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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+100

Increase in IO Wait after adding indexes with postgres

I've recently been put in charge of a system that has been fairly untended for a period of time. The majority of activity is via queued worker jobs based off of data feeds from other systems/data ...
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0answers
5 views

MySQL: excessive memory usage

In our production system, MySQL service uses above 95 % of the available memory. System Info: OS: CentOS 6 RAM: 32 GB CPU: 4 core MySQL version: MySQL 5.5 Database Size: 158 GB my.cnf info: # ...
3
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0answers
101 views

Best procedure to measure query optimization effects?

I could not find valuable answers or explanations to the following question: How should a procedure to test query improvements effects look like? Using SSMS I am not absolutely sure about the steps. ...
0
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0answers
34 views

Statistics shows CPU time = 0 ms, elapsed time = 0 on second time and query running blazing fast?

I tried to run this query on a database which is located on my network, but not on my own computer. set statistics time on SELECT id, status FROM MyTable EXEC MySproc @id='3000021' set statistics ...
2
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1answer
183 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 ...
2
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0answers
99 views

Advice on how to improve this stored procedure

Edited: Added table column datatype I have 2 tables ReportItem id (int, primary key clustered index) report_item (nvarchar(100)) flow_name (nvarchar(50)) source (nvarchar(50)) Tech_Details id ...
1
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1answer
603 views

Optimising a query of an SSRS dataset

Consider the query given below: SELECT * FROM ((SELECT c.cust_id , c.username , REPLACE(qs.seg_type_ref_key_02, 'N/A', 'Non Vip') casino_group, ...
0
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1answer
113 views

Better ways than rownum limits on a union all for fallback-style queries?

I have three queries that generates some "reference" statistics and should be tried in order until one returns a result. These are currently coded as three separate calls to the DB, but I want to ...
3
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0answers
40 views

Slow Postgresql query with left join

I have a query on Postgres, and I also have added proper index. Is there anything missing here? SELECT orders.*, demo.name as d_name FROM orders LEFT JOIN users as demo ON demo.id = orders.dr_id ...
0
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0answers
43 views

Goals for Future Database Systems [closed]

What are the features that you would like to see in future database systems ? What are some of the complicated tasks that you need to perform in current database systems that could be simplified by a ...
2
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2answers
172 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) ...
1
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0answers
27 views

PostgreSQL 9.3 Query Design Optimisation - Improving speed

I am looking to optimise a query that is currently taking ~2500ms to run in PostgreSQL 9.3. The reason I need to optimise it is that may have to be run frequently and it directly impacts user ...
0
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0answers
42 views

how to find overlapping or duplicated indexes? when is it O.K. to keep them?

this is a script that does the following: create a database called "radha" for testing purposes, create the table ProductItemDetailsDenorm create the clustered primary key create ...
2
votes
1answer
2k views

MySQL InnoDB page_cleaner settings might not be optimal

Seeing this note in mysqld.log: [Note] InnoDB: page_cleaner: 1000ms intended loop took 15888ms. The settings might not be optimal. (flushed=200 and evicted=0, during the time.) There seems to be ...
3
votes
2answers
45 views

Fill in missing dates with data value from previous populated date for group

Picture help desk tickets that gets transfered between departments. We want to know what the department is at the end of the day for each ticket for each day that the ticket is open. The table ...
0
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0answers
15 views

Optimal Number of Queries Per Batch for SQL Server

I am optimizing an application for a scenario where it will import an sql file and execute over 11 million create commands, which have have some expensive subqueries that are outside my control. This ...
0
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0answers
75 views

SQL query too slow to fetch single row of data

we have this SP, running extremely slow to fetch a single row of data from tables within 100K rows, which seems not that big. It takes onn avg 15-20 mins to complete. We have tried to remove all ...
3
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0answers
40 views

Online text based game design - Am I linking the databases correctly?

