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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2
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1answer
190 views

Joining two inline functions, slows considerably when filtering on second function

I have two inline functions that run quickly enough alone. When I left join them like this: select * from Function1(-1) F1 left join Function2(-1) F2 on F1.key = F2.key ...I get my result set in ...
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2answers
45 views

Is this query supposed to be slow?

Select * from (select tmp.userid userid, tmp.username ,tmp.likescore+tmp.commentscore+tmp.sharescore+tmp.tagscore+tmp.userscore+tmp.lsharescore+tmp.friendscore as score from ( SELECT u.userid,...
0
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2answers
151 views

Joining 4 tables and selecting distinct values based on 3 timestamps

I have been trying to remove duplicates from my query results based on the time but I would need to consider 3 different times and i am not sure how to do that. As some of the testing happen multiple ...
0
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0answers
164 views

sql taking < 1 sec to run in sql developer, 37 on the application side

As the title says, we have a big discrepency between a sql query we're running from our java application (jdbc thin client) and the same query run in sql developer. I clear the cache of the query ...
0
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1answer
45 views

Index for a Postgres query with a sort and an equality

This query is very slow: EXPLAIN (ANALYZE, buffers) SELECT * FROM "Follows" AS "Follow" INNER JOIN "Users" AS "followee" ON "Follow"."followeeId" = "followee"."id" WHERE "Follow"."followerId" ...
1
vote
1answer
69 views

What is causing an INTERSECT to run forever when the individual SELECTs run quickly? [closed]

I have a script that applies the INTERSECT operator to 2 separate queries. Query1 executes instantly and returns ~1k rows. Query2 executes almost instantly and returns 200k rows However, when ...
0
votes
1answer
51 views

MySQL script writing slow

I'm using php and the exec() function to run 2 MySQL script files one after another The first file has approx 2k update statements (see below) in and is 114kb in size. UPDATE table1 SET is_active = ...
0
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0answers
55 views

How I optimize data dump in oracle 11g

I've an Oracle 11g Database, now the data is very huge, I've an approximately 858 Object in 1 schema and i have 20 Schema, and it's about approx 20 TB in size. I've tried using Navicat Premium v11 to ...
0
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1answer
115 views

Best query to exclude existing friends from query

I have a User table / id_user / username / .. friends table (pair AB and BA): / friend_of / friend_to and a friend_request table (used for pending friend requests) / id_req/ sent_from / sent_to ...
3
votes
2answers
1k views

How to speed up select distinct?

I have a simple select distinct on some time series data: SELECT DISTINCT user_id FROM events WHERE project_id = 6 AND time > '2015-01-11 8:00:00' AND time < '2015-02-10 8:00:00'; And it ...
2
votes
1answer
746 views

Optimise select distinct from large table

I have a table that contains 320,071,712 number of records, the report that I am currently working on can filter the records by date, after which the number of records come down to 145,878,852. The ...
0
votes
1answer
46 views

Optimizing a MySql query

Here's the query: set @_YEAR = 2014; set @_MONTH = 1; set @_PRODUCTS = '53'; set @_START = date(@_YEAR * 10000 + 1 * 100 + 1); set @_END = date_add(date(@_YEAR * 10000 + 1 * 100 + 1), interval 1 ...
1
vote
1answer
131 views

Multi table GROUP BY query optimisation

Currently I have a multi table/column GROUP BY query which is pretty slow. Below is the tables schema used by the query: report Table ...
2
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0answers
31 views

Query optimization - contact should be extracted at most once for a particular customer

I have created a database for a telemarketing company Scenario is, the telemarketing company is selling contacts to the customers. Customers log on to the website and search for the contacts for ...
2
votes
2answers
88 views

How can one optimize a query involving a sort and a LIKE?

Here is the query: EXPLAIN ANALYZE SELECT * FROM "Users" AS "User" WHERE "User"."name" LIKE 'garr%' AND "User"."id" NOT IN (2449214) AND "User"."hellbanned" IS NULL AND "User"."...
0
votes
1answer
54 views

What is different between fixed-size disk pages and disk-based?

