In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

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Scheduled optimization of tables in MySQL InnoDB

What is the best way to schedule automatic optimization of tables in a MySQL InnoDB database? Can I use events for example? I have recently had a big performance issue (when querying) with one of the ...
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1answer
672 views

Speeding SQL queries for a large(?) WordPress database?

I am using a WordPress plugin called feedwordpress in order to run a planet like website (it takes content from other websites, with their permission) on WordPress (See it here). The plugin is great ...
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808 views

Fetch first 9 records and make one more record which will be as “Others” in MySQL

I am fetching records from one table with count of one field with other field as name. I want only 10 records. out of which 9 records give me field and its count. but i want to show 10 record as ...
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Optimizing queries on a range of timestamps (one column)

I am using Postgres 9.3 through Heroku. I have a table, "traffic", with 1M+ records that has many inserts and updates every day. I need to perform SUM operations across this table over different time ...
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157 views

Why is the CTE much worse than inline subqueries

Im trying to better understand how the query planner work in postgresql. I have this query: select id from users where id <> 2 and gender = (select gender from users where id = 2) ...
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834 views

TokuDB optimize table does not reclaim disk space

Was running an optimize table command against one of my tables about 11Gig in size, surprisingly used disk space grew by 2Gig immediately after optimization process finished. I would expect the ...
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1answer
1k views

ORDER BY optimization for a large table

I am currently aggregating posts from different social networks. Currently I have 50-100 million posts from Facebook, Twitter, Youtube, Instagram , Pinterest. Consider a table posts posts { id ...
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1answer
1k views

Simple MySQL query randomly takes forever

I'm having an issue on my server with a simple PHP send emails script that runs every minute via a cronjob. The script contains a MySQL query that runs very fast most of the time, but randomly will ...
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2answers
944 views

Website is too slow when number of records increases?

I have developed a web application called Referral Program, It it developed by using PHP, MySQL. Users can joining the website and when they introduce new members, he/she gets a commission. The system ...
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319 views

Optimal hash technique to index large text

Erwin Brandstetter thankfully saved me from myself when I tried to create unique indexes on textual columns with large lengths. The upper limit for the insertion rate is tens of billions of rows per ...
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1answer
185 views

sql indexing and performance

I am using mysql5.1, i have table which has about 15 lakh (1.5 million) records.This table has records for different entities i.e child records for all master entities. There are 8 columns in this ...
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1answer
3k views

Indexing strategy when using the between operator SQL Server 2008

I have a large table ~25 million rows with the structure CREATE TABLE [dbo].[rx]( [pat_id] [int] NOT NULL, [fill_Date] [date] NOT NULL, [script_End_Date] AS ...
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1answer
751 views

MongoDB optimization on high data

I have a mongoDB collection with 42M registers with 1M new registers every day. We found a low performance on mongoDB querying. showing in mongostat the fields: qr|qw ar|aw with values of 300-500. ...
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1answer
3k views

PostgreSQL tree structure and recursive CTE optimization

I'm trying to represent a tree structure in PostgreSQL (8.4) to be able to query the path from the root to a given node or to find all the nodes within a sub-branch. Here is a test table: CREATE ...
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1answer
776 views

Measuring the relative performance of queries given the assertion that “cost” isn't reliable

The cost field is a comparative cost that is used internally to determine the best cost for particular plans. The costs of different statements are not really directly comparable. Source Does ...
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2answers
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SQL Server Wildcardless LIKE Optimization

In a web application using SQL Server 2008 R2 as the backend, I have several fields, that if present, add WHERE clauses to the query. If I was to have all queries generated as like clauses, such as: ...
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1answer
127 views

How to partition existing table in postgres?

I would like to partition a table with 1M+ rows by date range. How is this commonly done without requiring much downtime or risking losing data? Here are the strategies I am considering, but open to ...
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1answer
223 views

How to determine cost/benefit of adding an index?

