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

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74 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 ...
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630 views

How to improve query performance in PostgreSQL? [closed]

I have the following query to be execute within a second but getting time for execute 2.8 minutes: Query: Using Common Table Expression. explain analyze with temp_cte as ( Select ...
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25 views

Optimize finding the next batch of data from A to be crunched and inserted into B

I'm using PostgreSQL to store data produced by a large distributed computation. There are several stages to this computation; the idiom we've settled on is that there's a table containing the results ...
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1answer
1k views

SQL hourly data aggregation in postgresql

I am a newbie with database so I'm seeking your help with this one. I have a table containing time series data. 2012/01/01 00:10, 10 2012/01/01 00:30, 5 2012/01/01 01:00, 10 2012/01/01 01:40, 10 ...
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65 views

Why is one of these queries orders of magnitude slower than the other?

Sorry for the vague headline question. Essentially, and I know this is generally terrible practice, but I have query with nested subqueries as follows: SELECT * FROM ibt1 WHERE basetype = 60 ...
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23 views

Difference in the workload related to data-amount and search option

A couple of days ago I was asked why it is necessary to use the first normal form also for separation of names. We have a table which stores private customers (Name+Surname;Information) and business ...
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54 views

Microsoft Access database performance

I wonder how MS Access manage to show long list of records when we want to browse theme in Datasheet view. 1 - Does it load limited amount of records on start-up and then load the remainder upon user ...
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158 views

Best database for fast read all in one table [closed]

I currently have a large database in SQLite that I was using for rapid-prototyping for a software I am working on. Now that I am planning to move it to another database that should give better ...
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103 views

MySQL query with order by decreased performance

Here is my schema: CREATE TABLE `UserMst` ( `UserID` mediumint(8) unsigned NOT NULL AUTO_INCREMENT, `EMailID` varchar(50) DEFAULT NULL, `UserName` varchar(20) DEFAULT NULL, `FullName` ...
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189 views

MySQL aggregation count performance

I have a table with about 30 million records, and I'm doing a query where I can group by field Year and count the results for that year. The table structure looks like: id | year | amount The ...
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1answer
4k views

Query State hangs on sending data

For some reason, the query state hangs on "Sending Data" (using show processlist;) and I have no idea why. This is the table creating script: CREATE TABLE IF NOT EXISTS `esp_game` ( `gameID` ...
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128 views

join performance, index vs. index+foreignkey

I'm using an orm framework that handles data (and its integrity) on top of mysql. So far I ignored foreign keys because the orm handles that just fine. I recently read that foreign keys can enhance ...
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4answers
322 views

Which of these queries is best for performance?

Which of these queries are best for performance ? Sometimes I wonder if SHORT scripts really is the best thing to focus on. These scripts performs the same task. With left joins i can achieve what i ...
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95 views

MySQL: What criteria should I base my table column order/arrangement/grouping on?

Does the order, arrangement or grouping of columns with large (such as long text descriptions) and small (such as bit and tinyint) field types have any noticeable impact on MySQL (InnoDB engine) ...
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0answers
53 views

Optimizing a query using derived tables [duplicate]

As part of a daily cron job, I need to run a query that processes a whole lot of data. This data is related to the visitors coming to a website, and updating the data with what we have captured ...
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0answers
311 views

Sql Execution Plan - Hash Match

I'm currently working on a Sql Query that's having performance issues. I ran the execution plan and saw the Hash Match has 50% cost and also, doing a index scan. I'm starting to learning about the ...
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4k views

How to speed up query on table with millions of rows

The Issue: I'm working on a big table that consists about 37mln rows. Data include measurements of many devices made in certain time e.g. '2013-09-24 10:45:50'. Each day all of those devices are ...
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3answers
4k views

Simple select is taking too long

I am facing an issue with the performance. The selection of data from table is taking more than 20 sec to retrieve close to 300k records. Created a clustered index on col1 and col2 but no improvement. ...
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1answer
481 views

Retrieving data speed tweaks SQL Server 2005

I have a database in Microsoft SQL Server 2005. I have table with 3 columns, namely HASHKEY (BIGINT), NOTE_ID (INT) and TIME_OFFSET (INT). Columns HASHKEY has 19 digit BIGINT values, which can ...
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267 views

Read vs. Write speed

In the data import procedures I have, I get external raw data and import it into tables. I don't just overwrite the data, even if it is only from one source, but before I allow an update, I check if ...
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154 views

Mysql performance issue when selecting text column

I have a performance problem when selecting rows containing text fields: SELECT id FROM message WHERE NOT(message.sender_id = 368352 AND message.is_deleted_sender = 1) AND ...
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0answers
163 views

Optimising Large SQL Server Tables [closed]

I have a large table with around 50 million rows and 15 columns. Whenever I read, I always need all columns so I can't split them. I have a clustered index on the table with 4 keys (ALL INT) and I ...
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175 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 ...
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132 views

Identical Postgres index scan taking 5x longer on server [closed]

I have an intermediate table for managing a many-to-many relation between tables called Expert and Subject: Column | Type | Modifiers ...
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3answers
4k 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 ...
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1answer
183 views

SQL Server 2008 search joining query

I have two table as one is the message table and another one is messageUser table. Now i need to check before insert a new row. for example, M_MessageMessageId========= ...
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485 views

SOLVED: Postgres 8.4.5: Bad query plan vs Good query plan when changing date range on large data table

SOLVED. I was able to resolve this issue by altering the time.date column to allow 1000 stats: ALTER TABLE time ALTER COLUMN date SET STATISTICS 1000; Now the queries are running very fast, down to ...
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212 views

How can I use mongoDB efficiently in this scenario?

