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 optimize a log process in MySQL?

In my project, I have about 100.000 users and can't control their behavior. Now, what I would like to do is log their activity in a certain task. Every activity, is one record which includes columns ...
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2answers
4k views

How to setup mysql on tmpfs?

How to setup mysql on tmpfs ? I am reading a tutorial in french, where the author do it this way : 1.) Create a tmpfs directory : mkdir /var/tmpfs mount -t tmpfs -o size=1G tmpfs /var/tmpfs chown -...
3
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1answer
273 views

How does the MySQL Query Optimizer react to a SELECT COUNT sentence?

Let's say we have a table called "customers" with these columns ("id", "name", "country", "created_at). There's an index by ("country", "created_at"). If SELECT COUNT(*) FROM customers WHERE ID &...
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3answers
2k views

How to restructure this slow query containing subquery?

This query takes about 2-6 seconds to run depending which tag id(s) is/are selected: SELECT t2.id, t2.name, count(*) as kpl FROM (SELECT pt1.post_id FROM posts_tags pt1 WHERE pt1.tag_id ...
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3answers
68 views

IN Clause - listing values VS query

My app runs a lot of queries like this SELECT ... FROM Table WHERE CategoryID IN (SELECT CategoryID FROM OtherTable WHERE ..) To save performance I decided to cache the second subquery in the ...
3
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1answer
102 views

Optimizer gets the wrong number of estimated rows even with updated stats [closed]

I have a procedure running in SQL Server 2008 that contains a query similar to the one below; SELECT /* various columns from table 1 and table 2 */ FROM dbo.tbl_1 AS a INNER JOIN dbo.tbl_2 AS b ON a....
3
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1answer
125 views

Improve performance of query with multiple group by column and count function in select

Brief Background of issue We have a aggregate table to store activities of competitors and this table have currently 3 Million activities and we need to retrieve data from this table group by ...
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1answer
45 views

Postgres reduce by key if key is not null

I need to select N rows with seq > X which reduce_key is null and for each row group with the same reduce_key select the one with the biggest seq. Result should be strictly sequential (but with ...
3
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2answers
71 views

Should I normalise this database?

I have two database designs thought of for storing messages(instant messages) between users. It will be a group chat system. I have two table designs in mind. One is this: CREATE TABLE `...
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1answer
1k views

Mongodb high lock percentage / slow queries

I'm working with an application using MongoDB that is getting a fairly large number of incoming requests and I've noticed that the responses are getting slower as the number of requests get higher. ...
3
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1answer
245 views

When is mariadb creating tmp tables?

I have found, that copying to tmp table is taking most of the time of a slow query, that I wanted to optimize. I watched the output of 'profiling' in a terminal. This happens on a pics table with 6000 ...
3
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2answers
154 views

How to optimize this slow SQL query

I have a slow SQL query on my Drupal website and I don't know how to optimize it. Here is the query that Views produces: http://pastebin.com/StAEiXbY SQL fiddle: http://sqlfiddle.com/#!2/20081/1/0 ...
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2answers
93 views

Designating databases to certain CPUs

SQL Server 2012. AlwaysOn Cluster with two nodes, each has 4 cores We are consolidating SQL server instances and moving bunch of databases from various locations to a single cluster which has two ...
3
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1answer
225 views

Mysql Fragmentation. How bad is too bad?

I ran a table status for my companies production site and its showing close to around '49085939712' for just about every table in my database and we have around 400 tables. I am not a DB ...
3
votes
1answer
105 views

PostgreSQL + query planner + amount of entities

I'm working on a college assignment about how the query planner uses statistics and makes the most optimal query plan. I have read the 57.1. Row Estimation Examples article and I know how PostgreSQL ...
3
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1answer
54 views

Timestamp Difference - Syntax Error - Condtitional Selects

Here is what I have right now SELECT name, admin, reason, unban, FROM_UNIXTIME(date) AS datetime, HOUR(difference) AS HRemain, MINUTE(difference) AS MRemain FROM (SEC_TO_TIME(AVG(TIMESTAMPDIFF(MINUTE,...
3
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3answers
405 views

Having both a integer Primary Key and a GUID/UUID collumn on same table-is this bad

I have my MySQL database having tables where on each table, we have a ID (int,auto increment) Clustered Primary key and a UUID(varchar36) collumn thats just a GUID. The ID is there just for indexing ...
3
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1answer
116 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 ...
3
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1answer
106 views

MySQL query WHERE IN + ORDER BY, which EXPLAIN is better and how to avoid filesort?

This is my table definition, without any special index for now: CREATE TABLE `filter` ( `field_name` varchar(32) COLLATE utf8_unicode_ci NOT NULL, `category_id` varchar(32) COLLATE ...
3
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1answer
106 views

Improve performance on SQL Server Query

I'm trying to increase the performance of a query and I'm out of ideas: The query does this: gets a 'Process' with specific priorities on selection namely: Picks up a process that has been waiting ...
3
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1answer
130 views

Simple SELECT takes forever, but works as a subquery. Why?

