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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How to index for a group by with columns from different tables?

Is it possible to create an index from columns of 2 different tables? If not, how do we optimize a query that does a group by on columns of 2 different tables? For example: the following ...
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199 views

Optimising Large SQL Server Tables [closed]

I have a large table with around 50 million rows and 15 columns. Whenever I read, I always need all columns so I can't split them. I have a clustered index on the table with 4 keys (ALL INT) and I ...
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221 views

Mysql key_buffer_size already 16GB but some fulltext searches are still slow

I have a query w/ full text search which takes 5 - 10 secs. key_buffer_size is already 16GB. Table has 15 million records and has a compound fulltext index on fields: categories and company. Table ...
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1answer
2k views

MySQL dynamically optimize innodb tables without “file per table” setting

We are getting a “too many connections” error once a week the same time a mysql procedure runs. The procedure runs “optimize table” on hundreds of tables and takes nearly ten hours to finish, taking ...
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How can I join one to one to (many to one) without using group_concat

I have a table structure as follows: -- -- Table structure for table `emails` -- CREATE TABLE IF NOT EXISTS `emails` ( `ID` int(5) NOT NULL AUTO_INCREMENT, `email` varchar(255) COLLATE ...
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4answers
203 views

Normalization of DB

I have designed a database using MySQL likewise My question is what else i can do to normalize the DB, for now i am using InnoDB engine for the table to maintain the relation among different tables. ...
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528 views

Finding the bottleneck by analyzing Munin graphs

We’ve been experiencing some issues with our database server during peak hours. In our Nginx error-log we can see that a lot of requests get timed out. The requests are also very slow. We have had ...
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1answer
966 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? ...
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2answers
2k views

Slow mysql fulltext query

I have a little problem with the performance of a mysql-query which uses a fulltext index. The following query SELECT Mention.id FROM mentions AS Mention WHERE (MATCH (`Mention`.`title_text`, ...
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2answers
106 views

Basic PARTITION question in MySQL

Say I have an application using MySQL and at some point decide that implementing Partitions on certain tables might improve performance. Would I need to change the applications select statements ...
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0answers
59 views

Link-table(s) vs Redundant Columns? [duplicate]

Possible Duplicate: Would it be considered as a bad practice to have multiple nullable FKs on a table in SQL Server I have two tables, Users and People, both of which share a common ...
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1answer
632 views

Optimization: Delete with Top and minimize the where clause date range

I have a delete statement that get run repetitive until all the data are removed. Delete TOP (1000) From Log Where CreationDate < '2011-Dec-31' AND pKey NOT IN (...) I am considering of ...
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1answer
277 views

Why is my stored procedure very much slower than the same MYSQL query? [duplicate]

My stored procedure is very slow compared to a normal query or a temporary table. How can I optimize my stored procedure? CREATE DEFINER=`datasll`@`...` PROCEDURE `product`() BEGIN EXPLAIN ...
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2answers
97 views

How to improve perfomance or Query Execution Time in MySQL?

This is my query: SELECT a.z_companyid_pk "z_companyid_pk" , a.company_name "Client" , a.display_name "Display_Name" , ...
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2answers
207 views

Long running simple query SQL Server 2008 R2 [closed]

I have a very simple query running in a SQL Server 2008 R2 instance: SELECT TOP 10 * FROM messages m INNER JOIN recipients r ON m.id = r.id WHERE m.timeStamp > '2014-07-14T00:00:00.000' AND ...
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2answers
42 views

What are the SET options that affect Plan Reuse and how to get their values in T-SQL?

I'm troubleshooting the case when a stored procedure runs great from the management studio at any time, but the same stored procedure can run terribly badly in one of the webservers, even for the same ...
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2answers
144 views

Force Sql server to use index seek in merge join

I am testing Merge join in sql server. I have an INNER JOIN and force the optimizer to do MERGE JOIN: ID in Personal Table is a Primary key ID in Abteilung Table is a primary key There is no other ...
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2answers
71 views

How to use max function in such condition?

My query is select * from guestuser union select * from olduser ORDER BY userid DESC LIMIT 1; Is that correct query to find last userid from different table have different userid? can i change ...
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2answers
101 views

How can I make this query more efficient?

This is the query: SELECT races.*, tmptimers.last_start_time, tmplaps.updated_at AS last_updated_at FROM races LEFT JOIN (SELECT * FROM timers WHERE timers.user_id = 1) AS tmptimers ON ...
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1answer
455 views

Why query optimizer doesn't use negative filter index

I have a table that has following structure, as you can see, there are one clustered index and two non-clustered indexes, one non-clustered index is IX_ParentId_Include, and another one is ...
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1answer
100 views

What's the biggest bottleneck (time) in writing data to a SQL database?

I'm running an ETL process that is writing about 2 million rows to a SQL Server database. I'm trying to optimize the time it takes for pure inserts (I guess updates is a different story). I'm ...
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2answers
56 views

why the optimizer doesn't choose the optimal plan [closed]

I know, if the statistic is not updatad, it is possible, that the optimizer doesn't choose the optimal execution plan? Does any other reason/reasons exist?
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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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1answer
109 views

On which fields to index? Fields queried (WHERE) or fields returned (SELECT)

I have a large MySQL database table (~1 million rows and growing) on an AWS RDS Medium instance: mysql> describe clients; ...
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2answers
3k views

Is there a good reason to store big text data outside database?

