In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

learn more… | top users | synonyms (1)

3
votes
2answers
522 views

How do I calculate working business minutes?

I'm working on business inteligence reports and one of my task is to create reports for time tracking. I have to report on business minutes (10 hours per day) within business week (monday to ...
3
votes
1answer
23 views

Postgres reduce by key if key is not null

I need to select N rows with seq > X which reduce_key is null and for each row group with the same reduce_key select the one with the biggest seq. Result should be strictly sequential (but with ...
3
votes
3answers
98 views

Having both a integer Primary Key and a GUID/UUID collumn on same table-is this bad

I have my MySQL database having tables where on each table, we have a ID (int,auto increment) Clustered Primary key and a UUID(varchar36) collumn thats just a GUID. The ID is there just for indexing ...
3
votes
1answer
92 views

4m Rows in MySQL, ~5 Minutes to Run Query

I have 2 tables, a users table and a log table which literally logs each time a user signs in. What I'm trying to do is grab a list of all users with a certain rank who have not logged in for over a ...
3
votes
1answer
78 views

MySQL query WHERE IN + ORDER BY, which EXPLAIN is better and how to avoid filesort?

This is my table definition, without any special index for now: CREATE TABLE `filter` ( `field_name` varchar(32) COLLATE utf8_unicode_ci NOT NULL, `category_id` varchar(32) COLLATE ...
3
votes
1answer
76 views

MySQL Filesort/Order By Slow

I've been struggling with a query for the past few weeks and it now just appears as gobbly-gook to me when I try to optimize. The query runs - at about 2.3 seconds, but I know there has to be a more ...
3
votes
1answer
93 views

Improve performance on SQL Server Query

I'm trying to increase the performance of a query and I'm out of ideas: The query does this: gets a 'Process' with specific priorities on selection namely: Picks up a process that has been waiting ...
3
votes
1answer
121 views

Simple SELECT takes forever, but works as a subquery. Why?

I'm running a MySQL 5.1 server and I have a MyISAM table called my_table with nearly 5 million records. Its structure is the following: ...
3
votes
1answer
540 views

mysql: need help to optimize my query/table

I'm wondering if someone could help me optimize my tables/query to speed up a query. It is currently running ridiculously slow. I think a well-thought out index could help me. Any help would be really ...
3
votes
1answer
900 views

Mysql Server optimization tips needed! (InnoDB)

I've recently been trying to optimize our mysql server but I've encountered some pretty serious problems on the way. We're running a game server which is coded in C#. We have two dedicated servers. ...
3
votes
1answer
2k views

Optimizing MySQL for Read-Only?

We have 14 GB worth of CSV's which total 138 million rows. I imported this into a MySQL table first with InnoDB, and then tried again with MyISAM. In both cases, a simple SELECT on primary key ...
3
votes
1answer
115 views

How can I find out which statistics are evaluated by the optimizer?

My enterprise has a farm of many nearly-identical, isolated production environments. Each environment has a SQL Server 2005 database server, each supporting a database with nearly identical schemas. ...
3
votes
1answer
139 views

How to search for an ID and its descendants in this query?

I have the following tables: Project Unit ------------- --------------- ID | IDUnit ID | IdParent I have to select all projects that have the IDUnit ...
3
votes
1answer
2k views

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.* ...
3
votes
1answer
2k views

Why does MySQL use all of memory and goes into swap when doing lots of delayed inserts?

We have a database server running Centos 5.6 64bit 64Gb of RAM. The server is idle most of the time. However, every hour it gets a lot of DELAYED inserts. Up to 3 mil INSERTs per hour into a MyISAM ...
3
votes
1answer
56 views

Optimized MySQL “optional” FULLTEXT search on multiple tables

I need to select data with optional columns in where clause based on client input. my query is like this: SELECT a.id, a.title, b.txt AS b_txt, c.txt AS c_txt FROM a LEFT JOIN b ON a.b_id=b.id ...
3
votes
0answers
156 views

Form builder schema for SQL database?

There are many ways one can envision the solution, from the top of my head: Two table approach: Field table with (name, field_name, type, description, meta) attributes Form table with (name, ...
3
votes
0answers
94 views

Why the stored procedure is much slower than a temporary table? [closed]

I want to do the updating of my database every day and I will like to use stored procedures but the time of execution of the temporary table is faster than the stored procedure. How can I optimize my ...
3
votes
0answers
317 views

Slow transactions, many locks

At high load conditions the server app stops responding to client because begin/commit statements are executing very slowly (some take 15 seconds). The queries are simple - insert, update two columns ...
3
votes
1answer
142 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 ...
3
votes
0answers
69 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 ...
3
votes
1answer
2k views

Mysql - show results from 3 tables excluding NULL or EMPTY values for certain fields

I have 3 simple tables with polls, users and votes. I'd like to show all polls ordered by clean count of votes (sometimes either poll_id or user_id don't get inserted). Furthermore I'd like to show ...
3
votes
2answers
240 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
2
votes
2answers
317 views

Why the WHERE clause is not pushed down in the view's query?

With Postgres 9.4, I'm doing the following query quite often: SELECT DISTINCT ON(recipient) * FROM messages LEFT JOIN identities ON messages.recipient = identities.name WHERE timestamp BETWEEN timeA ...
2
votes
1answer
297 views

Help required with query (join) optimization

I am working with a fact table source query and I have observed that performance of the query is pathetic. It has increased from 1:00 min to 6:30 min by just using a function in the select clause ...
2
votes
2answers
690 views

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 ...
2
votes
1answer
5k views

Why isn't oracle using an index for distinct query ?