I'm trying to recreate an old game that I used to play that went offline quite some time ago. I'm doing this as a hobby project for myself with the hope that maybe a few hundred people might enjoy it ...
1
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2answers
53 views

How to improve performance of a query with an IN subquery

Get the count of other users having the x tag with order_id in order_id of users having the y tag table: MyCustomTable (200K rows) order_id user_id type ('x' and 'y') my custom tags and the ...
2
votes
1answer
643 views

Oracle 11g bug ? not returning the record until I triggered index to invisible and then to visible

We are using Oracle 11g, 11.2.0.3. We know a record exists in a table but a select is not returning it for some odd reason. The execution plans the general query, not forcing any index, shows that ...
1
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0answers
23 views

optimize a window aggregate function

First, the query SELECT tc.numreg, com.numdep, tc.numcom, tc.numiris, sum(tc.conso_climat_reel)/sum(sum(tc.conso_climat_reel)) OVER (PARTITION BY tc.numreg) AS ratio, ...
1
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1answer
38 views

are overlapping multi column statistics redundant?

I have run a database engine tuning advisor session, DTA, to optimize my database. The DTA has produced some statistics recommendations, however, I noticed some are contained in others for example ...
3
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2answers
44 views

Poor SELECT performance on recheck cond with data and large (millions of rows) partial index

Query: EXPLAIN (ANALYZE, BUFFERS) SELECT COUNT (*) AS "count" FROM "Posts" AS "Post" WHERE "Post"."createdAt" > '2015-08-19 14:55:50.398' AND "Post"."new" = TRUE; Index: CREATE ...
4
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2answers
206 views

Optimize query to find top N users who commented on a post

Problem Trying to find the most efficient query to retrieve the top N (5 in the examples) users who have commented on a post, where a user is considered 'top' if they have the most followers. The ...
7
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3answers
247 views

Execution Plan is NOT using INDEX, It uses Table Scan

I know when it comes to using an index or a table scan, SQL Server uses statistics to see which one is better. I have a table with 20 million rows. I have an index on (SnapshotKey, Measure) and this ...
0
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1answer
28 views

How to list the missing multicolumn statistics?

I have used the database engine tuning advisor, DTA, in order to improve the performance of one of my databases. It produced a list of recommendations, mostly multicolumn statistics. These ...
0
votes
1answer
35 views

In what circumstances I am more likely to benefit from auto update stats async on?

I update statistics on a weekly basis using Ola Hallengren's solution. Based on the article below, I am considering enabling the Auto Stats Async and turning on trace flag 2371. Databases With ...
2
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2answers
251 views

Using the database engine tuning advisor - how do I generate the scripts for the recommendations?

I have run a server-side profile trace for over an hour to produce a .trc file with all activities in one of my databases. I have then passed this .trc trace file as a parameter to the database ...
5
votes
2answers
4k 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 ...
3
votes
2answers
193 views

IN Clause - performance difference between listing values and query

I changed this query SELECT ... FROM linkedServer.DB.Schema.Table1 t1 LEFT JOIN linkedServer.DB.Schema.Table2 t2 ON t1.ORDER_ID = t2.ORDER_ID WHERE t1.BRANCH_ID NOT IN ( '009991', '009992', ...
5
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0answers
92 views

SQL Server Sharding strategy optimization

I have implemented a sharding solution for our SQL Server databases as per the MSDN documentation here: https://msdn.microsoft.com/en-gb/library/dn589797.aspx This has been running for around 6 ...
1
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1answer
30 views

Subquery inside a select vs left join

Often I have to return the count of of some row in a query that fetch other non related rows. For example A table User a table Review and a Table picture User: id nickname Review: id to_user_id ...
3
votes
2answers
264 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
11
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2answers
150 views

Queries without Good Enough Plan Found

I have a SQL Server 2012 database. I noticed value of Reason for early termination of statement optimization for some queries and all gave Good Enough Plan Found. Now my questions are: What are all ...
2
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0answers
26 views

