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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Improve performance of COUNT/GROUP-BY in large PostgresSQL table?

I am running PostgresSQL 9.2 and have a 12 column relation with about 6,700,000 rows. It contains nodes in a 3D space, each one referencing a user (who created it). To query which user has created how ...
8
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2answers
217 views

Are columns which are not indexes, sorted on disk together with index?

Are columns which are not indexes, sorted on disk together with index, in MySQL, in MyISAM and InnoDB? An incorrect thought that I started to write: I think that probably not, since they are not ...
8
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1answer
2k views

Unexpected Seq Scan when doing query against boolean with value NULL

I have a database column called auto_review where column type is boolean. There is an index for that field, created using the ActiveRecord ORM. CREATE INDEX index_table_on_auto_renew ON table USING ...
8
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2answers
204 views

Non-Clustered Indexes - keys and nonkeys

I just want to make sure I'm on the right track with these concepts, so any feedback would be greatly appreciated. Here's my theory from the query I've just optimised, through a process of trial and ...
8
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2answers
650 views

How should I index a UUID in Postgres?

I'm new to PostgreSQL and somewhat new to databases in general. Is there an established way of how we should index UUID values in Postgres? I'm split between using hashing and using a trie, unless ...
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2answers
774 views

Clustered indexing is now must - why?

Earlier, there were non-conclusive to me debates / discussions on whether to (always) engage / avoid clustered indexes. Well, I understood that they are to be used sometimes with proper + specific ...
8
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3answers
314 views

Index tuning question

I am tuning some indexes and seeing some issues would like to take your advice On 1 table there are 3 indexes dbo.Address.IX_Address_ProfileId [1 KEY] ProfileId {int 4} Reads: 0 Writes:10,519 ...
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2answers
2k views

Slow ORDER BY with LIMIT

I have this query: SELECT * FROM location WHERE to_tsvector('simple',unaccent2("city")) @@ to_tsquery('simple',unaccent2('wroclaw')) order by displaycount I'm happy with it: "Sort ...
8
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2answers
194 views

What is the effect of replacing indexes with filtered (non-null value) indexes?

Our project runs a very large, very complicated database. So about a month ago, we noticed that the space used by indexed columns containing null values was getting too large. As a response to that, I ...
8
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1answer
5k views

PostgreSQL: COUNT(*) uses a sequential scan, not index

Why does PostgreSQL sequentially scans the table for COUNT(*) query, while there is a very small and indexed primary key?
8
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1answer
7k views

Need for indexes on foreign keys

I'm struggling with indexes, primary keys and foreign keys... And the need of having them all. If I have two tables, both of them have an integer as a primary key. The first table references ...
8
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1answer
89 views

How to reclaim space taken by an index that partially built and was terminated by a power outage

I'm running postgres (postgis) 9.4.2 on a mac (10.10.4). I've got a couple big tables (several TBs). During an index build on one of them that takes about a week, I watched the available HD space ...
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2answers
2k 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, ...
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1answer
8k views

MySQL INNODB corruption after server crash during concurrent truncate command

My server crashed today I think due to a concurrent truncate table command on one of our INNODB tables. The server could be restarted, but after it starts up, everytime I try to issue an SQL command, ...
8
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1answer
326 views

Why would function based indices I’ve created lower the cost but not show up in the explain plan breakdown?

Sorry for the terrible column/table names but since this is for a work project I wanted to insure it was OK to ask. I was just hoping to at least learn why I'm not seeing my functional indices being ...
8
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2answers
156 views

Which to trust?

We are troubleshooting a long-running issue with a vendor. Their software has a tendency to freeze up and stop working once or twice a week causing major disruptions to our operation. They have been ...
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4answers
16k views

When to add indexes to #temp tables?

When testing stored procedures in SSMS, it sometimes says there is a missing index on #someTempTable____________________000000000000005B] (someField) etc etc When I do add them like this to the sp: ...
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2answers
1k views

Custom unique column constraint, only enforced if one column has a specific value

Is it possible to have a custom unique column constraint as follows? Suppose I have two cols, subset and type, both strings (though the data types probably doesn't matter). If type is "true", then ...
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5answers
6k views

Improve sort performance in PostgreSQL?

I've got a simple blog database in postgres-8.4 which has two tables, articles and comments. I have a query (generated by Django) that wants to get the latest article of type 'NEWS' and also find the ...
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3answers
1k views

Multidimensional indices in databases

Which databases use real multidimensional indices? Is oracle ever using several indices to get data from tables, or will it always take the one that seems to have the highest selectivity? How about ...
7
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2answers
292 views

Should I mark a composite index as unique if it contains the primary key?

Given some table with a primary key, e.g.: CREATE TABLE Customers ( CustomerID int NOT NULL PRIMARY KEY, FirstName nvarchar(50), LastName nvarchar(50), Address nvarchar(200), Email ...
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4answers
433 views

how to explain indexes

This question is about teaching: When I learned databases, we talked about indexes being like the card catalog in the town library. We had at least an author index, a title index, then the Dewey ...
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3answers
3k views

Query performance degrades with time and use

I have been fighting a problem for several weeks now where the performance of my SQL Server queries degrade over a few days of use. In addition every few days, a query will simply not return from my ...
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2answers
4k views

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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1answer
346 views

Composite Primary Key in multi-tenant SQL Server database

I'm building a multi-tenant app (single database, single schema) using ASP Web API, Entity Framework, and SQL Server/Azure database. This app will be used by 1000-5000 customers. All the tables will ...
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1answer
1k views

How to set SQL Server index pages per fragment?

