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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Looking to improve query performance

This is my query: select S-Num.Title, jobs.JobNum, jobs.JobPart, Part.PartNum, jobs.RevisionNum, jobs.Seq, jobs.Parent, Part.PartDescription, ...
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1answer
138 views

Blocked sessions waiting with PAGELATCH_* wait types?

Edited : Why are sessions reporting being blocked but waiting with PAGELATCH_*, and not LCK_M_ related wait types? I previously assumed that SQL server would only report blocking sessions in the ...
2
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1answer
27 views

what monitor before applying changes on the server? - looking for a basic answer - starting point only

these settings were decision of our development team: there are 2 settings: 1 - max degree of parallelism 2 - optimize for ad hoc workloads On OUR_DEV_SERVER: 1. Run the following script: ...
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1answer
52 views

storing as smallint, querying as int

A multi-billion-row fact table in our database has 10 measures stored as int columns. The value ranges for some of these columns won't ever be above the +/-32K range of a smallint. To save I/O, we're ...
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1answer
34 views

How do I compare all tables with nonzero rowcounts (in an archive db) with tables of the same name in the line of business db?

(Full Disclosure: I am a software tester who is out of my depth. Because I am unable to get a definitive answer from the developer due to the necessary independence of the test team, I have to figure ...
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2answers
83 views

How can I defragment tables in MySQL?

I have a database named COUNTY. COUNTY has a fragmented table GEO. I executed OPTIMIZE TABLE GEO against the GEO table, but this returned the error "Table does not support optimize, doing ...
2
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1answer
37 views

Excluding rows by lots of ids

I need to exclude some rows that the user has already seen. Currently I am doing this by simply comparing the ids that the user has seen to the row's ids by running this query (there are also other ...
1
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1answer
844 views

MySQL UPDATE query stuck on “Sending Data” State

I am having difficulty getting an UPDATE query to successfully execute, due to the process getting stuck on "Sending Data" state. I feel this differs from similar questions about the "Sending Data" ...
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0answers
32 views

Query performance tuning with joins on views with large data

I've this query in oracle. This is basically the query of a BA report which I'm trying to tune. SELECT DIM_PROJECT_OL.PROGRAM_ID, DIM_ANALYTIC_STRUCT_ACCOUNT_OL.STRUCTURE_ID, ...
0
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1answer
54 views

Is there any better way in oracle to enable parallel other than this?

I want to do do following set of operation. execute immediate "alter session enable parallel query"; execute immediate "alter session enable parallel ddl"; execute immediate "alter session set ...
12
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2answers
302 views

Why do SQL Server row estimates change when I add a join hint?

I have a query that joins a few tables and performs pretty badly - row estimates are way (a 1000 times) off and Nested Loops join is chosen, resulting in multiple table scans. The shape of the query ...
1
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1answer
1k views

Mysql Optimization suggessions

I have an InnoDB database table with more than 2 million rows. I am running efficienty indexed queries to reduce server load, but site becomes slower day by day. I ran Mysqltuner.pl to identify any ...
2
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1answer
722 views

Help required with query (join) optimization

I am working with a fact table source query and I have observed that performance of the query is pathetic. It has increased from 1:00 min to 6:30 min by just using a function in the select clause ...
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2answers
683 views

How to lower “Created_tmp_disk_tables” - temporary tables count created on DISK?

I have a ubuntu, mysql 5.6 DB that is heavy used by thousands of users. After 10 days of running I have this values: | Created_tmp_disk_tables | 894170 | | Created_tmp_files | 26068 | | ...
1
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3answers
97 views

Why does the query plan still sort a table despite having an index sorted on the columns?

I'm using Postgres 9.1 I have two tables I am joining: wikidb=> \d page Table "public.page" Column | Type | Modifiers ...
1
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2answers
136 views

Multiple-View Query Optimisation

We have a monster view that contains joins to many (many) tables in order to return the data that is required. In some cases, to get a column of information, we've have to join onto 4 tables, just to ...
2
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1answer
51 views

Tuning a query with: index, window function?

