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

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Optimization of an old query multiple unioned subqueries

I am currently in the process of optimizing a large query that was written for oracle 8i. My company currently uses oracle 10g which gives us a lot of options for optimization. Please Reference the ...
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1answer
62 views

Need to get the first 15 rows from 200k rows of data fast [on hold]

I have 3 tables with a lot of data (each one has 100k rows). I used UNION to get data from that. It takes more than 5 seconds as wait time in server to load the first page. I need only 15 rows from ...
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2answers
62 views

View with left joins are very slow

I have a view based on join of 3 tables and and query on view is taking 10 mins to fetch the results. Can anybody help me in reducing the time taken to fetch results? VIEW CREATE view ...
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2answers
1k views

Oracle query is slower the second time

I have a general question about something I'm seeing in performance tuning in Oracle. I have a query that I'm testing. It's too big and complex for me to provide a simple example, sorry! (I tried ...
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1answer
1k views

statistics State in MySQL Processlist

I have a busy MySQL Server having query SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION ...
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3answers
98 views

Why is my select statement so slow?

SELECT name FROM sys.databases WHERE name not in ('master','model','msdb','tempdb','ReportServer','ReportServerTempDB','1303VISBOC') AND CASE WHEN state_desc = 'ONLINE' THEN ...
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4answers
135 views

Are we a good fit for SQL Server Enterprise and table partitioning?

We currently have a production database that contains millions of records (14 million in the largest table). One function of the database is to provide time sheet information so a single table could ...
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2answers
48 views

Improving `GROUP BY` query performance in sqlite3

I have a little web-application that is using sqlite3 as it's DB (the db is fairly small). Right now, I am generating some content to display using the following query: SELECT dbId, dlState, ...
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1answer
16 views

PostgreSQL - If I run multiple queries concurrently, under what circumstances would I see a speedup? Under what circumstances would I see a slowdown?

I approach you all humbly as one who is NOT a DBA, and I'm sure that my question is fraught with conceptual shortcomings and "it depends on" land mines. I'm also pretty sure that all of you who ...
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1answer
38 views

Last row from a query without Order by

I have something like SELECT var1,var2 FROM table where var3=X AND var4=Y order by var5 desc limit 1; Running this query takes roughly 5 seconds on my database which is far to slow. I was ...
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1answer
41 views

Performance of checking for data in related tables

NB: this question is purely academic / to help improve my understanding of SQL Server performance. Given a master table which relates to one or more other tables, how would you determine the best ...
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1answer
80 views

Best Indexing Strategy for Query with Equality[A], Range[B], Group By[C], AND Order By[count(P)]

I have a poorly performing query: SELECT user_id, count(item_id) as count FROM table items WHERE category = 'magazine' AND created_at > 1384754400 GROUP BY user_id ORDER BY count(item_id) desc ...
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42 views

same query different servers,different execution plan and time

I have this query and it runs less than 2 minutes on Test but on Prod it takes 10 minutes. Both are the same version,CPU,RAM,OS the same. I have four tempdb files on Prod but one one Test. I ...
2
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1answer
67 views

Extremely long query time after upgrading to Postgres 9.3 from 9.1

We're attempting to upgrade from Postgres 9.1 to Postgres 9.3 on a FreeBSD 9.2 zfs box. Performance is noticeably slower across the board, but we have one query that has gone from 353ms to >200000ms. ...
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2answers
80 views

Query Optimization required - Subquery using Inner Join

Could anybody advise how can I optimize this query below please? SELECT IT.[iInternalTransactionID] , IT.[iInternalAccountID] , C.[iContractID] , IT.[dtTransactionDate] AS TransactionDate , ...
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1answer
34 views

Will Rebuild and Reorganize improve Database Migration Script performance execution?

I would like to know if a Database Schema Migration Script (generated by Visual Studio 2008 or greater) will run faster if my target database got indexes rebuilt and/or reorganized. Note: For all ...
3
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3answers
174 views

Nested table as condition prevents using index

The following query joining a subquery does a TABLE ACCESS FULL when the master-table uses nested table as condition. When the condition is a simple =, the same query does an INDEX RANGE SCAN as ...
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2answers
168 views

How can I optimize this query and support multiple SKUs?

My current query only can select one SKU at a time. I can leave salesite_id constant. If there is a way to also have varying salesite_ids that would be good too, but not necessary. Also any ...
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1answer
41 views

A table that consists of multiple FK or creating separate tables for each FK

I have tables called 'books', 'category', 'subcategory', and 'booksCategory'. Each book can have its own category and subcategories. For example, a Sci-Fi book can belong in the 'category' table under ...
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1answer
69 views

How to optimize query

using SQLite3 and the following query, it seems like there should be a better performing way to write this query? Is there? Select Name, Sum(Case When Used Is ...
0
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1answer
47 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
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2answers
28 views

MySQL query performance question

I have a MySQL database where I would like to return results based on multiple rows. id | key | value | selector --------------------------------------------------------- 1 | username ...
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1answer
27 views

Tuning Mongo (TokuMX) for fastest bulk reads

What options do I have for tuning MongoDB / TokuMX for reading the results of queries with large result sets? I'm currently on a single server (no sharding) with the data on an SSD drive. My queries ...
3
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2answers
160 views

Query planner thinks doing a sequential scan on a very large table is faster than using an index?