Materialized Views and Indexes

Is there any way to force PostgreSQL to use an index that I created on a materialized view table? I tried every combination possible of moving the column attributes around to make Postgres to use my ...
4
votes
1answer
36 views

Question about cost optimization formula for SELECT

I am a student in computer science and I have a question, which refers to cost optimization. I have to read the book (Fundamentals of Database Systems from Elmasry and Navathe) and try to present the ...
1
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2answers
35 views

Slow query / Indexes creation (PostgreSQL 9.2)

I have the following Query: explain analyze SELECT split_part(full_path, '/', 4)::INT AS account_id, split_part(full_path, '/', 6)::INT AS note_id, split_part(full_path, '/', 9)::TEXT ...
2
votes
1answer
59 views

Query with Indexes slower than without Indexes

I'm using MySQL 5.6 and my storage engine is InnoDB. I have a table with 1 million rows containing with the columns: ID (primary key) FirstName LastName foreign_key_id (foreign key, NOT NULL) ...
1
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1answer
25 views

index creation - Slow Query - PostgreSQL 9.2

I've got the following query: SELECT * FROM ( SELECT split_part(full_path, '/', 4)::INT AS account_id, split_part(full_path, '/', 6)::INT AS note_id, split_part(full_path, '/', 9)::TEXT ...
1
vote
1answer
831 views

MySQL: Optimize query with a range and distinct count

I have a query on a large table with millions of rows that looks like this: SELECT COUNT( DISTINCT clicks.tx_id ) AS unique_clicks_count , clicks.offer_id FROM clicks WHERE ...
1
vote
1answer
427 views

MySQL Query with good execution plan is very slow due to Sending data operation

I have the following query: SELECT a.borrowerId AS borrower_id, a.created, NULL AS initiator_team_id, NULL AS initiator_user_id, NULL AS old_team_id, NULL AS old_user_id, ...
1
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1answer
982 views

Slow insert with MySQL full-text index

I use a full-text index in a MySQL table, and each insert into this table takes about 3 seconds. It seems that MySQL rebuilds (a part) of the full text index after each insert/update. Is this right? ...
1
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0answers
793 views

SQL server 2008 querying very large large tables

I've recently started a new job, the table row counts are huge compared to where I was before (11 billion rows in one of our main tables). I've been told there isn't time to update the statistics on ...
1
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0answers
34 views

Could auto_analyze cause inconsistent (and bad) query plans?

I have a simple table which stores metadata about users in an hstore column. This table has ~1.1M rows. Table "public.stitcher_participant" Column | Type ...
2
votes
1answer
706 views

How to improve the performance of SELECT queries with multiple JOINs on a 50GB database hosted on AWS m3.medium MySQL RDS?

Example query: SELECT p.ListAgentEmail, p.ListAgentFirstName, p.ListAgentLastName, p.ListingKey FROM Property_RES AS p INNER JOIN Property_RES_COUNTIES_OR_REGIONS ON ...
1
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2answers
81 views

How can I remove 'Using temporary ' and speed up my query

Hi I was working for hours to speed up this query using indexes, but its useless.. im tyring to optimize by eliminating 'Using temporary' and using only indexes. I wonder if there is another ...
1
vote
2answers
452 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 ...
27
votes
3answers
31k views

Optimizing queries on a range of timestamps (two columns)

I use PostgreSQL 9.1 on Ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one integer property. There are additional columns in my ...
1
vote
1answer
82 views

Why using where in indexed field is slow?

we have a big table. the table structure is : CREATE TABLE `visit_logs` ( `id` int(10) NOT NULL AUTO_INCREMENT, `user_id` int(10) NOT NULL, `ref_id` int(10) NOT NULL DEFAULT '0', `link_id` ...
3
votes
1answer
154 views

How to run OPTIMIZE TABLE on a 3-node cluster?

I've my hands on a 3-node Percona XtraDB Cluster where, according to mysqlcheck, some tables are corrupted (some indexes contain the wrong number of entries): mydb.mytable Warning : InnoDB: Index ...