As per my knowledge, i understand fixed page size as size of page which used for read and write data but i am not able to understand what does mean of disk based ? I read these words from this paper ...
3
votes
2answers
1k views

Optimizing a Postgres query with a large IN

This query gets a list of posts created by people you follow. You can follow an unlimited number of people, but most people follow < 1000 others. With this style of query, the obvious optimization ...
3
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0answers
401 views

Slow transactions, many locks

At high load conditions the server app stops responding to client because begin/commit statements are executing very slowly (some take 15 seconds). The queries are simple - insert, update two columns ...
2
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0answers
43 views

Filtered Index is not selected once an identical, non-filtered, index is made [duplicate]

I have a lot of historical data, but 98% of the time, my data entry team only looks up data from the last 5 days. So I added a filtered index to help those lookups be faster. My test query looks ...
1
vote
2answers
433 views

Are nonclustered indexes used when joining tables?

I know that joins of type Sort-Merge don't use nonclustered indexes, because they work by sorting both tables and then joining them. But I've read recommendations to noncluster index all FKs, I ...
1
vote
0answers
158 views

How to optimize inefficient query in PostGIS

I'm doing some queries on a PostGIS, and some of them take a really long time ( > 60 secs). My queries are like this, except querying different tables (like osm_placesbelow). This query takes about ...
3
votes
1answer
1k views

Find out beforehand how many records a query has

I develop reports in ExtJS resulting of queries in SQL Server 2012. I use Ext.Grid with paging, therefore I can use offset to limit the amount of records a query will return. But for this ExtJS ...
3
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2answers
274 views

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 ...
1
vote
1answer
26 views

How to optimize search restricted by boolean column?

I want to optimize a query1 of the form SELECT yid, xid FROM x WHERE is_principal; Here, is_principal is a non-null boolean column of x. If I run EXPLAIN QUERY PLAN on this query, the output I get ...
1
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1answer
44 views

How to get paged resultset from a table?

I am trying to get paged resultset from a table (Notes). So, I am passing the last offset id (@LastOffset) value along with the page size (@Count). My approach to achieving this is: Sort the table ...
0
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0answers
33 views

SQL Server 2012: query to see queries that are consuming more resources [duplicate]

I'm trying to find/build a query to show me those queries that are consuming more resources in SQL Server so that I can optimize them or at least have a statistical idea of what is really happening. ...
1
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1answer
153 views

Incorrect unit allocation size. error comes when Tuning the Database

Here I am Using the SQL IDERA tool for checking the Index and performance of the Database, then i found below error, can any one tell what is it talking about. Incorrect unit allocation size. ...
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0answers
48 views

Can an index be added to a PRIMARY with a null key?

I have a query that takes a long time to return, roughly 12-15 seconds, which I'd like to optimize. The query below is the result of running the original query with SHOW WARNINGS. If I run EXPLAIN ...
0
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0answers
32 views

How can I optimize a query with multiple left joins?

The working example that I have been provided with takes about 20 minutes to fully process. http://paste2.org/G8BZvNHe What are some basic strategies for making this more efficient? Edit: I've ...
0
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2answers
799 views

What indexes should one use to optimize a PostgreSQL query with a JOIN depth of 2?

Disclaimer: I am relatively new to PostgreSQL. I'm wondering how to optimize a query that does 2 INNER JOINs. My scenario is fairly simple: Select Posts with a photo (Posts.photo IS NOT NULL) and a ...
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0answers
29 views

Creating separate small table from big based on access frequency for “select” performance

I have table with several millions of rows which are selected a lot (many times in a second in average). It is indexed and everything is ok for now. But performance is always a question (sometimes ...
2
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2answers
191 views

Slow subquery in SELECT statement

Having tried many different methods, I can't get my query taking shorter than 40 seconds to run with a dataset of ~11000 rows. The table is a list of hotel bookings, containing (most relevant) Check-...
1
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2answers
317 views

mysql multiple column index Cardinality order

How does Multiple-Column Indexes work in MySQL? How is it stored internally? consider a table with Multiple-Column Indexes on two columns (X,Y). If X has High-cardinality than Y i.e., X is less ...
1
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2answers
471 views

Optimize large table design

First, I am a complete novice when it comes to databases, but have been given the task to speed up queries on a large set of data. (Hundreds of millions of records) The current implementation is a ...
6
votes
2answers
2k views

Can rebuilding indexes cause worse performance after the rebuild is finished?

