low PLE alerts

For one of my server with below configuration i am continuously receiving alerts for low PLE which ranges between 20- 400 and an average of 90-100 in a day: Server: SQL server 2008R2 Databases : ...
4
votes
1answer
351 views

How to setup complex multi-column index for massive table

I've searched what I could search on Google, SO, etc and haven't found an answer that would seem to fit what I'm looking for. I'm hesitant to make a post about this as I'm sure the answer is out there ...
4
votes
1answer
134 views

Where to place non clustered index

Execution plan clearly showing that one of my table used in query is useing Clustered Index Scan. From this node, how can i guess that which columns should be part of my non clustered index key and ...
4
votes
1answer
464 views

Using indexes to create multiple relationships to a table in order to enforce data integrity and add meaning

I'm working on an inventory database that uses supertype/subtype model. My question regards creating multiple relationships with the same tables using the primary key and composite indexes that also ...
4
votes
2answers
5k views

Primary key vs. unique index: performance difference with foreign keys?

Will there be any difference in performance if you compare a query fetching data via a join between two tables where there's a relationship against either of the following: A primary key A unique ...
4
votes
2answers
635 views

Why is a secondary index chosen over a clustered index for SELECT COUNT(*) …?

In this query: select count(*) from largetable; a secondary index is chosen: mysql> explain select count(*) from largetable; ...
4
votes
1answer
131 views

Optimizing indexes

I just began optimizing my schemas with indexes (pretty late I guess). I never dealt with huge dataset but I'll be soon coping with about 1 to 5 millions rows. Here is the schema I'm using right now ...
4
votes
1answer
2k views

How to properly index hstore tags column to faster search for keys

I imported a large area of OpenStreetMap's planet.osm file into a postgresql database. The database contains a table called nodes. Each node has a geometry column called geom and a hstore column ...