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

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0
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1answer
86 views

How to optimize query?

I need to optimize the following query: SELECT DISTINCT column1, column2 FROM tbl_name WHERE column3 = 'x' AND TRIM(UPPER(column4)) = TRIM(UPPER('y')) AND TRIM(UPPER(column5)) = ...
1
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0answers
140 views

Mysql key_buffer_size already 16GB but some fulltext searches are still slow

I have a query w/ full text search which takes 5 - 10 secs. key_buffer_size is already 16GB. Table has 15 million records and has a compound fulltext index on fields: categories and company. Table ...
2
votes
2answers
443 views

Improve CTE performance

is there a way to improve the performance of a recursive CTE like below, I am unsure if I can add indexes on joins when the joins are using ROW_NUMBER? DECLARE @File_Name VARCHAR(8000), @Disk ...
1
vote
1answer
575 views

Would adding indexes to my foreign keys improve performance on this MySQL query?

Consider the following query: SELECT `locations`.`id` AS `location_id`, `locations`.`address`, `locations`.`lat`, `locations`.`lng`, `tickets`.`status_id`, `customers`.`name`, ...
2
votes
2answers
5k views

Get username and/or IP address responsible for a query

I use the following query to find performance improvements in queries: SELECT TOP 20 SUBSTRING(qt.text, (qs.statement_start_offset/2)+1, ((CASE qs.statement_end_offset WHEN -1 THEN ...
4
votes
1answer
225 views

What is the name of this type of query, and what is an efficient example?

The purpose is to find a parent, given it's children. For example, say you have a marketing package (aka a "combo"), and want to match it based on the products in it. Example table/data: create table ...
4
votes
1answer
1k views

How to properly index hstore tags column to faster search for keys

I imported a large area of OpenStreetMap's planet.osm file into a postgresql database. The database contains a table called nodes. Each node has a geometry column called geom and a hstore column ...
1
vote
2answers
571 views

Obvious inefficiencies in this Netezza query?

Why might this query be taking nearly 2 hours to run when similar queries complete within a minute? CREATE TABLE T3 AS SELECT A.*, COALESCE(C.FIELD1,0) AS FIELD1A, ...
0
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1answer
955 views

Speeding up MySQL NOT IN (Subquery) [duplicate]

I'm currently up to try to improve the performance of some of my queries. As far as I know, statements like "IN" or "NOT IN" are even faster with a large amount of values if a subquery on an indexed ...
-1
votes
1answer
117 views

Query performance in SQL Server [closed]

What factors should I check when I compare the performance of a query? I saw many articles stating about IO cost, subtree cost (by using Execution plans), statistics such as CPU time, elapsed time ...
2
votes
2answers
218 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, ...
0
votes
2answers
87 views

Query performance differs greatly between a development setup and production

I'll try to keep this question straightforward, though I am dealing with a big ball of mud. When I run my test query acrossed linked servers both located locally (on a shared virtual host), the ...
-1
votes
2answers
4k views

Query to search for a substring in xml

I use below query to search for a substring in whole xml(including node name and node value) SELECT * FROM tablename WHERE ( Charindex('abc',CAST([xmlcolumn] AS VARCHAR(MAX)))>0 ) I want an ...
7
votes
1answer
1k views

Estimated vs Actual rows differences (actual much smaller than estimated) - sort

I'm running a query that is processing some nodes out of an XML document. My estimated subtree cost is in the millions and it seems it all comes from a sort operation sql server is performing on some ...
0
votes
2answers
854 views

Update performance: clustered versus covering index

I have a simple, 3-column table with about 50 million rows in it. This table gets about 5,000 inserts/updates per second, and perhaps 20 queries per second are executed against the table. The table ...
1
vote
1answer
640 views

Is it possible to avoid filesort?

Is it possible to avoid 'Using temporary' and 'Using filesort' for the following SELECT query? I can't figure out a way to do it. I tried adding indexes, for both top_expire and program, but didn't ...
15
votes
1answer
3k 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 ...
5
votes
4answers
24k 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 ...
0
votes
1answer
495 views

Filtering records not present with specific conditions in another table

I have a table (let's call it extra_info) in MySQL that has various extra infomation/labels on user accounts: account_id / data_key 11 / 'test' 11 / 'blah' 12 / 'coupon a' 12 / 'coupon b' 15 / ...
0
votes
0answers
58 views

Faster way to GROUP or ORDER dynamic fields?

We have this query in our app, that searches a table for a song title using MATCH AGAINST and picks the most relevant results. The table has around a million results and is growing. The app has been ...
1
vote
2answers
183 views

Prune unused joins

I have expected that selecting from a view would not join the tables from which I don't query any values, but it doesn't seem to be the case. I have a bunch of tables with the following structure: ...
3
votes
2answers
6k views

SQL SERVER - Linked Server and query performance

I have a performance problem related to SQL Server/linked servers/views. I hope you can help me understand what is the best way to do what I want =). I have a database K with 3 linked servers ...
7
votes
1answer
1k views

Algorithm for finding the longest prefix

I have two tables. First one is a table with prefixes code name price 343 ek1 10 3435 nt 4 3432 ek2 2 Second is call records with phone numbers number time 834353212 10 ...
0
votes
2answers
218 views

How can I increase performance for select in select statement

The item table is like this id category_id name registered I have to show total number of items from the beginning. Suppose between 2013-05-01 to 20-05--05, I have to count all the items ...
-1
votes
4answers
141 views

Dropping and recreating indexes [closed]

I most often come in a situation where the users move there database from one server to another and immediately after they move they face performance problems(slowness). I somehow manage to rebuild ...
0
votes
0answers
505 views

Properly index magento mysql tables to improve specific query performance

I am running magento community edition and its db performance is horrible. I have the following query: SELECT `width_idx`.`value`, COUNT(DISTINCT width_idx.entity_id) AS `count` FROM ...
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votes
1answer
1k views

what's the fastest method to export a table through sql query ? 11g - performance

I'm connected to the oracle server remotely. I need to export a table data(the whole table) with millions of records but due the hosting restrictions I can only use SQL (no exp , expdp) . Therefore ...
1
vote
3answers
2k views

How do I use subquery on the same table in MySQL?