I've got a query that selects the most favorited photo for each of the last 12 editions for a particular domain (this is just a segment of a larger query, but the problem seems to stem from here): ...
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1answer
19 views

How to optimized mysql query having large dataset

I have two tables in MySql with the following schema, CREATE TABLE `open_log` ( `delivery_id` varchar(30) DEFAULT NULL, `email_id` varchar(50) DEFAULT NULL, `email_activity` varchar(30) DEFAULT ...
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0answers
56 views

A working view now starts timing out

I have 2 identical databases (one larger, one smaller) with identical views. Recently a view on the smaller DB started timing out. Google searches seems to point to deadlocking of some sorts. If I ...
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0answers
20 views

Help with MySQL query which is only occasionally slow? Temp tables/Disc caching?

We have an issue with one particular query whch runs regularly on our MySQL database, though I am not necessarily sure it is a problem with the query itself. 90% of the time it runs perfectly fine ...
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1answer
50 views

How can I control the order of a query regarding to inner join

I have 3 tables. They have table_a 5m records table_b 20m records table_c 20m records I'm performing the query below. SELECT * FROM table_a a INNER JOIN table_b b ON a.a_id = b.a_id AND ...
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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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2answers
182 views

SQL server query is slow *without* including execution plan

I have just set up fresh installation of SQL Server 2012 on a new server and I'm experiencing very strange performance problems. Long story short, for some reason not including execution plan makes my ...
4
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1answer
606 views

Optimising a query against sys.fn_dblog

Looking for assistance improving a query. This query is used to review the last N transactions in the LDF file and then add some useful information like the user, start time, query text, etc.. Here ...
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2answers
182 views

How to fix slow LIMIT queries with big offsets without heavily rewriting them?

Imagine a very basic example of your average discussion board. For example: CREATE TABLE threads ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, title VARCHAR(100), PRIMARY KEY (id) ) CREATE ...
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1answer
99 views

Why is this second query more expensive than the first?

While reading Graph Databases book, I came across this excerpt: I can't figure out why the second query is more expensive than the first. Indeed, both filter on the Bob person. May anyone ...
4
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1answer
116 views

Pull data from multiple tables in a view or function

There are 3 tables from which I need to pull data, and print it in a specific way. http://sqlfiddle.com/#!15/59481/8 You can refer to this question to see how the query was produced. In the fiddle ...
0
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1answer
44 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` ( ...
4
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1answer
522 views

Slow SQL Server query using a DB2 linked server in virtual environment

I have a problem with a slow query which uses a linked server. Let me list out my environment first and I'll get to the issue: Virtual Windows 2003 R2 server (fresh deployments on XenServer 6.1 ...
5
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2answers
1k views

Optimisation of complex query - 100% cost index seek?

I'm a c# developer, however I'm quite experienced with SQL. I have had a bit of experience with optimising queries but I've come up across one that has me stumped. The query takes about 3 minutes to ...
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2answers
111 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 ...
4
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2answers
111 views

Clustered Table Scan Because of “SELECT *”

I have a Records table with over 100 columns and very many rows, and a nonclustered index on 5 fields based on my access paths: CREATE NONCLUSTERED INDEX [IX_Records_CustomerID] ON [dbo].[Records] ( ...
2
votes
1answer
82 views

Select data based on records created_at column

I have two tables Keywords, ProjectReports: http://sqlfiddle.com/#!15/06ae3/1 As you can see in that example everything works fine, but I want to get more data from those 2 tables and I don't know ...
3
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1answer
75 views

Sargable Queries

Very simple question I hope, I'm currently having some scripts I inherited into my project reviewed by the database admins. This has never been done before apparently and lots of issues are being ...
0
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0answers
31 views

Performance getting rows with max column

I have an historic table called 'historic', with three columns: object_id, day, value. For historical reason, day(date) is an integer number (number of day since 01/01/1904) Example: object_id | day ...
0
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1answer
735 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` ...
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1answer
64 views

Couldn't find the long running SQL under v$session_longops

I have following SQL running from a long time. I couldn't see the status When I tried to look the time remaining for the query to complete. Can someone explain me why I couldn't find the SQL status ...
0
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0answers
19 views

Select changes in table by date

I have following table schema name type id int key string count int date date url_id id with example data id key count date url_id 1 system 100 ...
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2answers
93 views

how to solve slow running sub query TSQL

I have a problem with a slow running query. I have analysed the query with the sql server profiler but I can't seem to find a good solution. I did find why it is running slow. If ask the full ...
0
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1answer
56 views

Select from a list of values from JSON encoded data

I have saved the details of the product in JSON format. I am wondering how to select from a list of values from a "JSON_ENCODED DATA" For Example I want to select TV with screen_type as LED or LCD. ...
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1answer
58 views

Improve select query performance

The following select query from my application is taking more than 200ms. The table has around 2 million rows. Is there any ways to improve the performance of this query ? select count(id) from ...
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1answer
101 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 ...
1
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1answer
35 views

Mysql super slow

I have a database of movies that I downloaded, it is around 51mb in size. One of the tables has more than 750k records(all separate insert statements(I believe this is bad)). The rest aren't so bad ...