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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MySQL 2 Million Rows, longtext and varchar indexes

I'm trying to find a solution for this, with no success. I have a table with ~2M rows, and I need to do a WHERE with 3 expressions using OR. name LIKE '%PARAM%' OR text1 LIKE '%PARAM%' OR text2 LIKE ...
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87 views

Rolling update to all rows in innodb table (no rollback if aborted)

I have the following table, which stores the Social Security Death Master File database (~86M rows): CREATE TABLE `death_master_files` ( `id` int(11) NOT NULL AUTO_INCREMENT, `ssn_an` smallint(5) ...
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26 views

Optimizing MySQL for write throughput ceiling

We have a large MySQL database on AWS RDS, with a huge table around ~1.8TB with massive write workload. We recently hit a write throughput bottleneck, which caps our provisioned IOPS way below the ...
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39 views

Reducing query cache for mostly INSERT-heavy database?

What sort of MySQL query cache should I choose considering the following... Large, rapidly growing database (I got 500,000 rows). UPDATEs practically never happen. SELECTs are rare, but when they do ...
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176 views

Optimizing a CTE query - overhead in inserting into a new table from select statement

I have two tables with the same structure like so (let us call them initial_table1 and initial_table2): tempid name num_records 1 a 2 2 b 2 3 c 2 4 d ...
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3answers
334 views

MySQL - How do I Calculate an Average Value Over a Period of Time When Only Value Changes are Recorded

I am tracking the sales price of various items, and I would like to calculate the average price of each item over a period of time. My simplified tables look like this: Items ------------------ |key ...
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2answers
72 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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347 views

Is it possible to simplify a query with multiple joins to the same table?

I have a rather large query which takes longer to run than I would like because of 17 LEFT JOINs on the same table. I've done some searching, but haven't found anything that is really similar to my ...
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717 views

How does SQL Server's optimizer estimate the number of rows in a joined table?

I am running this query in the AdventureWorks2012 database: SELECT s.SalesOrderID, d.CarrierTrackingNumber, d.ProductID, d.OrderQty FROM Sales.SalesOrderHeader s JOIN ...
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72 views

MYSQL any way to improve this query's performance?

MYSQL version 5.6.23 CENTOS 7 Hi, I have the following query that is coming from an application that I am hoping to make more efficient from the mysql side of things. I have an index built on ...
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Best way to run a formula (segment) a large number of users with custom attributes

Here is my question. I have a table that stores a large number of people (80 mil). Each person has a GUID id. Then I have another table (or set of tables) that stores information about people. e.g. ...
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183 views

Get the latest record and count them with time interval

I have a table as below id fk_sales_id status created_at 1 001 5 2015-02-17 16:45:44 2 001 8 2015-02-18 18:45:44 3 002 30 2015-02-20 16:45:44 ...
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Subquery optimization

I was reading through this article - http://explainextended.com/2009/09/18/not-in-vs-not-exists-vs-left-join-is-null-mysql/ I am working with an existing design. What I want is to be able to select ...
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1answer
27 views

Optimize Query in MySQL

I've following tables with respective fields 1) wi_individual_g(ind_id,ind_is_recepient,ind_deleted,ind_district_id,...) - Around 200K data 2) wi_individual_p(ind_id,prg_id,...) Around 250K data 3) ...
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166 views

Is it possible to get seek based parallel plan for distinct/group by?

An example from this question shows that SQL Server will choose a full index scan to solve a query like this: select distinct [typeName] from [types] Where [typeName] has a non-clustered, ...
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62 views

Is there a way to improve this query further?

I've got a query that over time I've been improving. Originally it simply selected * from the records table, and the data was formatted on the webapp side. But that was slow and I wanted to make ...
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2answers
266 views

How to handle too many inserts?

I have a database that is accessed from remote locations in the world with very long delays and poor transfer speeds. I currently transfer the data using a transaction since either all or no data ...
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0answers
42 views

Oracle query optimization time

Is there any way to get how long it takes the optimizer to optimize a query in Oracle?
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Performance differs on same query against two (almost) identical tables?

I'm running these two queries in SQL Server 2012: SELECT tpua.Field1, CAST(round(twg.Field2 * 2, 0) / 2 As Decimal(8,1)) As Field2, CAST((round((twg.Field3/10.0) * 2, 0) / 2) * 10 As int) As ...
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58 views

Is there any way to trace the optimizer's work in Oracle?

Just like the MEMO structure in SQL Server which is kind of a "paper trail" of steps the optimizer takes in optimizing the query, is there anything in Oracle through which I can see what are the ...
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1answer
59 views

Is there any way to trace optimizer's work in DB2?

Just like the MEMO structure in SQL Server which is kind of a "paper trail" of steps the optimizer takes in optimizing the query, is there anything in DB2 through which I can get the information like, ...
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80 views

Replace nested “select with count” with outer join? is this possible?

SELECT c.classid , c.classname , (select count(s.id) from students s where s.classid = c.classid and status = 'failed') as noOfFailed, (select count(s.id) from students s where ...
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SQL - Optimize table population with dynamic queries

I need to optimize the following pl/sql procedure. So, fundamentally my question is: There is a way you can do a bulk insert in a pl/sql that could be more efficient than loop through an associative ...
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87 views

No value to update but still an TABLE UPDATE Operator

I see this type of code a lot in my databases IF EXISTS(SELECT 1 FROM sample WHERE ID=@id) BEGIN UPDATE sample SET name='cat' WHERE id=@id; END So from my primary analysis it does 2 scan in ...
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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 ...
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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 ...
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146 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 ...
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152 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 ...
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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" ...
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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 ...
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50 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 = ...
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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 ...
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112 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 ...
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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
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1answer
710 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 ...
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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 ...
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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 ...
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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 ...
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2answers
87 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 ...
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1answer
53 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 ...
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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 ...
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379 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 ...
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2answers
404 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 ...
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153 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 ...
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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
270 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 ...
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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 ...
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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 ...
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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. ...