I have a query like this which takes a really long time to run. The table is around 4 million rows. DELETE FROM TABLE WHERE value_was IS NULL OR value_was <= value_now; I'm hoping I could ...
3
votes
3answers
143 views

How can I improve this query?

About a year back I introduced a query which returns a sort of "Customers Also Purchased" data-set. At the time it ran reasonably fast however, as of late it's become very slow, sometimes taking up to ...
0
votes
2answers
479 views

how to find similar word with more similarities

how to Find words with length less than or equal... declare @inp nvarchar(max),@data nvarchar(max) set @inp='You can dance, you can jive, having .... jove... jve, ...' set @data = 'jeve' ...
0
votes
2answers
943 views

How to use and optimize subquery on 100 million rows

What I'm trying to do is running a job on more than 100 million domains which haven't processed before. I have two tables, "domain" and "domain_setting", on every batch (10.000 domains per batch) I'm ...
2
votes
2answers
1k views

Is there a difference in performance between @date and getdate()?

Usually I use the getdate() function in my where clauses to go back in time. Something like: DOC.DATUM >= DATEADD(DD,-1*SSN_SDO.DANA_ZA_POVRAT,GETDATE()) Will SQL Server 2008R2 perform faster ...
2
votes
4answers
5k views

How can I query data from a linked server, and pass it parameters to filter by?

I have a really big query that needs to be run on multiple databases, and the results appended to a temp table and returned. The basic syntax looks something like this: INSERT INTO #tmpTable (Id, ...
1
vote
1answer
77 views

Query optimization when no row is returned

I am using explain to figure out what is happening in my query which is: explain select t from c where u1_id = 1 group by t; I see "Using where" in the Extra column of the resultset. But this only ...
0
votes
1answer
49 views

Optimizing Query

Can anyone help me tuning this query..... explain extended SELECT DISTINCT a.msisdn FROM `std_msc_opr_wise` a LEFT OUTER JOIN (SELECT msisdn FROM as_treat_pre_usage_30days GROUP BY ...
0
votes
1answer
125 views

What is the correct model for related tables with millions of rows?

I need to create a question and answer tables that will have millions (maybe billions) of rows. The current model is: Question Table id_question (PK, auto increment) id_user question_content ...
0
votes
0answers
436 views

SQL nested select (query rows after variable), running slow

Have large table (Sybase) rows = 6276225. I'm pulling call status and my query is very slow. In effect what I’m trying to do is pull data for any event after my variable. While querying for just one ...
0
votes
1answer
297 views

MySQL stored routine performance while using PREPARE

Instead of maintaining stored routines for each database in my current environment I have decided to create separate database just for stored routines storage. Mainly I am using them for reporting. ...
0
votes
1answer
28 views

Simple query not using indexes

My query is not using indexes. It is a simple query. Can someone explain why that's the case? The query: select TIME_FORMAT(start_time,'%H:%i') start_time, TIME_FORMAT(end_time,'%H:%i') ...
2
votes
2answers
146 views

Different queries result in big difference in performance

I have 2 similar functions, different way result in big diff in performance. The PostgreSQL version: 9.2.1. Function 1 create or replace function func_1() returns text as $$ declare v_i ...
0
votes
1answer
874 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 ...
4
votes
3answers
2k views

Query runs slow in test site on first execution. Why?

I found this query by watching a test site with sql profiler for anything taking over 10 seconds. I plopped the code right out of sql profiler and into sql studio, where it was able to execute ...
4
votes
2answers
3k views

Is high Extent Fragmentation a problem?

DBCC SHOWCONTIG scanning 'MyTable' table... Table: 'MyTable' (2048062382); index ID: 1, database ID: 28 TABLE level scan performed. - Pages Scanned................................: 1019182 - Extents ...
5
votes
1answer
461 views

How does order of index affect performance in SQL Server?

I am wondering how does order of index affect performance (ASC, DESC) ? If it affects, why ? And which order should I choose ?
0
votes
1answer
283 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 ...
0
votes
0answers
114 views

Identical Postgres index scan taking 5x longer on server

I have an intermediate table for managing a many-to-many relation between tables called Expert and Subject: Column | Type | Modifiers ...
0
votes
1answer
99 views

speeding up a query on MySql [closed]

I have a table with more than 10 million rows and 10 fields(columns). There is an index on field_1 and I am running the following query. create table t2 select field_1, sum(ifnull(field_2,0)) ...
5
votes
1answer
3k views

Could too many idle connections affect PostgreSQL 9.2 performance?

Some queries on my database server seem to take a long time to respond, and I believe the CPU usage is high. When running ps aux, I see ~250 "idle" connections (which I believe to be too many). I ...
7
votes
1answer
16k views

How to speed up queries on a large 220 million rows table (9 gig data)?

The issue: We have a social site where members can rate each other for compatibility or matching. This user_match_ratings table contains over 220 million rows (9 gig data or almost 20 gig in ...
6
votes
2answers
314 views

Postgres performance difference on insert

I was tried to partition one large table, and come with such Postgres behavior that I could not explain. Maybe you will have any suggestions? I went quite straight forward way (i know that it is not ...