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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Interpreting an execution plan

I need some help analysing some simple t-sql execution plans. I have a table [User] with the following 3 columns: Id(Primary Key), Username(nvarchar(50)), FirstName(nvarchar(50)) I have Created an ...
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4k views

How to check for existence of an INDEX on a column independent of used SQL database

Is there are unified way of how to check for the existance of an INDEX for a given column irregardless of the actual SQL database system used? For MySQL one could for instance check for the existance ...
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699 views

Don't rebuild indexes < 1000 pages - then why bother having them?

Microsoft recommends not bothering to rebuild indexes that have less than 1,000 pages (from memory I think it's because they are so small that they will be held in RAM). If I'm not rebuilding them, ...
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2answers
3k views

Should I refresh query plan cache

Please let me explain my problem and situation: I have a web application - MVC3, MSSQL Server 2005, LinqToSQL. It has been running great until one fine morning I pushed a lot of rows to a table that ...
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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 ...
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874 views

How can I force MySQL to IGNORE ALL indexes?

I have read articles about FORCE index, but how can I force MySQL to IGNORE ALL indexes? I tried SELECT * FROM tbl IGNORE INDEX(*), but I was not successful. As for why I (and others) need to do ...
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Index on primary key not used in simple join

I have the following table and index definitions: CREATE TABLE munkalap ( munkalap_id serial PRIMARY KEY, ... ); CREATE TABLE munkalap_lepes ( munkalap_lepes_id serial PRIMARY KEY, ...
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421 views

Why index is not used with order by?

I trying to get info about why MySQL does not using my index when I create a inner join and trying to ORDER BY on the end. I have my SQL query here: SELECT * FROM product p INNER ...
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1answer
830 views

Does MySQL still handle indexes in this way?

Dropping a duplicate index in MySQL was taking rather long, so while I was waiting I searched about it & found this post from 2006, talking about how MySQL handles ADD and DROP index. If a ...
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137 views

Confused about why a particular index is being used

I have a table (with 170M rows) that looks as follows: CREATE TABLE [dbo].[Panel] ( [SubId] [varchar](15) NOT NULL, [LineageId] [int] NULL, [Buck] [varchar](20) NULL, [Lot] ...
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How to create an index on an integer json property in postgres

I can't figure out for the life of me how to create an index on a property of my json column which is an integer. I tried it this way (and also dozens of others) CREATE INDEX user_reputation_idx ON ...
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652 views

If I update a column record in a table, will indexes that do NOT have this column in it be affected?

In terms of performance if I have a table like so: CREATE TABLE [TESTDATA].[TableA]( [Col1] [nchar](5) NOT NULL, [Col2] [nchar](2) NULL, [Col3] [float] NULL CONSTRAINT [TableA_PK] PRIMARY ...
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156 views

Are existing entries immediately included into a newly created index?

Suppose I have a table Stuff with a column City and no indices including that column. I populate the table. Then I decide to create an index: CREATE INDEX [StuffOnCityIndex] ON [dbo].[Stuff](City ...
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288 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 ...
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How are multiple indexes used in a query by MySQL?

Imagine a table where there are separate indexes on columns a and b. The query runs somewhat like this: SELECT col1, col2 FROM <table> WHERE a = 'value_1 AND b = 'value_2'; Now, does this ...
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498 views

How to make this query use my multicolumn index?

Currently, I have a view which is defined like this: View "public.customer_list" Column | Type | Modifiers | Storage | Description ...
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153 views

Is it possible to get seek based parallel plan for distinct/group by?

An example from this question shows that SQL Server will choose a full index scan to solve a query like this: select distinct [typeName] from [types] Where [typeName] has a non-clustered, ...
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1answer
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What is a non-clustered index scan

I know what table scan, clustered index scan and index seek is but my google skills let me down to find a precise explanation into non clustered index scans. Why and when a query uses a non clustered ...
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Programmatically find indexes that cannot be rebuilt online

I am automating rebuild and reorganise indexes using T-SQL. I run into problems with indexes that cannot be rebuilt online. Primarily this happens because ntext/nvarchar columns are included. Is ...
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981 views

Should I rely on Database Engine Tuning Advisor for creating indexes?

How should I rely on Database Engine Tuning Advisor for creating indexes and statistics? I find more often than not, it generates overly complex indexes that (I think) would be more costly in index ...
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1answer
719 views

Index defrag takes forever to run

We have an Agent job that runs every morning at 2a.m. to defrag the top 5 biggest tables. Usually it takes around 20 mins to complete. It has stayed this way for several years. However, recently (last ...
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397 views

SELECT * WHERE VarCharColumn IN (…) Optimization

I have a list of 3000 strings, and I am passing them (twenty at a time) into a parametrized IN clause. It definitely isn't getting the results I would like to see ~ 500ms per execution. The column is ...
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New Index on table cause table to be locked really often

Here are my tables : CREATE TABLE [dbo].[Trackers] ( [IdTracker] INT IDENTITY (1, 1) NOT NULL, [IMEI] NVARCHAR (16) NULL, [CreationDate] ...
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1answer
387 views

How to disable or delete an index

I created a non-clustered index on a live server (SQL Server 2008 R2) and it turned out not to give the performance benefits that I was hoping for. So I want to delete the index again. Unfortunately ...
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159 views

Why is an entire index that is infrequently used stored in the buffer pool?