I'm running a MySQL 5.1 server and I have a MyISAM table called my_table with nearly 5 million records. Its structure is the following: +---------------------------------------------------------------...
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1answer
356 views

Problem with PostgreSQL and the geqo optimizer

I'm trying to compare the two execution plans (exhaustive search and geqo) from the optimizer, but I always get the same plan from both types. These are the variables I use for geqo: SET geqo = true; ...
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1answer
582 views

mysql: need help to optimize my query/table

I'm wondering if someone could help me optimize my tables/query to speed up a query. It is currently running ridiculously slow. I think a well-thought out index could help me. Any help would be really ...
3
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1answer
949 views

Mysql Server optimization tips needed! (InnoDB)

I've recently been trying to optimize our mysql server but I've encountered some pretty serious problems on the way. We're running a game server which is coded in C#. We have two dedicated servers. ...
3
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1answer
3k views

Optimizing MySQL for Read-Only?

We have 14 GB worth of CSV's which total 138 million rows. I imported this into a MySQL table first with InnoDB, and then tried again with MyISAM. In both cases, a simple SELECT on primary key (...
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1answer
118 views

How can I find out which statistics are evaluated by the optimizer?

My enterprise has a farm of many nearly-identical, isolated production environments. Each environment has a SQL Server 2005 database server, each supporting a database with nearly identical schemas. ...
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1answer
139 views

How to search for an ID and its descendants in this query?

I have the following tables: Project Unit ------------- --------------- ID | IDUnit ID | IdParent I have to select all projects that have the IDUnit ...
3
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1answer
713 views

MySQL query 'going away' on executing INSERT ON DUPLICATE UPDATE statement with a 12524 character blob

I have a mysql insert on update query like so insert into table (col1, col2, col3) values (1,2,'huge blob with 12524 chars') on duplicate key update col3 = 'huge blob with 12524 chars'; col1, col2 ...
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0answers
89 views

Heavy I/O for Microsoft Transaction Log

We have a Microsoft SQL Server (SQL Server 2012 SP3), we've noticed that transaction log I/O is very high. We do have a busy server; we're hosted at Rackspace with SSD block storage. The Logs are are ...
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0answers
157 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. ...
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0answers
60 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 ...
3
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1answer
46 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 ...
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67 views

Optimizing an Intersect query between two huge spatial tables

I am having a hard time trying to improve an intersect between two spatial tables and I would like to receive any tips about the table designs, queries or dba configs. Tables: Table "teste....
3
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1answer
190 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 '...
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0answers
226 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, ...
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0answers
102 views

Why the stored procedure is much slower than a temporary table? [closed]

I want to do the updating of my database every day and I will like to use stored procedures but the time of execution of the temporary table is faster than the stored procedure. How can I optimize my ...
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418 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 ...
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0answers
70 views

Tagged questions

I have similar to StackExchange network that utilises tagged questions. In my web application Users also can find questions by tags. The query below returns a set of tagged questions: SELECT ...
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0answers
427 views

How to count selectivity rows in PostgreSQL 8.2

I have problem with two queries on PostgreSQL v8.2. It seem like the optimizer chooses a wrong index: db=# explain select count(*), messagetype, alias from event where templateinfoid = 10 and ...
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894 views

MySQL: Improve performance for one row insert into table with unique constraint

I have a table with ~ 40 mil records, with a unique index on the url collumn, of type varchar(255). Now the insert speed is about 30/s, is this expected? how could I improve it? I can't use bulk ...
3
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1answer
2k views

Mysql - show results from 3 tables excluding NULL or EMPTY values for certain fields

I have 3 simple tables with polls, users and votes. I'd like to show all polls ordered by clean count of votes (sometimes either poll_id or user_id don't get inserted). Furthermore I'd like to show ...
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0answers
1k views

Best book on query optimization, rewriting, refactoring [closed]

I have a specific problem: huge amounts of Web-related data in Postgres db. The queries running against the data are often very inefficient. But in a more general sense, I need a book that explains ...
2
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2answers
430 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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2answers
265 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 ...
2
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1answer
744 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 ...
2
votes
1answer
6k views

Why isn't oracle using an index for distinct query ?

This is the scenario SQL> exec dbms_stats.gather_table_stats(user,'TM', cascade=>true) PL/SQL procedure successfully completed. SQL> SELECT SEGMENT_NAME , SEGMENT_TYPE , BYTES / 1024 / ...
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2answers
324 views

Why does adding LIMIT to my query make it crawl?

Simple query: select sum(score) total,name,gender,dob,country from users join scores on users.id = scores.user_id where date between '2012-01-01' and '2012-01-31 23:59:59' group by scores.user_id ...
2
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1answer
3k views

Will OPTIMIZE TABLE have any impact on my data?

I'm having issues with a database that is getting quite slow. The analyzer in phpMyAdmin recommends that I run OPTIMIZE TABLE on my tables. But before doing so, I would (of course) like to know if ...