I'm trying to build a system of documents that have hundreds of tags assigned to them, but each document-tag association has a certain condition it has to also meet so the document would be returned: ...
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1answer
293 views

mysql freeze/crash on JOIN

here is query: SELECT nw.news_id, nw.title, nw.description, nw.url, nw.date, nw.image, nw.status, src.title as src_title, src.keyword as src_keyword, src.url as src_url, src.icon as ...
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1answer
483 views

Optimizing User Defined Custom Columns

I am building a web based app that has the potential to have very high traffic and collect a lot of data. Most of this traffic will be utilizing the database. Database is MySQL InnoDB. I want to give ...
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2answers
1k views

Slow mysql fulltext query

I have a little problem with the performance of a mysql-query which uses a fulltext index. The following query SELECT Mention.id FROM mentions AS Mention WHERE (MATCH (`Mention`.`title_text`, ...
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2answers
200 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
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1answer
425 views

MySQL query optimization with aggregate ORDER BY

I have an analytics table that stores metrics aggregated the day level. I need to ask questions such as "For a given date range and client, what are the most popular items." The schema is as follows: ...
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1answer
138 views

Slow queries InnoDB occasionaly

I have the next table: CREATE TABLE `sessions` ( `session_id` char(32) COLLATE utf8_unicode_ci NOT NULL, `session_expires` int(11) NOT NULL DEFAULT '0', `session_data` varchar(10000) COLLATE ...
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2answers
60 views

How to improve perfomance or Query Execution Time in MySQL?

This is my query: SELECT a.z_companyid_pk "z_companyid_pk" , a.company_name "Client" , a.display_name "Display_Name" , ...
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4answers
655 views

Can migration from MS Access to SQL Server or … make database faster? [closed]

A company asked me to migrate their database from MS Access to SQL Server or MySQL because they think that on those engines their database will run faster. But I wonder if their problem isn't because ...
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2answers
97 views

Can I improve this query?

SELECT * FROM SameLogTable WHERE ID_Table IN (SELECT ID_Table-1 FROM SameLogTable WHERE <SameCondition>) OR ID_Table IN (SELECT ID_Table ...
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1answer
60 views

execution plan question

I have this query running for long time (@P0 nvarchar(4000)) select emaildmo0_.Id as Id7_ ,emaildmo0_.CreatedDate as CreatedD2_7_ ,emaildmo0_.EmailAddress as EmailAdd3_7_ ...
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2answers
91 views

How can I replace the following query with ISNULL function in SQL?

I have the following query. For performance optimization reasons I have been asked to replace the logic with ISNULL function in SQL. How can I achieve this? please advice. SELECT ...
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4answers
143 views

Single SQL query to retrieve data in a particular order (not ASC/DESC)

I have a MySQL table, let's say called reviews review_id, product_id, language_id, rating, review, author language_id ranges from 1 to 10 for 10 different languages. Let's say I determine that my ...
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2answers
474 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 ...
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2answers
242 views

Database SQL Script very, very slow (string manipulation over 700k rows)

I have table containing 700,000 rows containing a string id field with values such as rec-232276-dup-0 and rec-354240-org. The rec- is constant but the other parts of the id can change. I want to ...
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2answers
876 views

Why would a long running query remain sleeping and with null wait_info

The following query was run on SQL Server 2008 R2 and took over 1 hour to run: select log_id, type, instance_id from ts_cache_log where log_id > 146400 order by log_id It produced 0 rows ...
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3answers
5k views

Will more indexes on a table affect performance? [duplicate]

Possible Duplicate: How do indices impact query performance? How to know when/if I have too many indexes? Say ‘X’ report using some "where" condition in the statement so we are creating ...
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2answers
69 views

Oracle query optimization

We have a query that runs on a view and its execution time is about 6 min. SELECT COUNT(*) FROM someschema.item_total_violations WHERE channel_id = 122507833 AND item_date >= ...
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1answer
68 views

Similar hardware, Same DBconfiguration and Database but different status variables result between Windows and Linux server [closed]

I have two database servers - one is Windows - 2008 and another is RHEL5 with similar hardware configuration. Both OS are 64 bit. MySQL 5.1.58 community edition is installed on Windows servers while ...
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2answers
60 views

Which one is better way to insert data? [closed]

I have two cases case create proc createEmployee @firstName varchar(255), @lastName varchar(255) = null as insert into Employee_Tbl values (@firstName, @lastName) case create proc ...
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2answers
72 views

A simple database and Query System? [closed]

I am new to databases and trying to solve one problem in which I have to build a simple database having few entries and then querying that database and then recording that answers from the database. I ...
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2answers
1k views

How to get rid of using temporary when using DISTINCT in MySQL?

When I do the following, I get Using where; Using index; Using temporary. How do I get rid of Using temporary? http://sqlfiddle.com/#!8/f61a2/3/0 CREATE TABLE `test` ( `a` varchar(45) NOT NULL, ...
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3answers
2k views

Duration Field in Profiler

I would like to monitor the script which takes more than 25 Sec. When i use filter i am not able to see the duration taken by the script. How can we get the time taken to execute the query. My ...