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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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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1answer
268 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 ...
4
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1answer
230 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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1answer
205 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 ...
2
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1answer
316 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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335 views

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

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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0answers
89 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 ...
0
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1answer
452 views

Why query optimizer doesn't use negative filter index

I have a table that has following structure, as you can see, there are one clustered index and two non-clustered indexes, one non-clustered index is IX_ParentId_Include, and another one is ...
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2answers
54 views

Should I include as much information as possbile to help the optimiser?

Reading the article "Dynamic Search Conditions in T‑SQL" I saw the following statement in the "Using sp_executesql" section. Double Feature You may wonder why there are two conditions on the ...
0
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2answers
93 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" ...
2
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1answer
247 views

Most efficent DELETE Method

I must choose between three possible DELETE methods in SQL Server. The table: RawData stays at around 500GB. Here is the table: CREATE TABLE dbo.rawData ( rowId INT IDENTITY PRIMARY KEY, ...
4
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1answer
136 views

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 ...
1
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1answer
2k 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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6k 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 ...
0
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1answer
470 views

sql-server optimize query with lots of null checks

I have a query such as: select something from somewhere join stuff on condition join more_stuff on condition where somewhere.sometime is null and somewhere.someone is null and stuff.whatever is null ...
2
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2answers
679 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 ...
0
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1answer
115 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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0answers
197 views

How can I get rid of the “No Join Predicate” warning

I have this fairly straight-forward snippet of a query: DECLARE @ClientGUID numeric(16) = 9000011916900200; SELECT ch.GUID, c.LastName, c.FirstName, mrn.ClientIDCode AS MRN FROM Client c INNER ...
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1answer
90 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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468 views

How to make make my query run fast? [closed]

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
2k 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
687 views

When tables are locked does MySQL queue queries?

I have a small production website, but it's live 24/7. When running the Optimize, Analyze or Repair commands, MySQL locks the table it is working on. QUESTIONS How would this effect users trying ...
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1answer
227 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 ...
0
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1answer
69 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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70 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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51 views

Set default fields

Is there a way to inform the database that some fields are default (have always the same value) so that I don't need include them in all my queries? Suppose: Select ... where f1=a, f2=b, f3=c, f4=d ...
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107 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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308 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
91 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 ...
3
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1answer
728 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 ...
2
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1answer
891 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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3answers
2k views

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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114 views

MySQL query with order by decreased performance

Here is my schema: CREATE TABLE `UserMst` ( `UserID` mediumint(8) unsigned NOT NULL AUTO_INCREMENT, `EMailID` varchar(50) DEFAULT NULL, `UserName` varchar(20) DEFAULT NULL, `FullName` ...
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361 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
142 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 ...
0
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1answer
76 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 ...
0
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2answers
1k 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), ...
0
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1answer
66 views

SQL query optmization [closed]

This is one thing I have been trying to read from few days. I am not getting any satisfactory explanation anywhere. Tried surfing some blogs and videos in youtube. Appreciate if anyone one can throw ...
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1answer
211 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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47 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 ...
2
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1answer
2k 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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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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1answer
62 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 = ...
0
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1answer
116 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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0answers
32 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 ...
2
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1answer
826 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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324 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 ...
5
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1answer
55 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
1k 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 ...
2
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1answer
497 views

Is there any way to save the execution plan in a file in PostgreSQL?

By saving a plan in a file, I don't mean to view it, but force the optimizer to use the saved plan to execute some query. For example, if the optimizer chooses to do a hash join for a two-table ...