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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Is there a good reason to store big text data outside database?

I was analyzing my MySQL database performance and found that tables containing text fields are just huge, larger than 1Gb. This data is only used when loading single record (like article or blog ...
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3answers
132 views

Optimize extremely slow SQL query [closed]

SELECT j.job_id,j.last_updated,j.job_title,j.status, (SELECT COUNT(*) FROM candidates WHERE job_id=j.job_id) resumes_count, (SELECT COUNT(*) FROM candidates c WHERE job_id=j.job_id AND c.ref_type=1) ...
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2answers
1k views

How can I truly DELETE data from a SQL Server table - still shows up in notepad in backup file?

SQL Server DELETE only marks as DELETED though leaves as data in the data pages. Data pages are 1024 KB in size and this problem can be eliminated by adding a FILLFACTOR that ensures only 1 record ...
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2answers
345 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
255 views

PostgreSQL FTS and Trigram-similarity Query Optimization

I have recently started working on PostgreSQL and I have around 12M rows to handle in which I want to apply Full Text Search. I don't have any prior experience in handling such databases. I have tried ...
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2answers
79 views

Filesort while using primary key for orderby

I have been breaking my head for the past two days now for this. CREATE TABLE `clients` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `guarantor_name` varchar(50) NOT NULL, ...
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2answers
799 views

How can I better optimize my tables and a LEFT JOIN query to find items that don't yet exist in the right table?

I have two tables that represent a list of urls and their related word indexes. Here are the table definitions for reference. desc urllist; ...
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2answers
675 views

Use timestamp(or datetime) as part of primary key (or part of clustered index)

I use following query frequently: SELECT * FROM table WHERE Timestamp > [SomeTime] AND Timestamp < [SomeOtherTime] and publish = 1 and type = 2 order by Timestamp I would like to optimize ...
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1answer
498 views

Why do aggregate functions alter the way my rows are fetched?

Running this query SELECT s0.id, s0.symbol, YEARWEEK(p0.datetime) AS label, p0.id AS point_id, p0.datetime, KG_FIRST(p0.open, p0.datetime) AS open, MAX(p0.high) AS high, ...
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1answer
48 views

Optimization for 100 GB Real-time info table

I have a table of device information feed which is filled by data from remote device units. There will be like 1000 units each sending an update per minute which will be stored as a row in that ...
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2answers
64 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
44 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
200 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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1answer
377 views

Optimize MySQL Self JOIN Query

I have a query which is running in 15+ seconds SELECT t1.`ST_StockCode`, t2.`SM_StockCode`, t2.`ST_ItemSize` FROM `stocks` AS t1, `stocks` AS t2 WHERE ...
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1answer
489 views

How to measure a perfomance of SQL Server database? [closed]

I have the task to improve the performance of a SQL Server 2012 database (one of 4 in an instance) by 60% confirmed by corresponding statistics. So, I need to measure "performance" of the RDBMS ...
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2answers
256 views

How to index for a query with independent range conditions?

What is the best way to index a table that I query using independent range conditions? E.g. WHERE X < ? and Y > ?
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1answer
190 views

How to profile a particularly slow or inefficient query

I'm currently writing queries for my database but this is the first time I've dealt with large data sets of any sort, and I'm now finding that I need to improve the performance of my queries. ...
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3answers
622 views

Is it worth to separate columns into multiple tables for one-to-one relational table

I need to make a decision for database structure on whether to separate one-to-one relational columns into multiple tables and link with one relationship id or just add all columns into one table. ...
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1answer
606 views

Large INSERTs performance optimization

I have 15 Amazon AWS EC2 t1.micro instances which simultaneously populate Amazon RDS MySQL d2.m2.xlarge database with data using large INSERTs (40000 rows in query). The queries are send ...
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1answer
43 views

Misunderstanding statement in MySQL documentation

I can't understand this statement in Optimizing Data Size: Declare columns with identical information in different tables with identical data types, to speed up joins based on the corresponding ...
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1answer
490 views

Optimizing ORDER BY for simple MySQL query

I'm trying to optimize this really simple query, and it gives me grief for a day now :( Seems pretty straightforward, I need to select with a JOIN from 2 tables, and get top X results sorted in a ...
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1answer
240 views

Database schema design help needed

I am developing a PHP application expecting millions of records both parent and children. My goal is to design an optimized database design to achieve high speed and performance. This application ...
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1answer
98 views

What index to add in case of join by two optional fields

I have query similar to the one below, it joins two tables by field which can have NULL value. The result matchs the data if both tables have the same data or consider the condition as optional. ...
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1answer
3k views

Mysql 5.5: Optimizing all tables with mysqlcheck - is it useful to run the -check option along with -optimize?

