A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.

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1
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2answers
194 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
7
votes
2answers
79 views

SARG cardinality estimate, why not full-scan?

Why there is no full-scan (On SQL 2008 R2 and 2012)? Test data: DROP TABLE dbo.TestTable GO CREATE TABLE dbo.TestTable ( TestTableID INT IDENTITY PRIMARY KEY, VeryRandomText VarChar(50), ...
1
vote
1answer
35 views

Update records from one table to another in different databases where condition is accomplish

I have two tables stored in two differents DBs and I need to perform some sync between both tables based on lastmodifieddate and lastSyncAt. Let's call them as db1 and db2. This is the DDL schema for ...
3
votes
3answers
263 views

Slow SQL Server authentication, but fast SAN, fast querying?

I am asking you after days of research but I think I don't have required skills to understand what is happening. I have a slow authentication on a SQL Server 2008R2, which leads to a timeout for the ...
5
votes
3answers
157 views

Postgres is performing sequential scan instead of index scan

I have a table with about 10 million rows in it and an index on a date field. When I try and extract the unique values of the indexed field Postgres runs a sequential scan even though the result set ...
1
vote
1answer
382 views

MySQL: Optimize query with a range and distinct count

I have a query on a large table with millions of rows that looks like this: SELECT COUNT( DISTINCT clicks.tx_id ) AS unique_clicks_count , clicks.offer_id FROM clicks WHERE ...
0
votes
2answers
58 views

Minimizing SELECT latency in PostgreSQL

I am evaluating Postgres 9.4 performance on a machine with Intel i7 quad-core 3.6 GHz CPU, 8 GB ram, and 7400 rpm HDD (no RAID) running Linux Mint. The DB schema has the following table: ...
3
votes
4answers
537 views

Is database partitioning for performance reasons meaningful in a virtualized environment?

When running SQL server on physical hardware, placing database data and log files on separate disks or RAID arrays can benefit performance, resilience, and maintenance. Partitioning the database over ...
1
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0answers
29 views

Select SQL_Calc_Found_Rows query extremely slow

I'm Wordpress 4.2.2 on an Ubuntu 14.04 LTS server, with PHP 5.9x and MariaDB 10.0.17. When clicking on a post on my site I see many slow queries that all resemble this and it ends up taking as 8 or 9 ...
1
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2answers
32 views

Reorganize Index Task [closed]

Can the Reorganize Index task (maintenance plan or SSIS package) be used to tune performance? Is this an adequate step of triage for degraded application/query performance?
1
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2answers
2k views

Improve MySQL Query Performance - Too many records

I am using MySQL RDMS for a contact management system. Now a days my database grew in size and contains more than 1 million records. Checking duplicate phone numbers became a big issue during ...
1
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1answer
34 views

Statistics needs to be captured for query analysis

What statistics are required to theoretically prove that X query work better than Y query. As per my knowledge I need to look for: Query elapsed time Logical read Logical write Physical read ...
2
votes
1answer
135 views

Minimizing Page Fetches

I have a complicated database structure and am trying to use it to retrieve Records based on multiple selection criteria from several tables. As a general rule, is it better to attempt to use ...
4
votes
0answers
87 views

Why is query thousands of times slower with DESC?

I have a PostgreSQL database (AWS RDS) and ran the following queries in psql: livenet=> EXPLAIN ANALYZE SELECT * FROM outputs ORDER BY height LIMIT 10; Limit (cost=0.57..36.82 rows=10 ...
0
votes
0answers
194 views

How to load XML data into an oracle db table?

Is there a way to load the XML format data into an Oracle 11g DB table directly ? Can we write a stored procedure to accomplish the same in a more efficient way with the best performance? Can we ...
9
votes
2answers
99 views

Why isn't the primary (clustered) key being used in this query?

