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

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81 views

Speed efficient query for membership first joined, latest category from membership table (min, max)

I have the following table representing membership information: CREATE TABLE IF NOT EXISTS `membership` ( `id` int(11) NOT NULL AUTO_INCREMENT, `organisation_id` int(11) NOT NULL, ...
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1answer
383 views

slow queries - set weight to token type in tsquery - postgresql

Postgresql version 9.2.3! I'm working on a database for mapping of chemical names. My main table contains aprox 91 million records and it's indexed by gin. I want to query it with multiple names (I'm ...
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1answer
64 views

Faster joining on 'most recent' related rows

I have a bug tracking application. The bug table stores very little, because every state change to a bug happens by adding a comment. For example, the current state of a bug is determined by the state ...
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1answer
113 views

Query taking long time

My query is taking around 540 seconds to get result. Please help me to rewrite it. Query: SELECT pd.domain, fd.passkeyid FROM portfolio.domains AS pd, fabulousdomains.domains AS fd WHERE ...
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1answer
127 views

Reviewing all new MySql queries on staging environment

The problem I am trying to solve: It's well known that not all developers know what is EXPLAIN in MySql, and not every knows how to use it. Large part of them consider MySql as a black box, no matter ...
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1answer
275 views

MySQL Partition based on month-year

Is there a way that I can create a month-year partition on the below table? Without having to define all the permuations of month/year combos ? CREATE TABLE visitor_visits ( id int(10) UNSIGNED ...
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1answer
2k views

Is there an easy way to debug and find out why a query runs slow?

I'm running onto a weird issue. We've got two db servers, one is development and the other one is production. Both have same specs. VMs (Hyper-V) Windows Server 2008 R2 64 Bit SQL Server 2008 R2 64 ...
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2answers
222 views

Attempting to avoid SORT in query planner

I have a query that is used VERY frequently in my application. Without modifying the query itself, I'm trying to optimize it by toying with different indexing schemes. Here's the query (basically): ...
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134 views

Help me to better design my query so I can gain more performance

I need to find so called first entry in database for items regarding their partners. I wrote query and it is giving me correct results but it sucks with performances. I suspect that I have missed ...
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1answer
350 views

Returning Multiple Result-Sets or Single XML Blods

I've been writing some new Stored Procedures, and find myself returning between 6-8 result-sets in a few cases. I've always worked under the assumption that there were certain inefficiencies with ...
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1answer
43 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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21 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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1answer
22 views

How to optimize a very slow query with joins and group by?

I have this GTFS database : All the ***_id columns are indexed, and there are foreign keys between tables (such as a FK on trips.route_id to routes.route_id). So basically the link between a stop ...
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0answers
61 views

High Logical Reads for Worktable [closed]

I have a very complex logic SQL Query which has many case statement. It is running very slow. It has 7 Left Join tables. Updated Execution Plan Link Below Statistics of sample query. what could ...
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0answers
9 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
61 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
33 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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26 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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13 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
70 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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0answers
25 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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1answer
69 views

How to increase sql server performance? denormalization (making cascade delete off) vs making duplicate data

I have a database with following related table ( sql server enterptise edtion 2014) each state have many citites which each city has may municpalArea and so on State => Cities = > ...
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41 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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80 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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33 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
10 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
48 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 ...
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1answer
20 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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20 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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27 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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71 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
48 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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54 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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30 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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14 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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55 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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39 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
12 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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3answers
109 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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50 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
125 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
59 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
63 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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0answers
31 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
46 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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28 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
44 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
42 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
28 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 ...