We have a customer database that is heavily fragmented - practically every table with more than 1000 pages has >95% fragmentation. Fill factors are set to sensible values, but page space usage is ...
1
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2answers
66 views

Get the pais_id not associated to fabricante_distribuidor_id and producto_solicitud_id, the opposite from SELECT query

I have this query for get all the pais_id given a fabricante_distribuidor_id and producto_solicitud_id, the query works fine. SELECT DISTINCT nom.pais_id FROM negocio.fabricante_producto_solicitud ...
0
votes
1answer
49 views

optimizing a select query of 1.5 million entry

I have the following query: SELECT s0_.id, s0_.lowresimageurl FROM app_instagram_shop_picture s0_ FORCE INDEX ( idx_deleted_shopId ) LEFT JOIN app_instagram_shop s1_ ON s0_.shop_id = s1_.id AND ( s1_....
2
votes
1answer
65 views

MySQL column type to boost performance

I'll have a table where: userid (link to user's id in users table) foldername (a varchar, max. 260 char) entry (varchar, max. 1024) data (varchar, max. 20kb) Single user will have several ...
1
vote
1answer
176 views

optimize design for a table with 50 columns [closed]

I have a table with 50 column and one of my friend has told me to split the table in 4 different table to save 12 column in each table. He proposed a design to have Master table and refer the PK of ...
0
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0answers
101 views

Large text column slows down whole table

I have a mysql database table table1 with a dozen columns in it. One column is a mediumtext column with lots of data in it and all the other columns are small (ints, timestamps, etc.). The presence ...
2
votes
1answer
194 views

Threshold for sort spill and random cardinality estimates

I wanted to test tempdb spill warnings so I run the following script on SQL Server 2014: USE tempdb IF OBJECT_ID('tempdb..tblTest') IS NOT NULL DROP TABLE tblTest CREATE TABLE tblTest ( ...
0
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0answers
453 views

Database design for price comparison site - too complex?

I'm working on a regular price comparison site with two exceptions. I want to show price history and also allow users to subscribe to a product with a specific size and color. As a result, I've ended ...
1
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0answers
106 views

Delete Query throwing warning db2

I am trying to delete multiple records from view The view has Instead of Trigger defined .. The view has records consolidated from multiple tables. [db2inst1@testServer001 ~]$ db2 "delete from ...
1
vote
0answers
360 views

How to Insert records from remote database to local database using dblink in postgresql 9.3

I have a scenario like i have a two DB, one resides in remote server and other resides local. Now i have to fetch the records from remote DB when new records are inserted on tables (in remote DB) and ...
4
votes
1answer
510 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) ...
0
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0answers
40 views

Create Temporary Index for bulk operation and Delete after its completed

I am moving bulk data to archive tables. Some times query returns up to 4.5million records, which takes about 2:15 minutes for a table of 40 columns. I want too increase the performance for the ...
1
vote
1answer
105 views

What would be most elegant way to replicate data contents periodically into a MySQL table?

I need to parse contents from an API route and insert into a MySQL database. The aim of parsing contents is to replicate the data from the API to my database table. I need to check API response every ...
3
votes
1answer
775 views

EXPLAIN ANALYZE shows no details for queries inside a plpgsql function

I am using a PL/pgSQL function in PostgreSQL 9.3 with several complex queries inside: create function f1() returns integer as $$ declare event tablename%ROWTYPE; .... .... begin FOR event IN ...