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

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90 views

SQL execution 2 seconds with LIMIT parameter, without only 0.2s why?

This is my query and I need to return only 12 rows, but it takes 2 seconds with parameter LIMIT 12 while it takes only <0.2 to process all ~600 results (without LIMIT 12 or with LIMIT 1200 for ...
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46 views

Table design for optimum performance

For example let's say I have to create a table called Employee with columns EmployeeID, Name, DOB, Address, DepartmentID[FK]. So I create the table as follows with a primary key and a nonclustered ...
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33 views

Table maintenance after dump/source

I just completed a major DB migration, all went well. I had a 450 GB DB on old underpowered windows hardware using MySQL 5.0 and I moved everything to much more powerful (512gb memory, server 2012) ...
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84 views

Performance tuning self-joining MySQL query

I asked a question recently on the correct way to update a table using multiple joins to itself in order to generate the desired values. Updating MySQL innodb table based on multiple joins After ...
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42 views

Billion records mysql performance with large result sets

I'm currently developing an application which will have several mysql tables where 3 of them have very large amounts of records. The thing is that my app will have to sync each account on a hourly ...
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26 views

Intermittent MySQL 5.17 issues - extremely slow queries

I am experiencing major issues with intermittent mySQL issues. To give some background the website runs optimally for the majority of the time, however 3-4 times a day queries that should take a split ...
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33 views

database design - upvotes for various types

In the early stages of an application I'm developing, I had two relatively simple tables - one for content and one for upvotes. The content table's schema is as roughly: data | text id | integer ...
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12 views

first query on my table takes apx: 0 sec but taking too much time on or after 3 to 4 query

I have the following table in mysql database: CREATE TABLE `chronologicallists` ( `sno` int(250) NOT NULL AUTO_INCREMENT, `empSno` int(11) NOT NULL COMMENT 'Employee Serial Number', ...
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64 views

Oracle 11 express vs Oracle 11 enterprise performance

We have a very long select query which is executed via our java application through hibernate. This takes 2 seconds to execute on our local Oracle 11 express db server and takes around 22 seconds on ...
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35 views

SQLServer dependency graph and performance

I have a large stored procedure running on SQLServer2008 to produce a report on the previous day's data. It rehashes data from 12 tables, including a lot of ORDER by date and CASTS. Among others, it ...
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2answers
84 views

Identical Servers but different query execution plans [duplicate]

We have two server with identical hardware configuration and SQL server configuration. The only difference in the server's being: Server SQL1 - 256 GB RAM Server SQL2 - 128 GB RAM The same database ...
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30 views

How to handle too many instances of multiple tables?

If there is a table accessed by multiple DB threads ( for example 100) at a time then how many instances of that table will be opened? If I run show open tables and see that in_use column value of a ...
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1answer
90 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 ...
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33 views

How does indexes work on an Access query

I'm working on an Access 97 Db and I'm trying to speed up some low performance issues, as of right now I'm wondering how indexes works in Access. Using this table with 300k rows i get awful results ...
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15 views

Design and queries for analysis of event-sequences

I will have to store sequences of events with certain properties in a database (MariaDB preferably) and I have some issues regarding the design and queries. The crucial part is the analysis of the ...
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1answer
92 views

SQL Server sometimes uses a lot more cpu for query

I have a stored procedure with a quite heavy SELECT statement that includes five joins and uses FieldName LIKE '%searchterm%' on multiple columns. This query usually finishes in about 2-5 seconds. But ...
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1answer
42 views

Slow response from SELECT query

I have 50 lac rows (i.e. 5 million rows) in student table. I fire select * from student where s_name like('%something word%') limit 0,5. I define indexing on s_name column. That query takes 2 ...
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78 views

My Query is waiting on “db file sequential read” for 5 minutes and getting timeout after that in Oracle

I have a very simple query when I run it individually from the SQL developer in my oracle database it is running perfectly, but when it is part of application flow then it is failing with timeout and ...
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19 views

mysql update a table from another table - performance

I have two mysql tables, table_A = 2500000+ (rows) table_B = 6000000+ (rows) I need to update rows in table_A from data in table_B (using a multithreaded application) What is the fastest way ...
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1answer
96 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, ...
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40 views

Query being executed beyond timeout in a transaction Oracle

I have a simple query as below when executed separately the result is coming very quickly. But when is part of the application flow the same query is being shown as in execution status for more than 5 ...
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0answers
47 views

Slow mysql UPDATE with IF() conditions

not sure why I can't even EXPLAIN this query. Mysql refuses to EXPLAIN it. Table contains a million meaningless test entries. Full schema and data dump of the table available here: ...
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0answers
117 views