Description Environment: Centos 6-x64, Postgres Plus Advanced Server 9.3. I have a table with 4 columns with data as below: id code_id effective_date name 24 12 ...
11
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1answer
112 views

Why do these similar queries use different optimisation phases (transaction processing vs quick plan)?

The example code in this connect item Shows a bug where SELECT COUNT(*) FROM dbo.my_splitter_1('2') L1 INNER JOIN dbo.my_splitter_1('') L2 ON L1.csv_item = L2.csv_item Returns ...
2
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1answer
104 views

Understanding performance of highly unique WHERE clauses

I've been struggling to understand how to deal with a specific type of performance issue that shows up very often in this scenario: when you are wanting to apply multiple filters in a query, but you ...
2
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1answer
210 views

Two updates cause a deadlock

I have a mysql queue with the following sheme: CREATE TABLE IF NOT EXISTS `media` ( `mid` int(11) NOT NULL AUTO_INCREMENT, `order_type` int(11) NOT NULL, `media_id` varchar(50) COLLATE ...
2
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1answer
98 views

How to tune the query on all_constraints in Oracle 12c?

How to tune the following query, as it's taking around 8 seconds: select constraint_name,table_name from all_constraints where r_constraint_name in ...
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1answer
63 views

Query optimization in case of TIMESTAMPDIFF

I have a table where I need to delete all rows older than 5 hours. Currently I'm doing: delete from my_table where TIMESTAMPDIFF(HOUR, from_unixtime(round(created_on/1000)), now()) > 5 The ...
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1answer
298 views

Is there a way I can shorten the below query into a single query?

I have the below query. IS there a way I can put this into one single query? If not, can I shrink it further anyway? Please advice. DECLARE @highRegion TABLE(regionId INT, countR INT) DECLARE ...
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2answers
918 views

Will a WHERE query do checks on simpler comparisons (i.e. bit) before running more arduous comparisons (i.e. varchar)?

If I write a query that includes a compound WHERE clause, e.g.: SELECT * FROM MyTable WHERE BitField = 1 AND VarcharField = 'asdf' and the inclusion of that bit comparison simply excludes the ...
0
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3answers
187 views

Optimize mysql --> 'show global status'

I am working in the optimization of a MySQL Wordpress database running in a RDS instance at Amazon AWS. The instance is a t2.medium machine with 4GiB of RAM and 2vCPU. The size of the DB in a sql file ...
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1answer
33 views

Database: what design to have a “document table” referencing others tables

I have some tables which can have 0..* documents. How can I design my data model to avoid having a specific document table for each of my tables? Feel free to suggest by editing the data model
3
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0answers
196 views

Form builder schema for SQL database?

There are many ways one can envision the solution, from the top of my head: Two table approach: Field table with (name, field_name, type, description, meta) attributes Form table with (name, ...
2
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2answers
89 views

MariaDB server with 80K-100K DataBases

BACKGROUND : We have an environment where there is a new DB created almost every minute and it will be Dropped after few days or weeks (maximum 1 month) such that the space used is about 300GB~400GB ...
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2answers
183 views

Optimization of variables in my.cnf (mysql) for Drupal

I just get a Dedicated Server running UBUNTU and I need to optimize the variables in my.cnf for Drupal 7. I understand that this is tailed job. Then Is there any tool to help me to do this? I am a ...
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0answers
102 views

How come MySQL LIKE is faster then FULLTEXT?

So, I was trying to optimize my MySQL queries, but found out that i'm actually doing this wrong. I've changed my query from using SELECT * FROM test WHERE tst_title LIKE '1%' To: SELECT * FROM ...
1
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3answers
68 views

Is it safe to run optimze on mutliple tables in parallel in mysql (percona)

I have a slave on which no query is coming. Lot of data has been archived and deleted from almost all tables. Size of tables vary from 80Gb to few Mbs. And there are around 130 such tables. Mysql ...
3
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1answer
103 views

4m Rows in MySQL, ~5 Minutes to Run Query

I have 2 tables, a users table and a log table which literally logs each time a user signs in. What I'm trying to do is grab a list of all users with a certain rank who have not logged in for over a ...
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2answers
74 views

How to optimise MySQL query that uses dependent subquery

I have a web app that has a custom feed of images. The image queried are based on whether the users have previously seen the image and ordered by a Hacker News style score. There are only 1000 rows ...
0
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1answer
40 views

Is it advisable to asynchronously update the summary table every time a transaction is deleted?