According to Craig Ringer: While it's usually a good idea to create an index on (or including) your referencing-side foreign key columns, it isn't required. Each index you add slows DML operations ...
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126 views

Logical optimization of joins and selections

I am studying query optimization. I have read that it might be preferred to apply relational selections before a logical join operation. Is there a scenario where joining first and then applying ...
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261 views

View with fallback (performance/optimization question)

I have a table with tariffs for stuff; the tariffs table is not important in this scenario, the "tariff values" are. In this Demonstration SQL Fiddle the tariff_plan is the FK to the tariffplans table ...
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1answer
116 views

How to get the information of the optimizer of sql server?

The info like total optimization time, the time spent on each stage of optimization, the number of alternative plans and the cost of each alternative plan. Is there any way to get these info using sql ...
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1answer
278 views

Optimizing MySQL -

I've been researching how to optimize MySQL a bit, but I still have a few questions. MySQL Primer Results http://pastie.org/private/lzjukl8wacxfjbjhge6vw Based on this, the first problem seems to be ...
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264 views

MySQL: A better way to write this query?

We are using the following query in our system: SELECT f.type AS type, COUNT(i.id) AS submissions, SUM((CASE (e.oiPost + e.oiPhone + e.oiEmail) WHEN 0 THEN 0 WHEN ...
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How to use the METHOD_OPT parameter in DBMS_STATS.gather_table_stats

Hi there I was just wondering what would be the difference between these 2 METHOD_OPT parameter settings: FOR COLUMNS SIZE 5 some_column and FOR COLUMNS some_column SIZE 5 both will create a ...
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1answer
222 views

SQL query filled Temdb complete Harddisk [closed]

I have a query which was earlier fine but now it is running me out of hard disk space with message that tempdb is full. My Harddisk has 90 gb of space as soon as i run query temdb runs out of space in ...
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Workaround for Anti-Semi Join bug

I built the following SQL Server query, but it is encountering the anti-semi join defect in SQL Server 2005 which results in inaccurate cardinality estimates (1 -- urgh!) and runs forever. Since it is ...
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Should we add extra 5 columns or build a separate table?

Currently we have a table with 35 fields in it. Now, we got a requirement to add 5 extra columns but these columns will not be fill always. So, I was thinking just add one column and have that id as ...
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SQL server tools to identify query optimisations and missing indexes [closed]

I have a broad question regarding SQL Server that was given to me on a quiz and I am not sure what the answer is as I do not have access to SQL Server at home. My question is how can I utilise SQL ...
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DBMS_REDEFINITION vs EXCHANGE PARTITION in oracle

In order to partition an existing non-partitioned table it is possible to use either the EXCHANGE PARTITION or DBMS_REDEFINITION. How to decide on which of those possibilities to choose for table ...
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How does TOPN influence a query with group by?

I have a query that looks like the following: Select t1.field1, t2.field2, sum(t1.field3) From t1 inner join t2 on t1.id = t2.id Group by t1.field1, t2.field2 It's simplified, normally there are a ...
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SQL Server Baseline and Performance Optimization

I've been struggling a little bit around Performance Troubleshooting including baseline and troubleshooting of SQL Performance. Could anyone help with this or point me to where I can possibly get a ...
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2answers
985 views

Upper or Lower Case Optimisation on MS SQL Server

Does anyone know if MS SQL Server text queries are optimised for upper or lower case strings? I read somewhere the it was uppercase, but cant seem to find the reference to it again. Of course if ...
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1answer
120 views

Does combining columns into 1 column helps to optimize a large table?

I have user, items and user_items tables, and as usual user has many items. Tables contains: User: ~50K Items: ~3.5M UserItems: ~5M I am using MySQL and most of my queries are selecting items of a ...
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forcing Oracle to use hash join for a subquery

I have a query that looks like SELECT * FROM table0 WHERE id IN (SELECT id FROM table1 JOIN table2) Oracle is choosing to join table0 with the result of (table1 x table2) using nested loops and ...
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Optimizing a query which runs through all hours in a day

I need help optimizing a query. I'm using PostgreSQL 9.3.4 currently but can upgrade to 9.4 if needed. I have a table with 60+ millions of records which looks like this: ...
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721 views

What are the options of reducing tempdb latency?