I have a SQL Server 2008 R2 table whose schema structure looks as follows: CREATE TABLE [dbo].[CDSIM_BE] ( [ID] [bigint] NOT NULL, [EquipmentID] [varchar](50) NOT NULL, [SerialNumber] ...
1
vote
1answer
129 views

Rerunning query in the same connection takes significantly longer

I am having a weird issue when a running a query that joins some semi-large tables (one table is about 2 million rows and the other about 21 million) together. What happens is the query does not run ...
0
votes
1answer
182 views

How can I optimize this Cross Table COUNT() mysql query?

I am trying to cut down the retrieval speed of this MySQL query. All instances of COUNT() point to the PRIMARY key of each field. Currently this query makes my MySQL hang. It seems ridiculous as I'm ...
0
votes
0answers
31 views

Create table with select Query on DB link

I'm trying to execute the following query, it is taking more than usual time. I'm retrieving data from db link. Without the create table statement the query is giving results. For Create table also if ...
-3
votes
3answers
197 views

SQL Server - Transaction Slowness [closed]

I'm seeing some behavior right now in SQL Server 2008 R2, and I can't decide if the server is underperforming or not. I've set up a test to insert an integer into a table, as defined below, 75,000 ...
0
votes
1answer
109 views

Query causing Database lock problem (php/Mysql) [closed]

What is the issue with my query? When I execute, it lock the database for 5 to 10 minutes. Please help me to optimize this query. SELECT u.username, u.email, u.created_at, ...
1
vote
1answer
121 views

A single, simple update takes 10+ seconds

We are running MySQL 5.1.71-log and have a table with 2.7 million rows. Simple updates to it are regularly taking more than 10 seconds to execute. The table structure is: CREATE TABLE `person` ( ...
0
votes
2answers
3k views

Optimize IN clause in where query with order by - MySQL

I am trying to optimize a query that using IN clause in WHERE to avoid file sorting. To make it easy , I created the following sample which shows the problem. Here is my query: SELECT * FROM `test` ...
0
votes
0answers
70 views

Need your help in query tuning

I read ​one article which shows how to use different aggregations effectively. http://sqlblog.com/blogs/paul_white/archive/2011/12/04/is-distinct-aggregation-still-considered-harmful.aspx I am ...
2
votes
1answer
39 views

How do I prevent my query from needlessly generating rows it'll throw away later?

I have the following query: SELECT stream_points.time AS point_time, stream_points.value AS point_value, stream_predictions.value AS prediction_value, ...
4
votes
1answer
90 views

Should I use a subquery to help SQL Server find the correct plan

I have a query (which has components which are built on the fly depending on the selections a user makes in the interface) that runs in SQL Server 2008-R2 that runs in about 100 databases. Users are ...
2
votes
1answer
58 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 ...
1
vote
1answer
398 views

SQL Server 2012 Performance Test

I've been given a task to test where an SQL Server 2012 can achieve better performances - we have two options: Use the SQL Server as an On-Premise machine (Standalone server that we have) Use the ...
2
votes
1answer
68 views

Mongodb high lock percentage / slow queries

I'm working with an application using MongoDB that is getting a fairly large number of incoming requests and I've noticed that the responses are getting slower as the number of requests get higher. ...
6
votes
4answers
41k views

High CPU usage on SQL server - Slow queries [closed]

Our MS SQL Server is using about 95% of the CPU-power. After a server (hardware) restart, or a SQL-Service restart, the usage is 0% and slowly increases over the course of 1-3 days. Depending on how ...
1
vote
2answers
73 views

Is there's another function to optimize this query in MySQL?

I want to use a function that returns for me the same result in one line is that's possible?? MIN( CASE WHEN (data.pro LIKE '1 %' ) THEN 1 WHEN (data.pro LIKE '2 %' ) THEN 2 ...
1
vote
1answer
41 views

Why is MariaDB 10 refusing to use my index on a date field?