Given three tables: (a) Product (b) Transaction Head (c) Transaction Detail We need to create a query that fetches a list of products with associated latest ordered quantity and latest transaction ...
2
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2answers
54 views

Optimizing query using a WHILE statement

I'm trying to convert a view that extracts a yearly amount into something more WHILEish The query is more or less: SELECT * FROM (SELECT SUM(EmployeePaid)*2 AS Total2013 FROM TblRecords WHERE FYear ...
2
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1answer
85 views

How to merge partitions in Postgres?

I have a table that is partitioned by date on a monthly basis beginning January 1, 2014. There is significantly more rows of data in 2015 than there were in 2014 and the data in 2014 is not accessed ...
5
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1answer
108 views

Joining in query decomposition

I have a question about query decomposition and localization, as in here: When joining 3 tables (here EMP, ASG and PROJ) is there any specifiy order, when to join which table? Why ASG and EMP are ...
3
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2answers
94 views

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 ...
2
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2answers
132 views

MySQL: memory requirements for django app with 1 big table (460M rows)

I have created a django app that is running on virtual machine. All db tables are rather small (up to 1M rows) but recently I was asked to add a big table (460M rows). CREATE TABLE `genescorrelation` ...
5
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2answers
96 views

Will I need to create a pivot or can I alter this query

The following Query that I wrote is working to a point. The problem that I found is that in each pump, cable, etc can be listed in each of the part columns. Example: What I would like to get is ...
0
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1answer
107 views

Oracle 11g PGA advice view is empty when it shouldn't

I have the following situation in an Oracle 11g server (it's part of a RAC). PGA_AGGREGATE_TARGET is set, STATISTICS_LEVEL is TYPICAL, and yet V$PGA_TARGET_ADVICE shows up empty. Why does this happen? ...
7
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1answer
194 views

Which is more efficient b+ tree or search (binary or linear)?

SELECT A FROM T WHERE M > 1000 AND M < 5000; I am unable to judge which of the below is best suited for the above query: Linear search Binary search on M B+-tree with index on M B+-tree with ...
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2answers
80 views

Optimize query or split in two queries and process result separately?

I have this DB schema: As you may notice already there is no relationship between tables and won't be on the future. If I run the following queries I will get a lot of rows per table: SELECT ...
2
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2answers
371 views

Why the WHERE clause is not pushed down in the view's query?

With Postgres 9.4, I'm doing the following query quite often: SELECT DISTINCT ON(recipient) * FROM messages LEFT JOIN identities ON messages.recipient = identities.name WHERE timestamp BETWEEN timeA ...
2
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1answer
155 views

How can I optimize searching a column for a sub-string in SQL Server?

I have a very basic table: CREATE TABLE [obj_local] ( [obj_id] INT NOT NULL, [value] NVARCHAR (1000) NOT NULL ); This table stores a lot of data, and I need to search ...
4
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2answers
2k 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 ...
12
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3answers
316 views

Predicates: in the WHERE clause or the JOIN clause? [duplicate]

Looking at "SQL Server 2008 Internals"1 by Kalen Delaney, on page 13, it states the following: "The first step in producing such a plan is to normalize each query, which potentially breaks down a ...
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0answers
118 views

Performance Issue on Centos Server (Mysql)

I have performance issue on my centos server (vps). I asked about it in serverfault and I was said there is a problem with mysql and ask here. Here is serverfault topic, you can find details. ...
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1answer
69 views

Is smallest to largest the rule of thumb in a multi-table JOIN?

Given this query, SELECT a.* FROM a LEFT JOIN b ON b.a_id = a.id LEFT JOIN c ON c.a_id = a.id HAVING COUNT(DISTINCT b.id) < COUNT(DISTINCT c.id) if b is a significantly larger table than c, will ...
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1answer
365 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, ...