This is the scenario SQL> exec dbms_stats.gather_table_stats(user,'TM', cascade=>true) PL/SQL procedure successfully completed. SQL> SELECT SEGMENT_NAME , SEGMENT_TYPE , BYTES / 1024 / ...
2
votes
2answers
318 views

Why does adding LIMIT to my query make it crawl?

Simple query: select sum(score) total,name,gender,dob,country from users join scores on users.id = scores.user_id where date between '2012-01-01' and '2012-01-31 23:59:59' group by scores.user_id ...
2
votes
3answers
12k views

Is there any command to optimize all MySQL tables one by one automatically?

I execute below command line statement to optimize a table: optimize table tablename; Is there any command or statement which can optimize all the tables one by one of the selected database?
2
votes
1answer
3k views

Will OPTIMIZE TABLE have any impact on my data?

I'm having issues with a database that is getting quite slow. The analyzer in phpMyAdmin recommends that I run OPTIMIZE TABLE on my tables. But before doing so, I would (of course) like to know if ...
2
votes
1answer
103 views

Understanding performance of highly unique WHERE clauses

I've been struggling to understand how to deal with a specific type of performance issue that shows up very often in this scenario: when you are wanting to apply multiple filters in a query, but you ...
2
votes
1answer
74 views

How to tune the query on all_constraints in Oracle 12c?

How to tune the following query, as it's taking around 8 seconds: select constraint_name,table_name from all_constraints where r_constraint_name in ...
2
votes
2answers
278 views

Changing ORDER BY direction causes performance issue

I use MySQL 5.6, and I have two tables each with 16M rows: CREATE TABLE IF NOT EXISTS `newsstudios` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(255) COLLATE utf8_unicode_ci NOT NULL, ...
2
votes
2answers
1k views

Trying to optimize query for performance (MySQL)

So I have this table that has a lot of foreign keys but when I will a record, I need to join all on those tables because I generally need those fields for the record to make any sense. The basic ...
2
votes
2answers
66 views

Retrieving changed rows only from a table with 10^7 rows

I have a table with about 300 columns and about 107 rows and I have to retrieve changed rows only, ordered by time (not distinct, but changed). The result set may be limited to 100 rows as well. I've ...
2
votes
2answers
54 views

Optimizing query using a WHILE statement

I'm trying to convert a view that extracts a yearly amount into something more WHILEish The query is more or less: SELECT * FROM (SELECT SUM(EmployeePaid)*2 AS Total2013 FROM TblRecords WHERE FYear ...
2
votes
1answer
165 views

Threshold for sort spill and random cardinality estimates

I wanted to test tempdb spill warnings so I run the following script on SQL Server 2014: USE tempdb IF OBJECT_ID('tempdb..tblTest') IS NOT NULL DROP TABLE tblTest CREATE TABLE tblTest ( ...
2
votes
1answer
47 views

Convert Log table days in a state

This is simplified but represents the problem I am trying to solve. We have a table containing 5-10 million rows in a format similar to the following... Input Table Date Item Moved to Box Oct-1 ...
2
votes
2answers
3k views

MySQL / InnoDB: Does daily optimization improve performance?

Would performing daily optimizations of tables increase performance for MySQL and InnoDB? I have never did this before, but I have seen this module for Drupal http://drupal.org/project/db_maintenance, ...
2
votes
1answer
3k views

How to improve MySQL Server Performance..??

As a MySQL DBA most of the times we are supposed to optimize a poorly performing MySQL Servers. Now my question is where to start from like we will need to find out many things as 1.Find the ...
2
votes
1answer
4k views

16 Cores 12 GB RAM server MySql Configuration - my.cnf

The server takes 20+ seconds (wait time/slow IO response time) to response to a HTTP request even with memcached and APC installed. I believe this has something to do with MYSQL since the site as lots ...
2
votes
1answer
33 views

How to optimize this query on Postgres

I'm trying to make a relatively simple query, but it's taking much longer than I'd expect. I have an index in place, but it doesn't seem to be helping much. Here's the query. It sometimes takes up to ...
2
votes
1answer
63 views

Why OUTER APPLY forces scanning the entire table?

I have a query which does not performs well and optimizer scans all 108864 items from table ExternFile uselessly when seeking only 30 rows would be fine. I have simplified the problem to following ...
2
votes
2answers
233 views

MySQL taking too much CPU

Below is my .cnf file and if I see my CPU consumption 99.99% of it my the mysqld commands. The MySQL server is connected from remote machines that update data in it frequently, but I make sure that ...
2
votes
1answer
479 views

Optimize Percona MySQL InnoDB 3.2TB database

(Before you will call me an idiot or start laughing, please remember it's a real deal on my side and I cannot cancel this assignment as it is a part of a bigger project) I have a database server that ...
2
votes
1answer
279 views

Is there a negative effect if I place an index on every column in a wide table?

We have a wide dataset that isn't very tall (say 250K rows, 90 columns). We will be providing users with an interface that allows them to generate arbitrary queries against this dataset. They can ...
2
votes
1answer
298 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, ...
2
votes
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 ...
2
votes
1answer
61 views

Is there any way to get the optimization time in MySQL?

I'd like to see the time optimizer takes to optimize a query. Is there any way to get that time?
2
votes
1answer
166 views

How to know what to investigate and how for a VERY slow stored procedure

I have inherited a large and slow stored procedure and it's giving me a nightmare: I'm not a DBA, although I have some knowledge, but I don't know where to start to identify this bottleneck. I have ...