I have the following table definition: CREATE TABLE `bets` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `id_mp` bigint(20) NOT NULL DEFAULT '0', `coin` char(3) COLLATE utf8_unicode_ci NOT NULL, ...
0
votes
1answer
133 views

Tuning Mysql and Monitoring

I would like to know if anybody can point me towards a tool/way for MySQL database tuning ... Actualy the tunning of my.cnf is like below My database is in MyISAM | Mysql 5.1.73 key_buffer = 500M ...
0
votes
0answers
45 views

PostgreSQL query taking a long time

I have a query that is taking hours to run. There is a large table to parse, is there any way to optimise this? with VehData as ( SELECT * from dblink('host=databasesrv port=1234 ...
0
votes
2answers
265 views

Database is slow once in a while

I am executing a web service for 100 times. The average response time of this service is 1.5 seconds. But when I look at the response time of each execution individually, there are a few executions ...
1
vote
1answer
59 views

Why isn't Postgres doing an index-only scan?

I am using Postgres 9.4. This is my table: id | integer | not null default nextval('frontend_prescription_id_seq'::regclass) presentation_code | character varying(15) ...
5
votes
1answer
306 views

Grant users privilege to use QUERYTRACEON 9481

Microsoft suggests using OPTION (QUERYTRACEON 9481) for queries that have "degraded" performance against SQL Server 2014 databases running under compatibility level 120. In my situation, "degraded" ...
3
votes
1answer
47 views

Why is the secondary selective index not used when the where clause filters on `value()`?

Setup: create table dbo.T ( ID int identity primary key, XMLDoc xml not null ); insert into dbo.T(XMLDoc) select ( select N.Number for xml path(''), type ) from ( ...
3
votes
3answers
71 views

Is it better to create another table to possible null values in relational databases?

I'm designing a relational database to use in MySQL. I have the next situation: In one table there are fields that in the most of situations are NULL. The fields would be like: Table name: tabla ...
1
vote
0answers
49 views

Query execution taking long time

SELECT sqltext.TEXT, req.session_id, req.status, req.command, req.cpu_time, req.total_elapsed_time FROM sys.dm_exec_requests req CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext select ...
1
vote
0answers
24 views

Delete using join or using sub-query?

I need to delete rows from a table based on what is present in a temporary table. For me, both of these statements work : DELETE from main_table where `id` in (select `deletable_id` from ...
17
votes
2answers
6k views

Stored procedures vs. inline SQL

I know stored procedures are more efficient through the execution path (than the inline sql in applications). However, when pressed, I'm not super knowlegeable about why. I'd like to know the ...
3
votes
3answers
144 views

Optimizing a query which runs through all hours in a day

I need help optimizing a query. I'm using PostgreSQL 9.3.4 currently but can upgrade to 9.4 if needed. I have a table with 60+ millions of records which looks like this: ...
4
votes
0answers
42 views

6GB Table - 37Mi Rows - 'System.OutOfMemoryException' - SQL 2008 R2

I have a proc, looping through databases( the insert is in a fix database...the select uses the loop ), making inserts (Will hide names for security): insert into Main_Database..Table(16 Fields) ...
1
vote
2answers
160 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 ...
1
vote
2answers
63 views

Is LIMIT processed before or after retrieving data?

MySQL. My heavy query crashed our MySQL server. If I add LIMIT 10 will it make my query more lightweight? (both for indexed and unindexed queries). Which way LIMIT are processed: before the rest of ...
0
votes
1answer
175 views

MySql: Slow join and group by on indexed columns

The following query takes 15-20s to run SELECT "Trade_US"."ID" AS "Trade_US.ID", "Server_US"."Name" AS "Server_US.Name", "Trade_US"."TradeTypeID" AS "Trade_US.TradeTypeID", "Users"."ID" AS ...
0
votes
1answer
119 views

Complicated data

I have a requirement i got from my father. He gave me a table and wanted me to digitalis it. So that he can the system can do all the dirty jobs for him ( that's why there are developers in the world, ...
1
vote
3answers
92 views

Index optimization and cardinality

I'm by no means a DBA expert. Rather, a Magento developer having to troubleshoot some slow queries. I'll jump right in -- here's my attempt to EXPLAIN the troublesome query: EXPLAIN SELECT ...
1
vote
1answer
301 views

MySQL: COLLATE performance

I have a table called users with a column firstname and with collation utf8_bin I want to know what happens under the hood when I execute an query like: SELECT * FROM `users` `a` WHERE ...