I have SQL Server 2008, and a number of databases. I have discovered that one of my table's indexes is extremely fragmented (How I know: http://msdn.microsoft.com/en-us/library/ms189858.aspx) The ...
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3answers
1k views

Creating an index in both asc and desc directions

Over the past few weeks I've been raging against an old Firebird database. This database is crappy for all sorts of reasons, but one thing I noticed was that every single field of every single table ...
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3answers
501 views

Best practices for change management with indexes

Our IT shop is first starting to build a group of DBA's. All of us (myself included) have come over from the application development/architecture world, so the DBA world is still fairly new to us. ...
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2answers
9k 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 ...
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6answers
917 views

Fast reads without paying the price on writes

We have a large append-only table containing financial transactions. On average 1000 transactions are inserted per minute. Since there are now more and more usecases where we actually want to read, ...
7
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1answer
263 views

Query optimizer recommends adding index instead of using existing index

I am trying to determine why the query optimizer in SQL Server is recommending creating a new index instead of using an existing index that appears to be sufficient for the query. First the table. ...
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2answers
2k views

Defragmentation - Rebuilding Indexes SQL Server 2005

I'm researching defragmenting databases and it seems the following SQL statement is what I'm looking for: ALTER INDEX ALL ON mytablename REBUILD WITH(ONLINE = ON) When I pull the info from ...
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3answers
984 views

Should I separate frequently updated columns?

I have a users table that contains users' information and a column named credits that is frequently updated. On index page I'm showing list of users with basic user information but I don't need ...
7
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1answer
179 views

Ola Hallengren Index Script not Reindexing

First, I realize a similar question was asked and the poster had page count set to 1000 for a 679 page index; not what's going on. I have Ola's script set as @Databases nvarchar(max) ...
7
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3answers
167 views

Can PostgreSQL use nulls in its indexes?

I've been reading this book which says that The database assumes that Indexed_Col IS NOT NULL covers too large a range to be useful, so the database will not drive to an index from this ...
7
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2answers
6k 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 ...
7
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1answer
103 views

Index SEEK is not used unless OPTION (RECOMPILE)?

(Question moved from SO) I have a table (dummy data) with clustered index contains 2 columns : Now I run those two queries : declare @productid int =1 , @priceid int = 1 SELECT ...
7
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1answer
124 views

Will a Full-Text Catalog with Track changes: AUTO automatically update if Change Tracking for that table is not enabled?

I have this database table that is suppose to keep the full-text index up-to-date. However I am not seeing it happening at all (no error in the log because the last log I see was when I triggered it ...
7
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2answers
301 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 ...
7
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1answer
1k views

Index usage stats DMV indicates no index activity

I'm trying to obtain information on indexes. According to several websites, the below TSQL query should join information on indexes to the indexes table, returning indexes and related information. ...
7
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1answer
1k views

Indexed view not being used - SQL Server [duplicate]

I've a query with multiple joins which takes long time to return data for one date. I've created an indexed view on the same. I set all the required options appropriately, while creating view and ...
7
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1answer
4k views

Why not rebuild indexes with page count <1000?

I use Ola Hallengrens script for Index maintenance. Before I did that, I used the following query to see which indexes are fragmented most: SELECT dbschemas.[name] as 'Schema', dbtables.[name] as ...
7
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1answer
11k views

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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2answers
276 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 ...
7
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1answer
194 views

Which is more efficient b+ tree or search (binary or linear)?

SELECT A FROM T WHERE M > 1000 AND M < 5000; I am unable to judge which of the below is best suited for the above query: Linear search Binary search on M B+-tree with index on M B+-tree with ...
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2answers
1k views

Finding the query causing the missing index DMVs

How can I find the query causing the missing index DMVs suggesting to create a particular index? Thank you.
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3answers
3k views

Dropping Hypothetical Indexes

In the past I thought I'd deleted hypothetical indexes using either a DROP INDEX statement for clustered indexes and DROP STATISTICS statement for non-clustered indexes. I have a database that is ...
7
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1answer
790 views

B-tree node split strategy in SQL Server for monotonically increasing value

Consider a B-tree index on a value that will always increase monotonically, e.g. a column of type IDENTITY. With a conventional B-tree implementation, whenever a node is full, it will be split 50%/50% ...
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1answer
5k views

MySQL Hanging Completely when `ALTER TABLE… ENABLE KEYS`

I know very little about database administration but I have to deal with some very large tables on my site. This server has 64GB of RAM and Intel Core i7-3820 (4 x 3600 MHz). Most of everything it ...
7
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1answer
879 views

computed columns, index, clustered index and covering index?

We all know the we can only have one clustered view per table, cool. But apparently you don't have values of computed columns on leaf even when using a clustered index and they are computed each time. ...