In the context of a database, optimisation refers to the process of the query optimiser selecting the best query plan to execute.

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Sorting of results is slow some times but fast at other times

I have a mysql query that is joining a few tables and then uses order by field for sorting. It sometimes runs quite fast at other times it is slow. While it was slow i profiled the query to find that ...
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19 views

How to store temp tables in memory during table “optimize”?

When optimizing tables, SHOW PROCESSLIST lists it as "copying to tmp table". I'm trying to ensure the copy takes place in memory to speed up the process. I've tried adjusting the tmp_table_size to ...
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65 views

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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17 views

How can I apply heuristics to optimise an expression tree?

I've converted the following SQL query: SELECT name FROM dog d, works_at w WHERE (d.owner_name = w.person_name) AND (w.kennal_name = "Breeders"); into the following expression tree: My main ...
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1answer
53 views

Clustered composite key high fragmentation and fill factor

I've recently made a table to hold the language preferences of my users as follow: CREATE TABLE [dbo].[systemUserLangPreference]( [systemUserID] [int] NOT NULL, [langID] [int] NOT NULL, ...
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38 views

What's the best way to translate a website [on hold]

I have a website in Django using MySQL, and I have more than 4.000 entries that I want to translate. What's the best way to do it? Create a new database for every language? Create other table for ...
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40 views

explain plan ,joins and optimization

I have to join 6 tables in sql query and each of these tables have 1 join to each of there master tables . Hence i have defined 5 subqueries within a sql query but i am seeing a lot of performance ...
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1answer
24 views

Optimize query with indexes

The following query is looking for all towns that are between 5 and 10 kilometers from a hard-coded latitude/logitude (=another town actually). I have 37010 towns. I'm using Symfony 2 which "creates" ...
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1answer
71 views

How can I speed up a Postgres query containing lots of Joins with an ILIKE condition

I have an odd problem which I really don't understand. Simply put I have a join containing 4 table joins, which I believe all have appropriate indexes, but which takes a ridiculous amount of time to ...
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21 views

Truncating Table Partitions Containing Data and Global Indexes

I have to truncate a partition (392,000 records) of a table with 20.000.000 records. At the moment, I'm making a truncate table and rebuilding indexes. But the table has 37 indexes and it takes 20 ...
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1answer
70 views

Inserting to table: Insert rows with Left Outer Join or Insert rows then Update?

I have a table of Orders and another table of Deliveries. The Orders table will contain a reference to the Deliveries table if there is a corresponding row. Not every row in Orders will have a row in ...
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1answer
58 views

How to index WHERE (start_date >= '2013-12-15')

I have a table named items, and inside the table there is a some_date column, with date as the datatype. I was wondering how can I index the some_date column with PostgreSQL SELECT "items".* FROM ...
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25 views

MySQL Query Cache - what type of queue is used?

I am wondering what type of queue is MySQL Query Cache using. When there is new query and cache is full which query is deleted? Oldest one? One with fewer number of hits? Or maybe there is some ...
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1answer
30 views

How to make make my query run fast?

How to make this query run faster? Table contains over 2 million rows of data and takes around 30 to 120 seconds to process the query. SELECT INET_NTOA(blocks.startIpNum), ...
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2answers
201 views

Optimized query to fetch a record from 10 million entries

A table has 2 fields | UniqueKey | TimeStamp | ------------------------- | xfsddddq | 1024125412 | | xfstttdx | 1024125413 |< | xfsdxxau | 1024125415 | Estimated, there are 10 million ...
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1answer
43 views

MYSQL Stock Database Optimization

I am downloading a bulk of stock data: Ticker symbol, company name, industry sector, Open, high, low, close I was wondering performance-wise if separating the ticker, company name, industry sector ...
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1answer
31 views

Design for hierarchical embedded database

The goal is to construct a hierarchical database of Objects having the following format: TypeA -> ObjectA [values, contains ObjectB*, ObjectC*, etc.] TypeB -> ObjectB [values, contains ...
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23 views

