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

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109 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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53 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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2answers
103 views

Simple query is slow on 4M-rows table

I have in production a MySQL table pageviews with 4M rows that records page views of users on posts. I need to know which posts a specific user have read, but this request takes up to 15 seconds to ...
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0answers
32 views

PLSQL using cursors or functions to query repeated data

Is it better to declare a commonly used lookup query as a package function or as a function (either returning rows or values or returning a sysref cursor)? Whats the difference? What are the best ...
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0answers
35 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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1answer
68 views

optimizing query for slow queries

I have this query in my slowqueries table which essentially is taking about 5-8 seconds to complete the query time: SELECT s0_.id AS id0, s0_.updated AS updated1, s0_.created AS created2, ...
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0answers
128 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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1answer
40 views

Mysql query performance

We have a database table and we found a weird query from old code. We can't really explain it, so we decided to analyze why it could have been done that way. The weird thing is that the results are ...
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0answers
62 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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41 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 ...
2
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1answer
108 views

MySQL: Why queries with subqueries are much faster than single query?

I made few queries on my db lately First query: SELECT `table`.* FROM (`table`) WHERE table.id in(27172172,[...bunch of ids...],27171770) ORDER BY field (`table`.`id`, ...
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1answer
42 views

Mathematical or Computing Alternatives for MySQL Combination Queries operating toward their Performance Limit

We regularly run a contest that is becoming quite popular. In the contest, we need to select the combinations of contestants from 8 groups whose cost is under a threshold, and who combined have the ...
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3answers
502 views

Speed of MySQL query for the most recent 800 entries in chronological order

I have a MySQL database running on an Ubuntu box that pings 250 clients once a minute (24x7). My column names are: ip_address varchar(16), status varchar(7), timestamp datetime Been running it for ...
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2answers
499 views

Filter table before join

I have a stored procedure that populates the temp table #employee_benefits with a list of Ids. This table ends up being roughly 10,000 rows long. The query below then selects from a table called ...
7
votes
1answer
212 views

Query optimizer recommends adding index instead of using existing index

I am trying to determine why the query optimizer in SQL Server is recommending creating a new index instead of using an existing index that appears to be sufficient for the query. First the table. ...
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0answers
43 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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4answers
101 views

Why does this query take 32 sec to execute?

I keep my history records in one table and my pertinent data in another. I want to grab only the files from myfiles that currently have a given status recorded in statuses (ie, the latest status is ...
1
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1answer
83 views

Query performance issues

I need help in improving the performance of the following query. It has the purpose to select one record out of a group of records with an identical ID (doublettes). Rules are that Date2 must be the ...
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0answers
14 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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2answers
92 views

Fourth inner join to the same table increases query duration significantly

As soon as I add a fourth inner join to a specific table, the query duration increases significantly: sub 1sec to 45sec. The table in question is deployments d4. The SQL Query: select a.id as ...
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3answers
62 views

Performance first low, then high after adding index, then keep high after drop index

I am testing performance a complicated select query. It is very slow. using explain, I have found a ALL in type COLUMN. Then I ADD INDEX. result comes out fast. However, when I DROP the INDEX I ...
1
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1answer
43 views

How to query a list of all the different errors?

I have a DB which is very big and stores a lot of eventlogs, around 15 million rows. When I try this query, it is totally impossible to get some results. Any idea how I could do this? Maybe indexed ...
3
votes
2answers
1k views

Dramatic decrease in SQL Azure performance after scaling to new edition

Yesterday, we scaled one of our databases in Azure from the old Business edition to the new Standard one (S2). Since then, it has been behaving rather erratically. We have a relatively simple table ...
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0answers
77 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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1answer
72 views

Summing a column based on uniqueness of another column without using temporary table

I have a table like this: CREATE TABLE `files` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, `hash` char(40) DEFAULT NULL, `size` bigint(20) unsigned DEFAULT '0', ...
1
vote
1answer
90 views

