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 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 ...
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1answer
551 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
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1answer
352 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 ...
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2answers
868 views

How to improve row estimate of 1 row in join for newly inserted data

A custom statistic exists for the CacheId column of a table. After an overnight statistics update: Statistics for INDEX 'ST_TableName_CacheId'. ...
2
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1answer
319 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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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
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1answer
513 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 ...
2
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1answer
63 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?
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1answer
178 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 ...
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5answers
675 views

Help optimizing query in the MySQL slow-query log

Our database is set up so that we have a credentials table that hold multiple different types of credentials (logins and the like). There's also a credential_pairs table that associates some of these ...
2
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2answers
204 views

In MySQL, should I add an index even if the query that scans the table is only ran once a month?

Concretely, is it worth it to add an index to a query that scans the table of a mysql database, even if that index would only be used once a month? For example, having a users a table and then ...
2
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2answers
95 views

Eliminate duplicates and optimize performance for big count and small LIMIT

I have a big query in my Postgres 9.1 database: SELECT *, count(*) OVER () AS full_count FROM ( SELECT DISTINCT ON(message.messagetime,message.messageid) message.messagetime, ...
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2answers
71 views

Optimizing a MySQL “IN” query

I'm trying to optimize a MySQL table for a query of the form: SELECT Col1, Col2 FROM MyTable WHERE Col3 IN('Val1','Val2','Val3',...) I've added an index to the table: ALTER MyTable ADD ...
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2answers
82 views

Does my table need a primary key and clustered index change?

I have a table holding 1.7 Milion rows. Definition: CREATE TABLE T( [ID] [uniqueidentifier] NOT NULL, [AID] [uniqueidentifier] NOT NULL, [BID] [uniqueidentifier] NOT NULL, [iType] [int] NOT NULL, ...
2
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1answer
172 views

How can I optimize searching a column for a sub-string in SQL Server?

I have a very basic table: CREATE TABLE [obj_local] ( [obj_id] INT NOT NULL, [value] NVARCHAR (1000) NOT NULL ); This table stores a lot of data, and I need to search ...
2
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2answers
1k views

SELECT and UPDATE in a single query while updating selective fields of duplicate records only

I have a MySQL table named Contacts_table with, say, the following contents: ID NUMBER NAME CITY 001 2222222222 John Doe Los Angeles 002 ...
2
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1answer
543 views

Oracle 11g hash join vs nested loops question

I'm using Oracle 11g and working on a legacy system. I have two tables, A and B. A has ~40M rows and B ~4M rows. A has a foreign key on B (B is the parent of A). A query does essentially this: ...
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2answers
187 views

Is it always faster to create indexes after loading data?

I have a large number of records (~1 billion) that I need to load into MongoDB (actually TokuMX, but whatever). I have about 6 different indices I need to create on the collection. Is it always faster ...
2
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1answer
481 views

inserting large quantity of data into mysql table

I need to insert about 400 000 000 rows of test data into the InnoDB table. Table is quite simple: CREATE TABLE IF NOT EXISTS `tgt` ( `id_1` int(10) unsigned NOT NULL, `id_2` int(10) unsigned NOT ...
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, ...
2
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1answer
914 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 ...
2
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1answer
109 views

How is the number of records on a select determined as high or low by optimizer?

What is the threshold between using the index and doing an direct access to the database? I assume this decision is related to the number of index access (and subsequent access to the tables). If this ...
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1answer
1k views

How to optimize a query that includes counts of rows in multiple tables?

My query looks like this: EXPLAIN SELECT ... FROM USER u LEFT OUTER JOIN (SELECT COUNT(*) notified_count, user_id FROM user_email_tracking ON u.id = email_tracking WHERE email_type_id = 4 ...
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2answers
140 views

Optimize query or model, to get an population overview in time

I think I've got a very simple model and query, but I cannot find a way to make use of indexes to boost performance. I wonder if there is a trick in my model, or MySQL query, to speed up the ...
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3answers
2k 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. ...
2
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2answers
342 views

XML Large DataBase is the best? [closed]

Is the best way to implement a large database is XML? Or is there a better way? 1 - reduce the time complexity 2 - Reduce the amount of traffic between the tables And other factors ... Which ...
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2answers
1k 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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1answer
1k views

How to speed up mysql query?

I have query : SELECT `school`.`ARCO_name`, `student-`.`ClassSize_7`, `student-`.`ClassSize_8`, `degree_o`.`degree_code`, `accredit`.`full_faculty_3`, ...
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2answers
1k views

In DB2, how can I disable NLJOIN?

