In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

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MySQL Query Optimization : Indexing and Pagination

I'm adding pagination to my 'latest news' php script and running in to an issue. SELECT sid, title, time, bodytext, author, url FROM news WHERE approved=1 ORDER BY time desc LIMIT $start, $limit I ...
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optimizing a compare query

Suppose I have two tables, A and B, and I know that size(A) = size(B). I want to confirm that the data in both tables is the same in three given columns, suppose they are X, Y, and Z (there are no ...
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Bulk Data Loading and Transaction Log

im currently working on a project which bulk import data from flat files(csv) about 18 differents files each linking to a specific table through some store procedure. I followed the steps as advised ...
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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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Is it possible to decouple row size estimation from maximum column width?

In other words, is it possible to declare a column VARCHAR(n) and have the estimated size be something other than n/2? An example use-case might be storing URLs - you expect most to be relative and ...
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Slow Queries Not Logging

I am attempting to enable slow query logging on our server in order to identify any queries that could use optimization. Sounds simple enough, however my file is not being written to. I get no errors ...
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Speed up INSERTs

I need to have a way to insert to a table, fast, synchronous, with minimal duration. What I've tried ("blind") is : Have no index on the table whatsoever Switch to simple logging (from full logging) ...
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REBUILD - Clustered Index, TABLE, or both?

I'm having trouble finding a definitive resource on this anywhere, so hopefully a guru can give me an answer here. I have a very large table that we had to add a column to. The clustered index is ...
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Database Indexing - Maintenance Jobs

I have created a script that runs every night to rebuild & re-organize indexes based on the fragmentation, Indexes with Fragmentation > 30% are rebuilt, Indexes with Fragmentation 10% - 30% are ...
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New query slower even if it has less logical reads than the old one

I have a query in a stored procedure that must list all dates in a range and JOIN on it date from a table, if it exists for that day. The procedure was created before I was employed as the DBA, so I ...
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Schema for analytics table in Postgres

We use Postgres for analytics (star schema). Every few seconds we get reports on ~500 metrics types. The simplest schema would be: timestamp metric_type value 78930890 FOO ...
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my.cnf values not applying - Optimizing MySQL in CentOS LAMP

I have checked for other occurences of my.cnf and I have found only one occurrence of /etc/my.cnf. Then, I went ahead to fix in my values, e.g. query_cache_size etc. After saving and literally ...
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Walking a BTREE index as far as possible in MySQL

Suppose one has a column of words on which one builds a BTREE index: CREATE TABLE myTable ( words VARCHAR(25), INDEX USING BTREE (words) ); LOAD DATA LOCAL INFILE '/usr/share/dict/words' INTO ...
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How to use merge hints to isolate complex queries in SQL Server

I can understand that if I join individual queries that are "individually fast" the combination may become slow because the default execution plan may be non-optimal. However when I know the number ...
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Determining which isolation level is appropriate

This is a homework question. For the following transactions state the isolation level that will maximize throughput without lowering the integrity of the database. Explain the answer. ...
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Query performance while using sqlcmd [duplicate]

Possible Duplicate: Running queries with SQLCMD vs. Running queries with SSMS I have a number of scripts that query the data from different tables and consequently update them. I have ...
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Where to look for a bottleneck after elimitating CPU, memory, and disk

I have a database job that runs each night to create a warehouse table. Using my new database server and SAN I have gotten the process down from 4 1/2 hours to 35 minutes. I have optimized it to run ...
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Is there a way to hint to query optimizer to MySQL which constraints should be done first?

This is my current query: SELECT BusinessID as ID, 111151.29341326*SQRT(pow(-6.186751-X(LatLong),2)+pow(106.772835-Y(LatLong),2)*0.98838574205337) AS Distance from ( SELECT * FROM ...
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How can I speed up “show columns” on MySQL?

My application depends on running "show columns" for certain tables. It takes about 60ms to run, whereas all our other queries take under a ms. Querying information_schema directly is even slower. ...
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SQL Server Optimization/Configuration for Inflexible Application

I'm responsible for overseeing an application which uses SQL Server as its backend storage solution. Unfortunately, the application has no concept of how a RDBMS should be utilized and seems to use it ...
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Optimizing my update sequence

Whenever a user updates his profile, we conduct a set of queries like so: DELETE FROM `user_likes` WHERE `ID` = $id INSERT INTO `user_likes` VALUES (DEFAULT, $id, $interest_id, $interest_name) Is ...
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Do cross-joins get optimised by the client library?

Note This is deliberately database agnostic, I'm interested in how different implementations, er, differ. I came across Joins are for lazy people on SO, and it's made me question an assumption I'd ...
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Does the order of fields in SELECT query matter when using composite indexing?

I understand that the order of columns in the index itself matters immensely; however, what about the order of columns in the subsequent SELECT queries that make use of that index? For example, if I ...
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“Copying to tmp table” extremely slow

This is my example of query: SELECT nickname, CASE class_id WHEN 1 THEN 'Druid' WHEN 2 THEN 'Necromancer' WHEN 3 THEN 'Mage' WHEN 4 THEN 'Priest' WHEN 5 THEN ...
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I've got 16GB of ram, how should I configure MySQL Server?