SQL : get rows from two tables relatively

I've two tables named categories and products. Simple structure is given below. categories cat_id cat_name 1 c1 2 c2 3 c3 products prod_id ...
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0answers
84 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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1answer
38 views

How can I speed up this simple query

I am trying to speed a query that grabs data to be used to display a graph for a research project. It's currently VERY slow. It has 18295603 items only and takes about 20s per query. Here is an ...
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2answers
163 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 ...
1
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1answer
141 views

Deciding which MySQL execution plan is better

Background: I have a query that I'm trying to speed up, involving 3 tables: omgenvelope has 5 million rows omgcust has 195 rows omginput has 35836 rows I'm obtaining the distinct omginputs ...
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0answers
40 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 ...
2
votes
1answer
1k views

Mysql search matching multiple values in multiple columns

I need to speed up a search. Currently we let our users input a name: John Doe Then in Java we split that string to create multiple values (or "terms") ["John", "Doe"] and loop through the terms ...
4
votes
3answers
1k views

Slow queries on billions-rows-table // index used

Since I'm a young developer and not really skilled in using databases (PostgreSQL 9.3) I ran into some problems with a project, where I really need help with. My project is about collecting data of ...
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0answers
68 views

Odd Execution Plan

I have a table in SQL Server that is performing very slowly and I have been trying different indexing options to try to speed it up to no avail. I suspect all of the varchar(max) fields may be a ...
0
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1answer
162 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
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1answer
112 views

Slow running aggregate of aggregate query

I am looking for the total balance for all accounts that had a negative balance as of a specific point in time. I've already got the code below, and it works, but works horribly. The transactions ...
1
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1answer
49 views

How much should I care about prepared statements for simple queries?

I wonder how much I should care about prepared statements (and therefore try to optimize my code) in case of pretty simple statements. The question originates from the fact that I recently noticed ...
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0answers
39 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 ...
1
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1answer
231 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 ...
2
votes
3answers
97 views

Change table scan in query plan to seek

I have an ORM generated query (Django) running against a local Postgres 9.1.11 instance that looks up ~5 records from two specific match fields. Due to the nature of the EDI load program, I need to ...
1
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1answer
1k views

MySQL SUM with multiple GROUP BY on same table

What is the best way to produce several sum results based on different group by conditions on the same table in MySQL? I believe I'm doing a bad select, but I can't figure out a better way. Imagine ...
1
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0answers
67 views

How to use join with this query? [closed]

This query is working fine, and giving the right result. In this query all columns are in one table, but now I have made some changes. Now columns named Semester and Major are in different Table ...
0
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2answers
362 views

Tsql Query speed slow due to Or within where clause, causing index scan instead of seek

I have been working on making this query work more efficiently. I found that the number of Ors within the where clause are the biggest problem within this query. This query sits in a stored ...
2
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0answers
47 views

Optimization suggestions for db2 materialized view

I have a view for db2 9.7 which has consolidated o/p from few tables. The view is built and it is working fine I want optimization suggestions on the view SQL CREATE VIEW XYZZ AS SELECT ...
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0answers
46 views

Copying to tmp table slow for query … but only sometimes

I have a query, and I admit it may not be the prettiest query in the world. Sometimes this query runs fairly fast (e.g. 200ms) and other times it runs super slow (e.g. 30s). I don't know why, and ...
0
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0answers
17 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 ...
0
votes
1answer
110 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 ...
0
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2answers
80 views

Querying MySQL, duration increases 10x fold after adding one more Join

I have a somewhat complicated query consisting of many joins on an issue tracker/project management database in MySQL. My issue is that my query was doing OK while I was in the process of building it ...
2
votes
1answer
76 views

Running a query on an improperly indexed, 600gb table

This is my first post on here and I'm really baffled by this. I have joined a team and somewhere in the past a horrific table was created which has been bloated to a point of 600+gb of data. ...
1
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1answer
52 views

pt-query-digest results are empty

I have a slow log generated by MySQL 5.1.71-log, that I've copied onto another machine. It appears I'm not getting any results from pt-query-digest. $> pt-query-digest slow.log # 2.1s user time, ...