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: Optimize query with a range and distinct count

I have a query on a large table with millions of rows that looks like this: SELECT COUNT( DISTINCT clicks.tx_id ) AS unique_clicks_count , clicks.offer_id FROM clicks WHERE ...
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11k views

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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101 views

Simulate more RAM with SQL Server

Background: I'm in the process of optimizing a Data Warehouse style query with big dimension tables. The optimizer does not like to pick the typical star schema join plan at the moment. When I force ...
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54 views

If a database is in memory does it still need indexing?

INFO I'm following lessons on databases. We're learning about indices now. Question If big parts of a table are in the memory, would using a index still have benefits? My side I would assume ...
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37 views

optimize my query mysql

I have the following query: SELECT DISTINCT d.movieName, d.castName, d.movieImdbId, f.year, f.posterLink FROM director_movie as d LEFT JOIN film_info as f ON d.movieImdbId = f.ImdbId WHERE d.castName ...
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371 views

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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71 views

How to use max function in such condition?

My query is select * from guestuser union select * from olduser ORDER BY userid DESC LIMIT 1; Is that correct query to find last userid from different table have different userid? can i change ...
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56 views

Slow MySQL Query when Ordering

This query takes around 2 seconds when the order by is included, without the order it takes less than a tenth of a second. The field that is doing the sorting, qc_products.addedDate, is an index and ...
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135 views

SQL execution 2 seconds with LIMIT parameter, without only 0.2s why?

This is my query and I need to return only 12 rows, but it takes 2 seconds with parameter LIMIT 12 while it takes only <0.2 to process all ~600 results (without LIMIT 12 or with LIMIT 1200 for ...
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62 views

Table design for optimum performance

For example let's say I have to create a table called Employee with columns EmployeeID, Name, DOB, Address, DepartmentID[FK]. So I create the table as follows with a primary key and a nonclustered ...
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170 views

Simple query is slow on 4M-rows table

I have in production a MySQL table pageviews with 4M rows that records page views of users on posts. I need to know which posts a specific user have read, but this request takes up to 15 seconds to ...
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75 views

PLSQL using cursors or functions to query repeated data

Is it better to declare a commonly used lookup query as a package function or as a function (either returning rows or values or returning a sysref cursor)? Whats the difference? What are the best ...
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265 views

MySQL - OPTIMIZE TABLE for partitions

I would like to perform OPTIMIZE TABLE opearation , this table is a partitioned table. Which method can be better in this scenario: OPTIMIZE TABLE tblname; or ALTER TABLE tblname ...
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300 views

How to manipulate join order of PostgreSQL optimizer?

I am working on table join order optimization. While query processing, I want to get table join order generated by optimizer, and update it by using my own algorithm in PostgreSQL? How can I update ...
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4answers
180 views

DB performance vs replication

I am working on a db optimization (planing for future project growth) and need some help. Currently, every table is using uniqueidentifier as PK (clustered index) and we have high index fragmentation ...
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1answer
74 views

optimizing query for slow queries

I have this query in my slowqueries table which essentially is taking about 5-8 seconds to complete the query time: SELECT s0_.id AS id0, s0_.updated AS updated1, s0_.created AS created2, ...
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218 views

Performance tuning self-joining MySQL query

I asked a question recently on the correct way to update a table using multiple joins to itself in order to generate the desired values. Updating MySQL innodb table based on multiple joins After ...
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59 views

MySQL optimize range duplicate query

I need to eliminate duplicates from a time sheet. I found this solution and have adapted it for my own needs: DROP TABLE IF EXISTS `activity`; CREATE TABLE IF NOT EXISTS `activity` ( `id` int(11) ...
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220 views

Configuration help my.cnf Mysql

Is the following my.cnf file OK for a dedicated server with 56GB of RAM (on ubuntu server and 8 processors)? I'm running just one website on the server and there is a high demand on my cpu from ...
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121 views

How to optimize update using join in postgresql

I'm using PostgreSQL 9.3.5 on a CentOS system. I have a very large table (twenty million rows, 50+ column) that aggregates data from a few hundred systems. Several times a day each of the systems ...
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118 views

Optimizing SELECT queries

I'm not very experienced with database query optimization. I've been reading through similar questions here and Postgres tuning articles online, but unfortunately I haven't had any luck. Here's what I ...
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1answer
183 views

Is there a way to force one optimization level in SQL Server?

Based on Paul White's blog, there are three optimization phases in SQL Server, search 0(Transaction Processing), search 1(quick plan) and search 2(full optimization). Each phase has entry and ...
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2k views

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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239 views

When is mariadb creating tmp tables?

I have found, that copying to tmp table is taking most of the time of a slow query, that I wanted to optimize. I watched the output of 'profiling' in a terminal. This happens on a pics table with 6000 ...
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815 views

Slow postgresql query with pagination and filtering

For the DB in question, I have followed the advice of Pagination Done the PostgreSQL Way That is, results are being paginated on a composite index with a definite sort order. Now, my problem is ...
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62 views

Oracle estimate cardinality on partitioned table

How does Oracle estimate cardinality on a partitioned table if the query gets the list of partitions from a subquery or a join? For example, if I have a query like this select * from ...
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37 views

Join Operation using index defined?