I've got a dedicated production server with multiple cpus and 16GB of ram. I would like to know how can I configure it better to take advantage of the server resources for better performance because ...
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Postgres: count(*) vs count(id)

I saw in the documentation the difference between count(*) and count(pk). I had been using count(pk) (where pk is a SERIAL PRIMARY KEY) not knowing about the existence of count(*). My question is ...
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250 billion rows - computing interconnectedness on a really huge scale

I have a table of approximately 700k rows, each identified by a unique itemnumber. Each row/item can be associated with any of the other rows/items in the table by calculating a single numerical ...
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How does the T-SQL optimizer handle “and false”

In SQL SERVER 2008 I'm thinking about a query such as: SELECT ... FROM ... WHERE ... AND @a=1 UNION SELECT ... FROM ... WHERE ... AND @a=2 Given that @a is clearly the same value, and therefore ...
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Huge database logging of event type rows and ways to optimize it

We have a database that stores events. Events are generated at a 1000 per sec rate. We need to keep these events accessible for some years. Usual use of these events is selecting some of them from the ...
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How to Correctly Estimate the Average Number of I/O Operations my RAID 10 disk can offer?

The average Input/Output Operations per Second a disk can sustain is a very important factor in the tuning of MySQL / InnoDB databases, as it drives the speed with which Dirty InnoDB Buffer Pool pages ...
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Fastest validation query in PostgreSQL

What is the fastest query in PostgreSQL, which I can use as a validationQuery binding a JNDI resource? I though that SELECT 1 is the simplest, but in this document it is said that in PostgreSQL we ...
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How to create multiple entries on index based on the fields of one row?

I never found a good way to index multiple fields of one row as entries of an index or simulate this feature on MySQL. The problem arises when you have fields working as tags or similar concept. Ex.: ...
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Can I optimize for the zIIP processor?

Is it possible to change SQL in a z/OS mainframe COBOL application so that it becomes eligible to be directed to the IBM System z Integrated Information Processor (zIIP)?
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Speeding SQL queries for a large(?) WordPress database?

I am using a WordPress plugin called feedwordpress in order to run a planet like website (it takes content from other websites, with their permission) on WordPress (See it here). The plugin is great ...
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Fetch first 9 records and make one more record which will be as “Others” in MySQL

I am fetching records from one table with count of one field with other field as name. I want only 10 records. out of which 9 records give me field and its count. but i want to show 10 record as ...
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ORDER BY optimization for a large table

I am currently aggregating posts from different social networks. Currently I have 50-100 million posts from Facebook, Twitter, Youtube, Instagram , Pinterest. Consider a table posts posts { id ...
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Simple MySQL query randomly takes forever

I'm having an issue on my server with a simple PHP send emails script that runs every minute via a cronjob. The script contains a MySQL query that runs very fast most of the time, but randomly will ...
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Optimal hash technique to index large text

Erwin Brandstetter thankfully saved me from myself when I tried to create unique indexes on textual columns with large lengths. The upper limit for the insertion rate is tens of billions of rows per ...
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sql indexing and performance

I am using mysql5.1, i have table which has about 15 lakh (1.5 million) records.This table has records for different entities i.e child records for all master entities. There are 8 columns in this ...
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Optimize MySQL Query using LEFT JOIN

I have a query with execution plan as below and is taking more than 20 seconds to execute how can i optimize it EXPLAIN SELECT c.coupon_id as c_id, `c` . *, `st`.`name` AS `store` FROM `coupon` AS ...
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Indexing strategy when using the between operator SQL Server 2008

I have a large table ~25 million rows with the structure CREATE TABLE [dbo].[rx]( [pat_id] [int] NOT NULL, [fill_Date] [date] NOT NULL, [script_End_Date] AS ...
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How much does table size affect performance?

Lets say I have a MyISAM table (amongst other tables) with 2938347 rows. This table is merely being used for logging and doesn't get emptied very often. By not regularly archiving or deleting these ...
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MongoDB optimization on high data

I have a mongoDB collection with 42M registers with 1M new registers every day. We found a low performance on mongoDB querying. showing in mongostat the fields: qr|qw ar|aw with values of 300-500. ...
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Measuring the relative performance of queries given the assertion that “cost” isn't reliable

The cost field is a comparative cost that is used internally to determine the best cost for particular plans. The costs of different statements are not really directly comparable. Source Does ...
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SQL Server Wildcardless LIKE Optimization

In a web application using SQL Server 2008 R2 as the backend, I have several fields, that if present, add WHERE clauses to the query. If I was to have all queries generated as like clauses, such as: ...
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Multi-row insert vs multiple single row inserts

In my app I do multi-row inserts when I can just because it reduces the number of round trips between the db and the app. However, I was curious, is there any other advantages? For example, if ...
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MySQL performance problem using indexed datetime column

I tried to solve the following problem for about one hour now and still didn't get any further with it. Okay, I have a table (MyISAM): ...
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View with fallback (performance/optimization question)

I have a table with tariffs for stuff; the tariffs table is not important in this scenario, the "tariff values" are. In this Demonstration SQL Fiddle the tariff_plan is the FK to the tariffplans table ...
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How to get the information of the optimizer of sql server?

The info like total optimization time, the time spent on each stage of optimization, the number of alternative plans and the cost of each alternative plan. Is there any way to get these info using sql ...
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Optimizing MySQL -

I've been researching how to optimize MySQL a bit, but I still have a few questions. MySQL Primer Results http://pastie.org/private/lzjukl8wacxfjbjhge6vw Based on this, the first problem seems to be ...