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

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Improve performance of query with many joins

From the following explain plan: explain SELECT imei, cliente_avl_equipo.id_cliente AS idcliente, cliente_avl_vehiculo.grupo AS grupo, avl_vehiculo.id, ...
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Tuning read-intensive queries - Oracle

Now this might be very vague but Im sure I can provide more info on them.. my query is that is it recommended to use tablespaces if different block size because I have a table in which number of reads ...
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144 views

Why is the optimizer doing a table scan vs Index Seek

Probably a straight forward answer, but I'm too bleary eyed to see it. Have a simple query that is pulling the top 100 rows based on a char column. The column has an index on the where column. ...
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Does a covering nonclustered index help to answer Select * queries?

Our application developers run a lot of SELECT * queries against our database system, unfortunately. The missing index suggestions of sys.dm_db_missing_index contain a lot of cases that indicate to ...
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Reasons why plans of sys.dm_exec_cached_plans do not match actual plans?

I re-assess index / query optimization and actually focus on key/bookmark lookpus that could be eliminated. Using a script of Jonathan Kehayas I go through the list of query plans that used those ...
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1answer
47 views

How to make unique check without creating heavy index in postgres

I need to implement unique check for INSERT and UPDATE operations, but I would prefer to avoid creating heavy unique index (which is approx 12Gb now) on my table. Now I have unique partial index and ...
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25 views

Index comparison

On my Production server (SQL2008) I have a query that returns suggestions of indexes. SELECT * FROM sys.dm_db_missing_index_groups g INNER JOIN sys.dm_db_missing_index_group_stats gs on ...
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82 views

How to determine the best index on a table with 3 nullable columns?

I am examining a users table similar to this: CREATE TABLE `users` ( `id` int(11) NOT NULL AUTO_INCREMENT, `username` varchar(50) DEFAULT NULL, `email` varchar(255) DEFAULT NULL, `password` ...
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Why does SQL Server use this index?

I have two indexes on a table with 786602 rows: CREATE NONCLUSTERED INDEX [IX1] ON [dbo].[O] ([A] ASC, [B] ASC) INCLUDE ([c1], [c2], [c3]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, ...
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1answer
126 views

How to speed up queries in MySQL on a table with ~50 million rows

The table has 4 columns of type datetime, smallint(6), tinyint(4) and decimal(15,5). The first 3 columns are PK. There are four indexes on the table: one with all the PK columns, and one with each ...
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55 views

Why is this PostgreSQL query table scanning

I am running PostgreSQL 9.3. The database is of all of the medical NPIs (national provider numbers). I have created the following indexes: CREATE INDEX ...
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Combine several missing index suggestions with one index?

I investigate on missing indexes recommendations of my sql server engine. Looking at the most useful ones (for a specific table) that are candidates based on their potential usage and potential ...
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Minimum Oracle table size making IOT advisable?

I have inherited an IOT that doesn't seem to merit it because: only 25k rows fairly pure join table, non-index fields rarely queried total index width only ~125 bytes total row width only ~160 bytes ...
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2answers
190 views

MongoDB uses only one index on simple query with sorting

So the problem is that I'm having a huge collection and I'm trying to run a query that filters and sorts on only fields that have indexes on them. I have these two indexes: ...
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1answer
108 views

Create index clustered X NonClustered with include

I have a table like : create table x (a varchar(20), b varchar(30), c varchar(30), primary key clustered(a asc)) so I'm wondering if I create an index like: Create nonclustered index test on x(a) ...
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49 views

Missing indexes dmv count varies every day

I have a question to the missig index dmv. BOL says: Information returned by sys.dm_db_missing_index_details is updated when a query is optimized by the query optimizer, and is not persisted. ...
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51 views

MySQL Finding index size for compound unique indexes

I'm using following query to get index and data sizes for tables in database. But unfortunately it doesn't show index size for compound unique indexes. How can i get index sizes for compound unique ...
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155 views

Howto Identify Clustered Index Candidates

I find myself in a situation where I have inherited the db and people complain about database performance. I identified about a dozend of tables not having a clustered index or a not carefully planned ...
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DMV Index proposals still reported as missing

We have recently converted a big client running our patient/journal application from ORACLE to MSSQL, and after the conversion we have had quite a few performance issues. After running the DMV query: ...
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3answers
120 views

Performance of rare SELECT vs. frequent INSERT in timeseries data

I have a simple timeseries table movement_history ( data_id serial, item_id character varying (8), event_time timestamp without timezone, location_id character varying (7), ...
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3answers
101 views

What indexes should one use for this two-table setup?

I have the following two-table setup: CREATE TABLE relationships ( id bigint(20) NOT NULL AUTO_INCREMENT, type varchar(20) COLLATE utf8mb4_unicode_ci NOT NULL, PRIMARY KEY (id), ...
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1answer
69 views

MySQL Query causing high CPU and taking forever to execute

this below query takes a long time to execute in excess of 120 seconds, upon checking the explain plan it seems to be using using where, using temporary; using filesort. Since the application is a ...
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134 views

Function Based Index with XPATH extractValue

// Oracle Version 11.2.0.4 Standard Edition // OS RedHat I am trying to create a function index on a large table, based on using an XML object. So I have done stuff such as: CREATE INDEX ...
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Extremely slow query on indexed column

I'm getting a extremely slow query on an indexed column. Given the query SELECT * FROM orders WHERE shop_id = 3828 ORDER BY updated_at desc LIMIT 1 explain analyze returned: QUERY PLAN ...
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1answer
241 views

How to set up indexed view when SELECTing TOP 1 with ORDER BY from different tables

I am struggling to setup an indexed view in the following scenario so that the following query performs without two clustered index scans. Whenever I create an index view for this query and then use ...
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Wide clustered index vs multiple narrow nonclustered indexes?