Optimizing PostgreSQL 9.0.2

For work we have a 8GB Linode, hosting both the Rails 3 App (Passenger, Apache) and Postgres. The app is a reading heavy app, about 75% reading, and 25% writing. (A conservative estimate would be ...
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49 views

Tagged questions

I have similar to StackExchange network that utilises tagged questions. In my web application Users also can find questions by tags. The query below returns a set of tagged questions: SELECT ...
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29 views

How can the performance of a query that has a condition on two fields of each row be improved?

I have an images table with approximately 5 million rows in it. For the purposes of this question lets say the table looks like this: CREATE TABLE `images` ( `id` int(11) NOT NULL AUTO_INCREMENT, ...
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26 views

MySQL: Large data slow reads

I have very large table with 17,044,833 Rows and 6.4 GB in size. I am running the simple query below and it takes like 5 seconds. Any ideas what optimizations can I do to improve the speed of this ...
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53 views

Opimizing Mysql

Below is a Snapshot of my Server info. And the results of mysqltuner.pl Some help with commands would be appreciated. I'm new to this and have gotten pretty far, but I'm having issue with Mysql ...
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22 views

Why is adding a FK constraint slow in MySQL?

I'm doing some experimentation in MySQL 5.1.53 and I've run across a case that I just don't understand. CREATE TABLE A ( `pk` INT(11) NOT NULL, `fk` INT(11) NOT NULL, PRIMARY KEY `pk_A` ...
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1answer
50 views

Will a specific denormalization increase performance in a specific scenario?

Suppose I have a table with fields | a | b | c | d | ... | z | which contains millions of records and which will serve millions of queries a day. And the field z holds the id of some parameter which ...
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1answer
62 views

Has postgresql a fast add column optimization?

When adding not-null columns with a default value - does Postgresql optimizes this operation? In case the table has n rows, a not-optimized alter-table-add-column would yield n writes of the default ...
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53 views

mysql optimize group by having count

I have 2 mysql table: table t1: CREATE TABLE IF NOT EXISTS `t1` ( `id` bigint(20) NOT NULL, `url` varchar(255) DEFAULT NULL, `title` varchar(255) DEFAULT NULL, `type` varchar(255) DEFAULT ...
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Indexes for SQL query with WHERE condition and GROUP BY

I am trying to determine which indexes to use for an SQL query with a WHERE condition and a GROUP BY which is currently running very slow. My query: SELECT group_id FROM counter WHERE ts between ...
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2answers
82 views

optimization of expensive subquery

The following query gets the last report (where latitude and longitude and secs are <> 0) associated with the specified units: SELECT reports.* FROM reports INNER JOIN ...
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2answers
53 views

index for OR operator with different columns

What would be best index for this kind of query: -- id is the PK create table test3(id number,name varchar2(30) not null,lastname varchar2(30) not null); select id from test3 where id=:1 and ...
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1answer
50 views

Can this where in subquery be optimized?

Currently the query takes ~ 0.2 seconds. Is this the best it gets? Because it feels rather slow for the amount of data I have in my database. I've tried creating an inner join out of it but I can't ...
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1answer
133 views

How can I speed up this query on table with 65 million records

select hash_id, hash_value, substring(T.cri, 1, 7), substring(T.cri, 9, D2.Pos-9), substring(T.cri, D2.Pos + 1, D3.Pos - D2.Pos - 1), ...
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1answer
191 views

Can I rely on this SQL shortcut to save a query?