Memory Issue - SQL Server 2008r2

I am trying to troubleshoot a memory issue on a 2008r2 instance. Very high resource semaphore waits are present and a general slowdown of queries,backups,dbcc checks. Only one instance of SQL Server ...
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39 views

Speed up sorting in this query

I'm trying to optimize the following plan and noticed that PostgreSQL spends a lot of time (relatively speaking) on sorting before the merge joins. Is there a way (using indexes, cluster the table, ...
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0answers
25 views

DB2 LUW 9.5 ignoring indexes

I am seeing something in DB2 that I've never seen before. DB2_VERSION: 09.05.5 AIX VERSION: 7.1.0.0 I've got a query that is properly indexed. In fact, it’s heavily indexed. However, when I get the ...
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1answer
25 views

Can having a LIMIT on DELETE degrade performance dramatically?

I have a database project in php and mysql. For, hopefully redundant, data security I added a LIMIT 1 to the delete($uniqueID) php function we use. Nobody cared because records really aren't ...
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31 views

EXPLAIN (with subqueries) is giving results I don't understand

I have a query that relies on a subquery, and that subquery relies on another subquery. When I run an EXPLAIN on the full query, in does a full table scan of the table in the primary select. However, ...
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54 views

Is it best practice to include partition keys within foreign keys when referencing partitioned tables?

The large tables in our database are partitioned by an id in order to separate data and speed up IO. The table of the data is partitioned by the partition key, but the primary key is only on an ...
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179 views

Oracle 11.2 Explain Plan takes too long

I'm using Oracle 11.2 SE on a 16GB Xeon E3 Linux machine as well as 11.2 XE on a 8GB i7 Win8 machine: SELECT banner FROM v$version: Oracle Database 11g Release 11.2.0.4.0 - 64bit Production PL/SQL ...
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1answer
97 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 ...
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61 views

Last few rows from a non-indexed table in Oracle

I'm trying to run a query on an Oracle DB through SQL Server [dont' ask, it's a requirement] The Oracle table in question [lets call it hugeTable] has over 200 million rows and no index. I'm not ...
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63 views

Mysql query with LIMIT much slower under RDS (5.6) than old 5.1 system

We inherited an old legacy system running on mysql 5.1, and moved it to RDS running 5.6. One query is running much slower - it can take up to 20 minutes to run, where previously it took only a few ...
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18 views

Documents with many potentially overlapping geolocations (maybe MongoDB)

Let's say I have a large list of coordinates coupled with the type of building is at this location (e.g., restaurant, doctor's office). In this scenario, there would potentially be many different ...
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65 views

Index Tuning Question

I have the following query: SELECT T1.ITEMID, T1.ITEMTYPE, T1.PURCHMODEL, T1.HEIGHT, T1.WIDTH, T1.SALESMODEL, T1.COSTGROUPID, T1.REQGROUPID, T1.EPCMANAGER, ...
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0answers
42 views

How to optimize having bit_or?

Let's start with SQLFiddle http://www.sqlfiddle.com/#!2/64fc5/1 I have some urls and I am making some tasks (crons) related to them. Task can be successful or not. I want to try to do it only three ...
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0answers
33 views

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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67 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 ...
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2answers
242 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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0answers
65 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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1answer
86 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` ( ...
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47 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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0answers
77 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 ...
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38 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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0answers
51 views

Why is PostgreSQL doing a seq scan on column != column?

Why is PostgreSQL doing a table scan on column != column? Isn't this query guaranteed to return no results? Isn't anything != anything guaranteed to be always false for any record on a not null ...
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0answers
77 views

Slow query (Wordpress)

Can I speed up somehow the following query? Somehow to stop from creating a tmp table/filesort. Tried a couple of indexes but no luck. mysql> explain SELECT wp_posts.ID FROM wp_posts LEFT JOIN ...
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18 views

View in View slower to execute?

Sometimes it's easier and clearer arranged to create a View from another View. Can this cause some speed losses in relation to selecting everything just in one Big and long View-Command?
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1answer
32 views

selecting rows that have n foreign key conditions satisfied

I'm trying to filter a master table rows based on 2-more conditions from the relative foreign key relation, i came up with this which is working fine, but i just can't convince my self that it's that ...
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1answer
3k 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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0answers
98 views

INDEX SKIP SCAN performance on Index where first columns only contain 1 value

We're running an Oracle 11.2.0.3 database and have a table with above 10 columns in it. There is a non-unique index over all these columns. For simplicity in this example, lets assume the columns are ...
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0answers
25 views

Analize Query in MySQL Server 5.1

I try use MySQL Workbench 6 to analyze the cost, but they don't show the cost of query. How i get this costs?