I plan on running 'mysqlcheck --optimize --all-databases' to clear up some fragmentation. Would it be useful to run -check with this option or does the -optimize already take care of that? I am only ...
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2answers
501 views

Slow query with straight_join for small result

I have a performance-problem with a query in my application and I don’t understand the behavior of mysql. The query consists of different joins, especially the join to the mentioncache-table. If the ...
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3answers
191 views

Dog slow query, needs optimizing, please help

I found this query in our web app that has been made by hired programmers. It performs like a dog and needs optimization, but I'm no MySQL wizard (yet), unfortunately. Please help, anything is ...
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1answer
29 views

Why is my Mysql Query verry slow when selecting a text field

i have a problem with a left join. Tables are myisam. Tables CREATE TABLE `article` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `force_startpage` tinyint(1) DEFAULT '0', `title` varchar(255) ...
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1answer
63 views

Help optimizing very slow mySQL query

I have a query which takes about 6 secs to execute. SELECT * FROM (SELECT ord.ID, op.name AS prodName, op.code, ord.date, ord.email, op.total, stat.ID AS statusID, stat.value AS status, ...
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1answer
31 views

Efficient matching rows across two tables with huge data set

I have two tables with about 300+ columns and 20k+ rows each. Each row is characterized by a primary key which both tables have.I have to find the identical rows, rows with changes,and rows without a ...
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1answer
69 views

Optimizing GROUP BY Query

I'm running the following query: SELECT `type`, MAX(`time`) AS `last_updated` FROM `stocks` GROUP BY `type` On the following table: CREATE TABLE `stocks` ( `id` int(11) NOT NULL AUTO_INCREMENT, ...
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1answer
46 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
62 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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1answer
61 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
37 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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1answer
59 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
70 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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1answer
55 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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1answer
34 views

Oracle sql plan for a select with procedure in terms section

Is there any difference in optimizing a plan to execute any sql request in case of using a procedure from a package which checks to display row or not and in case of constructing a plain sql query ...
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2answers
189 views

Which is better? A join or a SELECT IN? [closed]

I have a set of ids that I extract using a join of 2 tables. Now I need some information from 2 other tables. What would normally be the best approach? So a SELECT IN using the set of ids I already ...
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1answer
52 views

strange “using where” in simple query

I have a table with this structure: mysql> describe user_groups; +----------+----------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | ...
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1answer
28 views

Separate table by often changed / not often changed data?

I have a application which querys different gameservers, and stores for example if the server is online, and how many players are connected. But of course there is also data which is changed rarely. ...
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1answer
125 views

Need ideas about OPTIMIZE TABLE

Looking at a database with 10 tables and fairly active at by-the-hour changes. On the first of each month, I purge some rows from 3 tables to remove outdated material and keep the size down. All of ...
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1answer
129 views

Memcache implementation

I have a Wordpress site that uses WP Super Cache plugin in order to make my blog posts and pages stay as HTML so that less PHP/MySQL code is executed. However, there's a featured box that can't get ...
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2answers
132 views

Why does using a variable make a difference in performance?

I have a table that constantly doing insert, and I am trying to run a delete script to remove old record. The delete script looks like this: DECLARE @StarDate DATETIME = '2013-01-13'; DECLARE ...
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1answer
63 views

Faster joining on 'most recent' related rows

I have a bug tracking application. The bug table stores very little, because every state change to a bug happens by adding a comment. For example, the current state of a bug is determined by the state ...
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3answers
707 views

Mysql optimization help

I've tried optimizing mysql as good as I could, but apparently I'm not to good at it :-) So I come to you guys for help. Server specs are: AMD Opteron CPU 8 cores 16 GB RAM 2x2.000 GB HDD 7.200 RPM ...
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1answer
126 views

MySQL query optimization

I'm quite new to big MySQL queries (I used to extract raw data from tables then manipulate them with PHP) so I'd like to know if my query below is too "heavy" or slow for some reason (it seems to be ...
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1answer
89 views

Why searching with $all in Mongodb is FAR SLOWER than the EQUIVALENT search?

$all with only one item is equivalent with normal search right? Here is the log without $all (I used 4700 test cases with 30 thread): Thu Sep 20 17:27:05 [conn11] query newisikotagte15.tablebusiness ...
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0answers
19 views

Should I separate my preferences table?

I have a hobby site where users can find other hobbyists of similar interest. Each user can set a series of preferences that get saved into user_prefs. Right now there are 4 types of preferences, an ...
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1answer
13 views

mysql fulltext query is very slow

I have one table for User detail in MySql with about 500000 records in it. I have also created fulltext index on firstname, lastname field on this table. but when I am trying to search any single ...