Say I have a contrived Student table like so: CREATE TABLE Student ( Id IDENTITY INT, SchoolId INT NOT NULL, FirstName VARCHAR(20) NOT NULL, LastName VARCHAR(20) NOT NULL ) ...
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91 views

MongoDB Slow updates

My application is doing extremely slow updates, despite my query being covered by indexes. My query is: query = {'spot': df_youtube['spot'].values[key], 'segment': ...
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292 views

Script to find unused indexes over a period of time doesn't work in Oracle 11g

The statspack_unused_indexes.sql script described in this page would be incredibly useful to me, but it has been coded for an earlier version of Oracle. When I try to run it on 11g, I get the ...
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283 views

Slow query performance due to temporary file?

Here is the query: SELECT "products".* FROM "products" WHERE (status > 100) AND "products"."above_revenue_average" = 't' AND ("products"."category_id" NOT IN (5)) ORDER BY ...
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1answer
59 views

Index is seeked and scanned - is there a risk for seek to fail after modification?

I have an index that has been seeked 230.000 times and scanned 130.000 times. In order to improve the queries that have scanned, because they use an additional column I guess, I would like to change ...
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1answer
110 views

Clustered Index Help, where did i go wrong?

I was asked to review a very busy table and identify any areas of improvement. I have very limited power to change the table just the indexes. Table information 240 columns ~5 million rows Read ...
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1answer
60 views

Index usage and update statistics do not correspond?

In order to discover unused and wrong indexes in sql server I went through the following article: https://www.mssqltips.com/sqlservertutorial/256/discovering-unused-indexes/ It gives two queries ...
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Slow Tally Tables

I have a pain point with a relatively large application concerning 'tally tables', which are used for keeping track of the number of items against 'campaigns' (placed by a client), and 'publishers' / ...
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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 ...
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Should the index on an identity column be nonclustered?

For a table with identity column, should a clustered or non-clustered PK/unique index be created for the identity column? The reason is other indexes will be created for queries. A query which uses a ...
2
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1answer
62 views

Ways to Reduce Database Size and possibly improve performace. Untouched enviroment.

I am new to an environment. The Databases are virtually untouched by a seasoned DBA. I am looking for ways to reduce DB size and possibly improve performance. Unfortunately, I only have WEb edition ...
2
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1answer
59 views

How to optimize the sort in Postgres query

I've been trying to optimize the sort in the following query. I ran EXPLAIN ANALYZE and the majority of the time is during the sort when it arranges the output by distance. I've tried converting the ...
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143 views

Intentionally corrupting an index in PostgreSQL

I need to know if there is any method for intentionally corrupting an index in PostgreSQL. I have been searching for it for a long time but never seen anyone mentioning such an act.
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1answer
250 views

Row with latest timestamp

How to get the row with the latest value in a TIMESTAMPZ column? Is an index needed? Does an index change the strategy? Would behavior vary by database (I'm using Postgres 9.4)? My app records data ...
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Separate indices for the field I want to get the MAX() and the ones in the WHERE clause

My customer's database has a gigantic table (hundreds of millions of records) and a SELECT that, by cumulative use, is eating a huge chunk of processing time. Each exec takes almost a minute in ...
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1answer
58 views

Index based on another index [closed]

Assume a mysql table with columns A, B, C, ... . There are one composite index based on columns A+B+C. Combination of values A, B and C is unique, so this index forms the primary key. Now, a second ...
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1answer
188 views

Excessive CPU use in vendor SQL Server DB

Background: I've got a SQL Server 2012 DB provided by a vendor so modification of queries and tables is limited. We do own the DB though, so we can add and maintain indexes. Indexes haven't been ...
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1answer
32 views

Index design question

This query runs for 60 seconds: SELECT mychecklis0, .... FROM dbo.MyChecklistStatus mychecklis0_ WHERE mychecklis0_.AppFormSubSectionId=@P0 AND mychecklis0_.ProfileId=@P1 There is an index created ...
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How to do Statistics in Partial Indexes of PostgreSQL efficiently? [duplicate]

This answer motivated think again my following tables but I am still uncertain how to store variables/results from data analysis for quick selection in post-processing. If stored, I think it is well ...
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1answer
132 views

mysql query choosing an incorrect execution plan

I have a primary with an dependant subquery as a where condition that is choosing a wrong execution plan, and therefore is running for ever. Main query: SELECT rtr.id AS id156_, ...
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68 views

Reorganize Index Task [closed]

Can the Reorganize Index task (maintenance plan or SSIS package) be used to tune performance? Is this an adequate step of triage for degraded application/query performance?
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245 views

Dropping old and creating a new clustered index

I am wondering what is the best approach for dropping and creating a new clustered index on a table within SQL Server 2008. My primary concern is the length of time it will take to perform this ...
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204 views

Index optimization and cardinality

I'm by no means a DBA expert. Rather, a Magento developer having to troubleshoot some slow queries. I'll jump right in -- here's my attempt to EXPLAIN the troublesome query: EXPLAIN SELECT ...
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223 views

Is there some tricks to better index a URL column in postgres?

I'm working with a table that needs fast retrieve rows by its url column. But they all will be starting with http://www.: http://www.google.com http://www.amazon.com http://www.stackoverflow.com I ...
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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 ...