I have been looking at the memory usage of a server and noticed something odd when drilling into the details. One index is eating up ~15GB of the buffer pool. That happens to be the size of the entire ...
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5k views

Improve speed of index rebuild on SQL server

I'm importing a large amount of data into an empty database, and before I start I disabled all non-unique non-clustered indexes to see if I could improve the performance of the import. Now I want to ...
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Best value for fill factor in index

I use SQL Server 2008 R2 and want to set value for fill factor property in each index. I look for recipe to calculate best value for this property (have better performance when insert record) . Also ...
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1answer
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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 ...
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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 ...
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1answer
1k views

How to Index a JOIN result of two or more tables in order to improve the performance in SQL server?

I am new to indexing and gone through the basics of indexing. I can find a default clustered index for the primary key constraint within the indexes part of the corresponding table, but after creating ...
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MySQL: Index when joining to tables not being used (Performance optimizing question)

I need to optimize the following query: SELECT /* [things omitted] */ articles.blogpost_id, articles.id AS articleid FROM blogposts JOIN articles ON articles.blogpost_id = blogposts.id WHERE ...
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660 views

“Recheck Cond:” line in query plans with a bitmap index scan

This is a spin-off from comments to the previous question: Postgres 9.4.4 query takes forever Using PostgreSQL 9.4, there always seems to be a Recheck Cond: line after bitmap index scans in query ...
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SQL Server 2008R2 XML Column Index strategy for large tables?

I am working with SQL Server 2008 R2 and some XML columns in a very large table. I understand that I cannot use Selective XML Indexes due to our SQL Server version being < 2012. I'm brand spanking ...
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1answer
198 views

Slow fulltext search for terms with high occurence

I have a table that contains data that is extracted from text documents. The data is stored in a column called "CONTENT" for which I have created this index using GIN: CREATE INDEX ...
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Postgres is performing sequential scan instead of index scan

I have a table with about 10 million rows in it and an index on a date field. When I try and extract the unique values of the indexed field Postgres runs a sequential scan even though the result set ...
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864 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 ...
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1answer
126 views

SMS Suggesting covering all columns in an index?

I'm still a bit newer to indexes and database works, so I may very well be missing something obvious. SMS suggested adding a covered index to one of my tables that Indexes on the column I believe ...
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1answer
853 views

Database having only db_datareader shows invalid properties for a index

If a SQL server database user has only public permission in server roles and for a particular database only db_datareader and public permission then while trying script index as CREATE To option in ...
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Does UPDATE INDEXES work for local indexes?

I have two tables in Oracle 11.2. First is partitioned and has local index (non-prefixed): CREATE TABLE table1 (col1 INT, col2 INT) PARTITION BY LIST(col1) ( PARTITION p1 VALUES(1), PARTITION ...
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Dropping and recreating indexes for performance reasons?

I'm maintaining Somebody Else's Code. There's a stored procedure that's run once a day or week (depending on config), that migrates a bunch of records from an active table to an archive. But it's ...
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617 views

Optimizing IP Range Search?

I have a simple query and table, and I would like to know which indexing is efficient on this kind of table and query. In my table I have 3 columns CREATE TABLE mYTable(ipFrom BIGINT, ipto BIGINT, ...
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Monitoring Progress of Index Construction in PostgreSQL

Is there a way to monitor the progress of the creation of an index in PostgreSQL. I am creating an index on a large table and I would like to see how fast this is occurring. Is there a way to monitor ...
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1answer
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Estimating impact of indexes SQLite database size

I'm trying to estimate the database size (on disk) for a SQLite DB that includes a number of indexed columns. These columns are of (SQLite) type Integer and String. It's straightforward enough to ...
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2answers
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looking for missing indexes in the cached execution plans

I have the following query that shows me what is cached in sql server: SELECT cp.objtype AS ObjectType, OBJECT_NAME(st.objectid,st.dbid) AS ObjectName, cp.usecounts AS ExecutionCount, st.TEXT AS ...
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1answer
157 views

Managing and speeding up queries on PostgreSQL table with over 3 trillion rows

I have time series data which spans over 10 years and has over 3 trillion rows and 10 columns. At the moment I use a PCIe SSD with 128GB of RAM and I am finding that querying takes a significant ...
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1answer
194 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? ...
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789 views

Should I use a composite or single-column index?

I have the following columns in my database table (Medicines). ID bigint, MedicineName nvarchar(50), BrandName nvarchar(50), MedicineCode nvarchar(20), and price,quantity. I am making a stored ...
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1answer
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Why does CREATE INDEX … WITH ONLINE=ON block access to the table over a period of minutes?

I have an existing table: CREATE TABLE dbo.ProofDetails ( ProofDetailsID int NOT NULL CONSTRAINT PK_ProofDetails PRIMARY KEY CLUSTERED IDENTITY(1,1), ProofID int NULL, ...
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1answer
397 views

RESOURCE_SEMAPHORE_QUERY_COMPILER waits in Microsoft SQL Server 2008 Enterprise

Could fragmented indexes on Microsoft SQL Server 2008 Enterprise cause RESOURCE_SEMAPHORE_QUERY_COMPILER waits? The last two weeks one of our applications has had downtime due to ...
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Algorithmic order of table indexes for table operations

I have not been able to find a clear indication of the impact table indexes have on the algorithmic order of table operations. I am not interested in the nuts & bolts of specific implementations; ...