Took the job of monitoring and tununing a SQL Servers 2012 Enterprise Ed. SP1 (64 bit) on Windows Server 2008 R2 Standard Ed. All of them are running inside virtual machines. One SQL Server per a ...
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Searching for pairs of date/time values in a single row

I have a legacy IBM DB2 database table that contains lots of records of phone calls. It has columns for ID, customer number, employee who took the call, etc. The date/time for each call is kept in a ...
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Improving slow queries. Slow query log attached

Below is the Slow Query Log when my .NET application was running. Please let me know how to improve the performance of the queries: TCP Port: 3306, Named Pipe: (null) Time Id Command ...
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272 views

Does an empty column value occupy same storage space as a filled column value?

I have a table with 2 columns. The type of both columns is set to varchar(38). If I create a row with an empty value for one of the columns, will it take same storage space as if the value was not ...
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Mysql Index for concat select

For Below Query SELECT MAX(CONCAT(date, ' ', last_entry)) AS LAST_LOG FROM entry_log WHERE TRIM(LEADING 0 FROM card_no)='2948' I've index on date card_no date,last_entry ...
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1answer
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Maximum possible memory usage: 16.2G (874% of installed RAM)

Why the MySQL is saying that can use about 16GB of RAM even if my server has only about 2GB? # ./mysqltuner.pl >> MySQLTuner 1.2.0 - Major Hayden <major@mhtx.net> >> Bug ...
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Optimisation Newbie: How much of a 'sin' is redundancy?

I've been developing for a while, but never really had to deal with DB/scaling issues before. That's suddenly changed and I've found myself in the deep end. I have 2 SQL tables, as such: VOTES ...
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How can I optimize performance on a MySQL ndbcluster?

So, this is what I have: A simple table classes__to_students: |class |student| --------------- Math Alice Math Bob Math Peter Math Anne Music Bob Music Chis Music ...
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Moving data from table with VARCHAR(50) fields to table with numeric fields increases table size

I want to understand why migrating data in a table with all VARCHAR(50) fields to a table with optimized smaller types caused the new table (containing 61,065,164 rows) to be 4.46 GB, which is larger ...
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1answer
399 views

Has postgresql a fast add column optimization?

When adding not-null columns with a default value - does Postgresql optimizes this operation? In case the table has n rows, a not-optimized alter-table-add-column would yield n writes of the default ...
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1answer
325 views

How un-clustered is a CLUSTER USING table in PostgreSQL

I have some tables which benefit greatly from CLUSTER ON/CLUSTER USING in Postgres SQL: # CLUSTER table USING index_name; # ANALYZE VERBOSE table; # CLUSTER VERBOSE; A maintenance task periodically ...
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Correct use of VOLATILE COST (and ROWS) indications in Postgresql stored procedure

While looking at several examples of pl/python and pl/pgsql, I have seen many - but not all - using volatile cost. ie: CREATE OR REPLACE FUNCTION my_function() RETURNS setof record AS $BODY$ -- ...
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Subqueries run very fast individually, but when joined are very slow

ypercube solved the problem. Subqueries were totally unnecessary, and the whole thing works with plain joins. It is still strange that MySQL's optimizer could not make use of my original query, ...
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MySQL optimization - year column grouping - using temporary table, filesort

I have a transactions table which is having 600,000 records, I need to list the count for the dashboard on financial year basis. The table used is MyISAM. I tried adding index for the transaction date ...
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1answer
140 views

Analysing A Query Plan

Why is the following query slow? select count(*) from [dbo].[mt_dispatch_link] , [dbo].[_mt_dispatch] [_mt_dispatch] where (mt_dispatch_link.contract_id_1 = _mt_dispatch.contract_id ...