I need to optimize some queries with several joins. I plan to create some indexes for these queries. I am currently using MariaDB with TokuDB storage engine. Should I expect the indexes for the join ...
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How to Search a Database of Package Deals for Specific Items with the Fewest Unwanted Extra Items

Short Description I have a database of special offers that bundle several items together. I want to be able to search for a list of specific items and get a combination of bundles that includes all ...
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62 views

Help with optimising a sql query on two partitioned tables

I have a SQL query that I am running on two very large tables in SQL Server 2012 Enterprise The two tables are ACKs and Logs. Both are partitioned on their time by day column with the appropriate ...
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102 views

How to setup large database access/cache on LAMP environment? [closed]

My application is getting very slow I guess because of the ever growing database (30+ tables some with 50,000+ rows). Using CodeIgniter's model tier to call MySQL database, I optimized queries & ...
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270 views

Optimisation and Performance Mysql , Zend Framework 2 and Doctrine 2?

i'm facing some problem with performance in an application using zend framework2 and doctrine 2. i would like to optimis it but i don't know from where to start , i read some many questions/ answers ...
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162 views

What is the best storing device for DB transaction log?

I'm using MySQL with InnoDB storing engine. Transactional log is placed to dedicated HDD. Still as it is HDD atopsar shows big load (>50%) to this HDD because of big amount of small IOs (about 50 ...
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206 views

Speed Up Index Creation in MySQL

In MySQL 5.5, I have a table which is recreated on a daily basis and for which the process of adding an index is taking about 50 minutes which I'm hoping to reduce. At the time when the index is ...
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169 views

Reading a SQL Server Execution plan

I am very new to any type of tuning but have been learning more.. One of my specific databases one of the problems identified with slow queries are a number of Implicit conversions. It is my ...
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215 views

Appropriate use of mysql Optimize Table

I want to come up with some best practice for maintaining our mysql database. versions 5.5/6 and using InnoDB. i came across this artice - ...
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96 views

Is it normal that I have to FLUSH QUERY CACHE once every 6 hours to maintain fast queries?

I am running MySQL 5.5.37. I have a cronjob set to run every 6 hours to flush the query cache. I realized that if I don't do that, then the cache becomes fragmented and average query response time ...
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124 views

How to add an “INCLUDE” part in an Index Created as a part of CONSTRAINT

I am going through the execution plan of a tsql query. There is a key LookUp (Clustered) in the plan. To avoid this Key LookUp, I tried to Include a column (Status_Ind) to The Index (The Index ...
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2answers
736 views

MySQL InnoDB log files on different location

I am using MySQL version: 5.5.38 There are following parameters that can control InnoDB log files: innodb_log_files_in_group - amount of log files in the group, by default 2. Will create 2 files ...
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724 views

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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685 views

Index optimization for table that is truncated every day

I have a bunch of tables in SQL Server 2012. These tables are fed by other tables. Every day there are routines that truncate (fully delete) them and run queries whose result are inserted into them. ...
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94 views

Explain plan shows a table not in the query

In trying to optimize a 2 minute query against an SAP R3 Oracle database, I examined the Explain Plan in Toad and found that most of the query's time is spent on a table that isn't even in the query. ...
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831 views

MongoDB performance problem

I have a MongoDB for storing result like this {_id, type, imei, lat, lng, spd, dir, time} {_id, type, imei, lac, cid, time} If type is f first one is used and if it is l second one is used. Here ...
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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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43 views

Should I drop this column or is there a query that can achieve a results table without duplicate columns?

I use a column named active in several of my database tables to adjust whether a particular entry/row/user/etc should be included in future query result tables instead of deleting the information. ...
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63 views

Optimised way to search over 2 milllion poi data in mysql

We have over 2 million poi data in our mysql db. At any time we need to find what is the nearest point based on the following formula found at this link http://sqlfiddle.com/#!2/abba1/4 select *, ( ...
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78 views

Optimal way of loading, registering, indexing and querying a huge XMLDB

I've got 35 million highly structured XML documents, with a total size of 500 GB. An XSD is available for this data, and the end goal is to transform the data into an RDB. All fields can be considered ...
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2answers
1k views

How to break table into two without losing performance?

According to http://stackoverflow.com/a/174047/14731, splitting away infrequently-needed columns frees up the cache allowing faster retrieval of the commonly-used columns. I've got a table whose ...
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2k views

Multi-Column Full Text Search Going Very Slow

I have a full text index on a table articles for the columns content, title and keywords When doing the search on each of the columns, like so select count(1) from articles where ...
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349 views

Best way to store few rows of data every minute without creating 1440 columns a day?

I will be calling a server that returns some JSON data every minute. The values are along the lines of Value, Currency, DateTime, and maybe 1 or 2 more values. What is the best way to keep save these ...
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280 views

optimize the query with big and low cardinality

I have big enough dataset and few joins to get them all with help next query: SELECT DISTINCT c.c_id FROM c_active z1 INNER JOIN cs c ON (z1.cv_id=c.cv_id) INNER JOIN indi i ON (c.m_id=i.m_id) INNER ...