Consider a table with a status field that holds one of two values: | status | set('active','default') | YES | | active | I need to know how many records are in the table, and additionally how ...
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18 views

Optimization for a dynamic M2M value field

I'm using a Configurable Product methodology in my system. Everything works great, but I have one thing I think that might strongly impact the performance in the future. This is a dynamic linking ...
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1answer
26 views

MySQL hangs in killed state

I have a strange situation where a mysql OPTIMIZE query will never end. After killinh it, it remains in the "killed" state. Scenario to reproduce: OS: CentOS 6.5 MySQL: 5.6 Engine: MyISAM (with at ...
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32 views

query comes in slow query when log_queries_not_using_indexes is enabled

This query comes in slow query log when log_queries_not_using_indexes is enabled. SELECT a.id, d.id AS city_id, d.city FROM booking a, sub_area_master b, area_master c, city_master d WHERE ...
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33 views

expdp taking so much time

I'm doing a full export using the expdp tool. I'm using 4 dump files and parallel parameter with 4 value. The export size calculus shows 30Gb but it takes almost 4 hours for 4 Gb. I'm pretty confused ...
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1answer
51 views

How can I optimize this query?

I'm trying to select the time field from five tables and return the oldest time. The userid field in every table is indexed. Here's the query: ( SELECT `time` FROM `eventlog` WHERE userid = ...
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1answer
56 views

Optimising an Update statemement with a very large Where clause

I have a table (TableOne) with a field called [ReviewNote], this table has more than 1.5 million record, I have to assign keywords to each record based on the content of the [ReviewNote], using ...
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30 views

Which of these two queries is better - can be optimized more?

With regards to the usage of the IF statement, which is better to use? Query #1: SELECT whatever FROM auctions AS a LEFT JOIN ............... WHERE ............... ORDER BY ...
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1answer
97 views

Specifying columns in LEFT JOIN through subquery beneficial performance wise?

I'm trying to understand how JOINS are handled, and was wondering about the following: Imagine a big query concerning a lot of tables, I'm really looking for small optimizations as it's a pretty ...
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46 views

How do I perform a batch update on the first n matching rows?

I need to perform a large number of updates at the same time. Each update needs to only affect up to a specific number of rows even though the WHERE clause might match to many more rows. So far, I'm ...
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1answer
44 views

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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1answer
83 views

INSERT take too much time

I have in my MySQL DB a few tables Most of the time, I'm only doing INSERT in my db. I have up to 4 connections to the DB, each one inserting into a different table. There cannot be two connections ...
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47 views

Alternatives for subquery

There are three tables: product_hits, products, and product_subcategory_map. I want to count the number of product_hits and for each product. There could be more than one subcategory in the ...
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1answer
147 views

InnoDB: very bad performance on INSERT/UPDATE

Lately I have really big problems with INSERTs and UPDATEs. On my website 80% of all queries are SELECTs but in query slow log there are only INSERTs and UPDATEs. My dedicated server has 32GB RAM, ...
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1answer
176 views

Improve Insert performance for 200 Million rows

How can the following insert statement be improved - which varies from 20mins on certain days to 70-140mins on most other days. SELECT DISTINCT od.SourceID, od.OrderID, od.OrderLineNo, ...
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47 views

Optimize query to minimize tmp copying time

I have this mega query : SELECT s.eleve_id, crs.id_cours as 'cours_id', mc.code as cours_code, s.employe_id, s.id_seance, '0' as theorique, s.statut, s.type_vehicule_id, s.type_conduite_id, ...
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Is this a normal query time for a left outer join type?

I have Employee Table - 80K records about 100 fields I have an app table - 8K records and 30 fields Then a subset of employee table also stored as table that has our divisions subset - call this ...
2
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1answer
80 views

Optimize table and query, aggregate by date or date-hour

I have a table storing sensor data (100M rows currently) from stations from different sites. In my case, sites may have many stations. Create table statement is as follows: CREATE TABLE sensor_data ( ...
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209 views

Optimize a MySQL Database using MySQL Workbench

I actually have a few issues. First, I found this information about optimizing: MySQL OPTIMIZE all tables? The problem is, I don't seem to have a mysqlcheck program anywhere. I'm using MySQL ...