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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Sql server table insert performance optimization

Setting In a datawarehouse, I am joining a fact table to 20 dimensions. The fact table has 32 million rows and 30 columns. This is a temporary staging table so I don't have to deal with other users ...
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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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Mysql Memory table getting many locks

On my site I log every pageview (date, ip, referrer, page, etc) in a simple mysql table. This table has the following activity: 1 SELECT per minute 1 DELETE per minute no UPDATE queries Lots of ...
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How to optimize very slow SELECT with LEFT JOINs over big tables

I was googling, self-educating & looking for solution for hours but with no luck. I found a few similar questions here but not this case. My tables: persons (~10M rows) attributes (location, ...
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Slow index scans in large table

Using PostgreSQL 9.2, I have troubles with slow queries on a relatively large table (200+ million rows). I'm not trying anything crazy, just adding historic values. Below is the query and the query ...
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Why does SQL Server run a subquery for each row of the table it's qualifying?

This query runs in ~21 seconds (execution plan): select a.month , count(*) from SubqueryTest a where a.year = (select max(b.year) from SubqueryTest b) group by a.month When the subquery ...
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if database is not shrinked does it affect backup size?

Ok my question is simple. Lets say that when i click database and hover over shrink it says it can be reduced 1 GB space. Now when i do a backup of this database, does this space also getting added ...
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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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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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Why is the CTE much worse than inline subqueries

Im trying to better understand how the query planner work in postgresql. I have this query: select id from users where id <> 2 and gender = (select gender from users where id = 2) ...
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MySQL queries are 10 to 100 times slower after OS reboot

I have a MySQL server running on Ubuntu. If I restart the MySQL, everything is fine. If I however restart the OS, my queries take anywhere from 10 times to 100 times as long. The only "solution" to ...
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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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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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130 views

How to get the information of the optimizer of PostgreSQL?

I am curious about the information like total optimization time the time spent on each stage of optimization the number of alternative plans and the cost of each alternative plan.
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119 views

can sql generate a good plan for this procedure?

I have read that procs that do not always do the same thing per se, will not always have a good plan generated. That is (correct me if I'm wrong), if I have a proc that if the day is even it reads ...
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576 views

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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Optimizing queries against a set of tables that contain partitioned data

I have a third party program that creates and populates a series of tables to hold some historical data: data_33 -- contains data for 12/01/11 - 12/05/11 data_34 -- contains data for 12/05/11 - ...
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535 views

Optimizing queries on a range of timestamps (one column)

I am using Postgres 9.3 through Heroku. I have a table, "traffic", with 1M+ records that has many inserts and updates every day. I need to perform SUM operations across this table over different time ...
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JOIN on 3 tables being slow

everyone. Can't figure out what indices are missing or how to rephrase my query. I created about a milllion of test entries in each table to see performance. Query takes about 1.5 seconds which is ...
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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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Website is too slow when number of records increases?

I have developed a web application called Referral Program, It it developed by using PHP, MySQL. Users can joining the website and when they introduce new members, he/she gets a commission. The system ...
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A lot of ad-hoc queries impact on server

We have a third party application which generates a lot of ad-hoc statements (our server has 16GB of memory and there are 140000 ad-hoc queries present in the cache).I've enabled 'Optimize for Ad-hoc ...
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537 views

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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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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807 views

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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Understanding optimisation of complex SELECT queries

I have a people table with basic contact info in. I have a bunch of criteria that can select Id values (fields called pid) from the people table. I want records that match ((criterion 1 or criterion ...
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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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Help optimizing MySQL slow query

i'm running a wordpress which needs some mysql optimization, i have a slow query and i would like to get rid of "Using temporary; Using filesort" query: EXPLAIN SELECT SQL_CALC_FOUND_ROWS wp_posts.* ...
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How to determine cost/benefit of adding an index?

According to Craig Ringer: While it's usually a good idea to create an index on (or including) your referencing-side foreign key columns, it isn't required. Each index you add slows DML operations ...
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Logical optimization of joins and selections

I am studying query optimization. I have read that it might be preferred to apply relational selections before a logical join operation. Is there a scenario where joining first and then applying ...
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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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299 views

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 ...
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MySQL: A better way to write this query?

We are using the following query in our system: SELECT f.type AS type, COUNT(i.id) AS submissions, SUM((CASE (e.oiPost + e.oiPhone + e.oiEmail) WHEN 0 THEN 0 WHEN ...
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How to use the METHOD_OPT parameter in DBMS_STATS.gather_table_stats

Hi there I was just wondering what would be the difference between these 2 METHOD_OPT parameter settings: FOR COLUMNS SIZE 5 some_column and FOR COLUMNS some_column SIZE 5 both will create a ...
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SQL query filled Temdb complete Harddisk [closed]

I have a query which was earlier fine but now it is running me out of hard disk space with message that tempdb is full. My Harddisk has 90 gb of space as soon as i run query temdb runs out of space in ...
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Improving select query

I was at an interview for a new job today and got asked a question regarding a SELECT query: SELECT lastname FROM users WHERE name='John'; This SELECT query is to run over a million rows. I was ...
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SQL server tools to identify query optimisations and missing indexes [closed]

I have a broad question regarding SQL Server that was given to me on a quiz and I am not sure what the answer is as I do not have access to SQL Server at home. My question is how can I utilise SQL ...
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Optimizing a Postgres query with a large IN

This query gets a list of posts created by people you follow. You can follow an unlimited number of people, but most people follow < 1000 others. With this style of query, the obvious optimization ...
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SQL Server Baseline and Performance Optimization

I've been struggling a little bit around Performance Troubleshooting including baseline and troubleshooting of SQL Performance. Could anyone help with this or point me to where I can possibly get a ...
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How does TOPN influence a query with group by?

I have a query that looks like the following: Select t1.field1, t2.field2, sum(t1.field3) From t1 inner join t2 on t1.id = t2.id Group by t1.field1, t2.field2 It's simplified, normally there are a ...
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Does combining columns into 1 column helps to optimize a large table?

I have user, items and user_items tables, and as usual user has many items. Tables contains: User: ~50K Items: ~3.5M UserItems: ~5M I am using MySQL and most of my queries are selecting items of a ...
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Optimizing a query which runs through all hours in a day

I need help optimizing a query. I'm using PostgreSQL 9.3.4 currently but can upgrade to 9.4 if needed. I have a table with 60+ millions of records which looks like this: ...
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What are the options of reducing tempdb latency?

Took the job of monitoring and tununing a SQL Servers 2012 Enterprise Ed. SP1 (64 bit) on Windows Server 2008 R2 Standard Ed. All of them are running inside virtual machines. One SQL Server per a ...
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Maximum possible memory usage: 16.2G (874% of installed RAM)

Why the MySQL is saying that can use about 16GB of RAM even if my server has only about 2GB? # ./mysqltuner.pl >> MySQLTuner 1.2.0 - Major Hayden <major@mhtx.net> >> Bug ...
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Searching for pairs of date/time values in a single row

I have a legacy IBM DB2 database table that contains lots of records of phone calls. It has columns for ID, customer number, employee who took the call, etc. The date/time for each call is kept in a ...
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Mysql Index for concat select

For Below Query SELECT MAX(CONCAT(date, ' ', last_entry)) AS LAST_LOG FROM entry_log WHERE TRIM(LEADING 0 FROM card_no)='2948' I've index on date card_no date,last_entry ...