I want to indicate to the optimizer, via SET or optimization profiles, that NLJOIN shouldn't be used at all when optimizing a query. I've been looking for this for a while without any success. I ...
2
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1answer
91 views

Optimize performance for query with CTE using a multicolumn index

I've got this slow query: WITH flks AS (SELECT id FROM public.ja_feedlog WHERE gtime BETWEEN EXTRACT(EPOCH FROM TIMESTAMP '2016-01-24')::BIGINT AND EXTRACT(EPOCH FROM ...
2
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1answer
49 views

Set a filegroup to readonly

I have a set of dimensions which are updated only during specific times. I have moved these tables to a specific filegroup named Dimensions. I wanna keep this filegroup as readonly. When ETL runs, it ...
2
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1answer
64 views

Why is index not used for IN expression with unnested array

I have a query that joins two tables but refuses to use use index unless I add a limit. The case is a bit complicated so best described by showing you. I have two tables, users and ...
2
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1answer
78 views

Would a cron job to automatically optimize tables on a monthly basis be ideal?

I'm wondering if running the OPTIMIZE command via cronjob would be an intelligent move? Sometimes I forget to run optimize for months at a time. My database is frequently using select, insert, ...
2
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1answer
36 views

OFFSET and LIMIT on complex query

I am doing a pretty complex query in Postgres 9.3.4: SELECT p.* FROM unnest('{19082, 19075, 20705, 18328, 19110, 24965, 18329, 27600 , 17804, 20717, 27598, 27599}'::int[]) ...
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1answer
87 views

Slow CREATE TEMPORARY TABLE from SELECT in MySQL

I asked this on StackOverflow, but there are not many hints. So: SHOW CREATE TABLE cashadv_txn: CREATE TABLE `cashadv_txn` ( `txn_id` int(11) NOT NULL AUTO_INCREMENT, `cashadv_id` int(11) NOT ...
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1answer
76 views

MySQL performance problem

I have the following medium size table (less than 3M rows) on a 1 core, 8GB RAM server: +-------------+----------------+------+-----+---------+-------+ | Field | Type | Null | Key | ...
2
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1answer
27 views

what monitor before applying changes on the server? - looking for a basic answer - starting point only

these settings were decision of our development team: there are 2 settings: 1 - max degree of parallelism 2 - optimize for ad hoc workloads On OUR_DEV_SERVER: 1. Run the following script: ...
2
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1answer
51 views

Tuning a query with: index, window function?

Description Environment: Centos 6-x64, Postgres Plus Advanced Server 9.3. I have a table with 4 columns with data as below: id code_id effective_date name 24 12 ...
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1answer
90 views

How to optimize this MySQL query?

Hi can someone help me to optimize this MySQL query, it's taking very long to complete, I have set indexes correctly, but it seems that string operations are slowing this query SELECT ...
2
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2answers
298 views

MySQL JOIN two tables and get latest result

I want to JOIN two tables and get the latest result from each one of those two in a single table. I'm kind of concerned about speed too since tables are growing kinda fast. Close to 60-70k records a ...
2
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2answers
653 views

Slow Performance caused by Correlated Sub-queries & Clustered Index Seek

I'm running a query in which one of the tables (FIELDDATA) has nearly 400,000 records which is taking more than 2 minutes to execute. I ran the execution plan, and noticed that the clustered seek ...
2
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2answers
268 views

How to handle too many inserts?

I have a database that is accessed from remote locations in the world with very long delays and poor transfer speeds. I currently transfer the data using a transaction since either all or no data ...
2
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1answer
715 views

Optimise select distinct from large table

I have a table that contains 320,071,712 number of records, the report that I am currently working on can filter the records by date, after which the number of records come down to 145,878,852. The ...
2
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3answers
214 views

Text Storage and Database Design Optimization in a SQL Server Database

Given a database with a number of columns (c), where some of these columns contain text that is one of multiple values due to a set CONSTRAINT on the columns, what is the most efficient way to ...
2
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1answer
2k views

How to get rid of clustered index scan?

I have a query that was generated by C#/Linq-To-Entities code. As with this kind of query, it looks seriously ugly and I doubt it would help to include it here. But I have run it through a query ...
2
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1answer
906 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 ...
2
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1answer
46 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
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2answers
143 views

Convert to Self JOIN

I have a correlated sub query, which is taking 16 Minutes to execute. How can I convert it to join or optimize it. SELECT SSF.SM_StockCode, SSF.ST_ItemSize FROM Stock AS SSF WHERE ...
2
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2answers
756 views

Setting innodb_buffer_pool_size in for Mysql

We have a dedicated DB box with with 8 GB of RAM and running Redhat linux 64 bit OS. Our MySQL Data + Index size almost 7.8 GB. About setting innodb_buffer_pool_size, I have read 2 suggestions Set ...
2
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1answer
245 views

Why isn't the rows of an EXPLAIN accurate?

I have the following table: mysql> select count(*) from employees; +----------+ | count(*) | +----------+ | 10000 | +----------+ 1 row in set (0.03 sec) I do an EXPLAIN: ...