I was analyzing my MySQL database performance and found that tables containing text fields are just huge, larger than 1Gb. This data is only used when loading single record (like article or blog ...
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1answer
66 views

NC Index not being used [closed]

I have a table (9mm records) with a field called filename nvarchar(max)(I didn't decide on this datatype and can't change it). I'm wanting to count how many records meet the following criteria: ...
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1answer
470 views

sql-server optimize query with lots of null checks

I have a query such as: select something from somewhere join stuff on condition join more_stuff on condition where somewhere.sometime is null and somewhere.someone is null and stuff.whatever is null ...
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3answers
197 views

Optimize extremely slow SQL query [closed]

SELECT j.job_id,j.last_updated,j.job_title,j.status, (SELECT COUNT(*) FROM candidates WHERE job_id=j.job_id) resumes_count, (SELECT COUNT(*) FROM candidates c WHERE job_id=j.job_id AND c.ref_type=1) ...
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2answers
2k views

How can I truly DELETE data from a SQL Server table - still shows up in notepad in backup file?

SQL Server DELETE only marks as DELETED though leaves as data in the data pages. Data pages are 1024 KB in size and this problem can be eliminated by adding a FILLFACTOR that ensures only 1 record ...
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1answer
62 views

get all the count of sub category from the product table in single query with mysql optimization [closed]

Table structure: CREATE TABLE some_table ( `product_id` int(11) NOT NULL AUTO_INCREMENT, `product_name` varchar(255) NOT NULL, `Product_model` varchar(255) NOT NULL, `product_discount` ...
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2answers
101 views

PostgreSQL How to optimize a query with ORDER BY and LIMIT 1?

I have the following PostgreSQL schema: CREATE TABLE User ( ID INTEGER PRIMARY KEY ); CREATE TABLE BOX ( ID INTEGER PRIMARY KEY ); CREATE SEQUENCE seq_item; CREATE TABLE Item ( ID ...
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2answers
1k views

How can I speed up this query on table with 65 million records

select hash_id, hash_value, substring(T.cri, 1, 7), substring(T.cri, 9, D2.Pos-9), substring(T.cri, D2.Pos + 1, D3.Pos - D2.Pos - 1), ...
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1answer
508 views

Where does mysql write temporary tables?

MySQL 5.1.x | Windows Server 2008 Data Directory is on a different partition. I have an innodb database (innodb_file_per_table is set) that I'm trying to optimize and I don't appear to have enough ...
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2answers
4k views

How can I better optimize my tables and a LEFT JOIN query to find items that don't yet exist in the right table?

I have two tables that represent a list of urls and their related word indexes. Here are the table definitions for reference. desc urllist; ...
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2answers
2k views

Use timestamp(or datetime) as part of primary key (or part of clustered index)

I use following query frequently: SELECT * FROM table WHERE Timestamp > [SomeTime] AND Timestamp < [SomeOtherTime] and publish = 1 and type = 2 order by Timestamp I would like to optimize ...
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1answer
2k views

Optimizing ORDER BY for simple MySQL query

I'm trying to optimize this really simple query, and it gives me grief for a day now :( Seems pretty straightforward, I need to select with a JOIN from 2 tables, and get top X results sorted in a ...
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1answer
389 views

Database schema design help needed

I am developing a PHP application expecting millions of records both parent and children. My goal is to design an optimized database design to achieve high speed and performance. This application ...
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1answer
7k views

Mysql 5.5: Optimizing all tables with mysqlcheck - is it useful to run the -check option along with -optimize?

I plan on running 'mysqlcheck --optimize --all-databases' to clear up some fragmentation. Would it be useful to run -check with this option or does the -optimize already take care of that? I am only ...
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1answer
635 views

Why do aggregate functions alter the way my rows are fetched?

Running this query SELECT s0.id, s0.symbol, YEARWEEK(p0.datetime) AS label, p0.id AS point_id, p0.datetime, KG_FIRST(p0.open, p0.datetime) AS open, MAX(p0.high) AS high, ...
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2answers
22 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 ...
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1answer
31 views

Php, MySql - Optimisation

I asked this on the general site, but they suggested I come here for ultimate optimisation. It really boils down to which is faster; doing a load of calculations in php with database stuff that is ...
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1answer
30 views

Query not using indexes

I have a query which is not using the timestamp index and scanning 200 million records. I know that the query will not use the index if there is a function applied on top of it. However is there any ...
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1answer
110 views

Huge database… queries too slow. How to improve performance? [closed]

I'm currently managing a MySQL database with 30 million rows(many more to come). The entire database is 280GB. The server has 4GB of RAM and 3.2Ghz 4 core processor. The largest column stores an array ...
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2answers
118 views

SQL Server Estimated I/O Cost in real units

As I understand from other StackExchange posts, SQL Servers estimates are unitless meaning an Estimated I/O cost of 2.82387 doesn't refer to the time taken or disk I/O's, but a relative measure of how ...
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2answers
31 views

mySQL efficiency with inner join queries

I have two tables, both with about 1,000,000 rows. Here is the question I am trying to get mySQL to solve: return all record_ids from table_a where that id matches the cat_id in table_b, but only ...
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1answer
117 views

Optimizing queries vs. adding indexes

I have this very old and SLOW query that I am trying to optimize, but I am not sure I can do anything to it, but add more indexes on columns involved in WHERE, JOIN and ORDER BY. Query: SELECT TOP ...
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1answer
111 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? ...
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2answers
129 views

Multiple WHERE IN on multiple columns

I am not very experienced with sql queries and looking for an efficient way to perform the same WHERE IN condition on multiple columns. More specifically, i'm doing the following: SELECT a, b FROM ...
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3answers
120 views

Adding order by to a query is slowing down the query even after Indexing

While joining columns with huge data even after indexing the column order by is slowing down the query. Without order by query is executing within 2 secs. But with order by query is taking 145 secs. ...
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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 ...