A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.

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173 views

Get and count all blog posts and all users that fits a LIKE condition (two sepparated queries)

I've this tables: -- -- Table structure for table `default_cmvblog` -- CREATE TABLE IF NOT EXISTS `default_cmvblog` ( `id` int(11) NOT NULL AUTO_INCREMENT, `title` varchar(100) COLLATE ...
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1answer
3k views

PostgreSQL 9.1 - Query on VIEWS taking a lot of time

Using PostgreSQL 9.1, we are having problems while executing queries on a VIEW of PostgreSQL. Following is the situation: We have a partitioned Table "buz_scdr" over which we have built a VIEW ...
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1answer
149 views

Reviewing all new MySql queries on staging environment

The problem I am trying to solve: It's well known that not all developers know what is EXPLAIN in MySql, and not every knows how to use it. Large part of them consider MySql as a black box, no matter ...
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1answer
43 views

Get wall_post and profile data for several users

I'm trying to build a query for fetch wall_posts and profile fields for several user_id. First see the images at: http://www.dropmocks.com/mBjQ7P. The table with id_user_rq, id_user_ap is the table ...
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1answer
216 views

MySql - How can I improve this query?

I have the following table: http://pastebin.com/XH6FvhZ8 and the following query: SELECT * FROM (SELECT * FROM `job_logs` ORDER BY id DESC) AS job_logs_tmp WHERE (job_logs_tmp.user_id = ...
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1answer
499 views

Oracle Benchmarking (SQL_NO_CACHE …)

I want to benchmark some queries on an oracle System from a JDBC application. However, the database seems to cache at some point in time. However, this is not intended in this case. Is there ...
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2answers
131 views

Improving MySQL efficiency

I have a table now containing over 43 million records. To execute SELECT, I usually select records with the same field, say A. Will it be more efficient to divide the table into several tables by ...
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0answers
11 views

Optiming ACT_RU_JOB Query

We're using Activiti version 5.15.1 with timers in our workflow which sends reminders to users who are in the workflow. Problem is that we're creating jobs in ACT_RU_JOB table and even though there ...
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1answer
27 views

Procedure to read from crontab like table and populate another one periodically

Postgres 9.3 Debian 7 I'm working on a mobile game project (poker like) where an admin user can register a recurrent tournament. As it's recurrent, I modeled it crontab like as follows. ...
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1answer
54 views

Query or a New Column for Performance

I have below tables: ProductsTable (has product details), UsersTable (has all application users), RatingCategry (category for which user can rate a products like Quality, Cost etc.) and ...
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2answers
62 views

Should I stop an awfully inefficient MySQL DELETE statement?

I'm running the following statement on MySQL 5.5 in a 1GB 1CPU SSD virtual machine from Linode: DELETE table FROM ( SELECT MAX(id) id, field FROM table GROUP BY field ) temp_table INNER ...
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42 views

Select SQL_Calc_Found_Rows query extremely slow

I'm Wordpress 4.2.2 on an Ubuntu 14.04 LTS server, with PHP 5.9x and MariaDB 10.0.17. When clicking on a post on my site I see many slow queries that all resemble this and it ends up taking as 8 or 9 ...
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28 views

Delete using join or using sub-query?

I need to delete rows from a table based on what is present in a temporary table. For me, both of these statements work : DELETE from main_table where `id` in (select `deletable_id` from ...
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0answers
59 views

Query execution taking long time

SELECT sqltext.TEXT, req.session_id, req.status, req.command, req.cpu_time, req.total_elapsed_time FROM sys.dm_exec_requests req CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS sqltext select ...
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109 views

INSERT INTO with TABLOCK taking longer than without TABLOCK [closed]

I'm doing something like below to ensure the insert is minimally logged: insert into AnotherDatabase.dbo.HeapTable with (Tablock) ( <column fields ) select <column fields> from ...
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74 views

How to speed up for huge tables in SQL select query?

I have the following huge tables. Table_1 with 500000 (0.5m) rows Table_8 with 20000000 (20m) rows Table_13 with 4000000 (4m) rows Table_6 with 500000 (0.5m) rows Table_15 with 200000 (0.2m) rows ...
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0answers
50 views

Postgres not using the index even when rows returned is 5% of the table

I have a postgres table with the following structure: +---------+-------------+-------------+----------+---------+---------+ | id | timestamp | numvalues | text1 | text2 | text3 | ...
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1answer
53 views

Why MySQL SELECT performance depends on table size? [closed]

I've got two identical tables with the following structure: CREATE TABLE words ( id bigint(20) NOT NULL, `text` int(11) NOT NULL, w1 int(11) NOT NULL, w2 int(11) NOT NULL, w3 int(11) NOT ...
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0answers
66 views

Most effective way to manage a growing list of time series data in an MS Access database

I am building a database to store time series data along with some other summary statistics. Since this is a local application I do not have access to more robust database solutions and am confined to ...
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0answers
43 views

PostgreSQL DB freezes with large inserts

I am developing a web application with an SQLAlchemy ORM linked with PostgreSQL database backend. I have this usecase where a client uploads a file of about 20 MB containing large data. What I am ...
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69 views

Query Performance - Why is a query slower when there are two criteria on the same column?

I have these two queries against a view, where I've added WHERE clauses against a date column (Indexed, Unique, Non-Clustered, Ascending): SELECT ColA FROM MyView a WHERE a.[Date] >= ...
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1answer
157 views

MongoDB document size for collection - impact on RAM and query performance

I have been advised on stackoverflow to ask this question on dba.stackexchange instead - We are using MongoDB version 3.0 with WiredTiger storage. As newbies to MongoDB, we may have designed our ...
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0answers
57 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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0answers
42 views

Poor performance filtering mysql spatial join

First of all, sorry for the crossposting. I ask this question in stackoverflow and they sent me here I have a mysql table with spatial references (GEOGRAPHIC_FILTER), like cities, countries, natural ...
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48 views

MDX query is SLOWER with warm cache

I have a MDX query that executes faster on cold cache than warm cache. If I ran the same MDX query after restarting SSAS it takes 14 seconds. All subsequent runs of the same statement then take 50 ...
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124 views

Simple avg query on large table much slower in PostgreSQL than SQL Server

I have a database with three tables items, parameters and measurements in both servers and want to query the measuerment table. But the query is much slower in PostgeSQL (9.4) vs SQL Server (2012). ...
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27 views

Sampling and matching samples with spatial conditions

The Problem I have two tables with start points of a route and possible end points of a route which need to be matched against each other. I also have a given distribution for the distance between ...
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1answer
59 views

Mysql Partitions with Partition limit

I have a partition table on basis of Primary key having 1.5 Billion rows in it. But when i check ibd files only 80 ibd show in GB's whereas 120ibd shows 1MB file. I would like to know how does the ...
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1answer
622 views

Optimizing Amazon RDS - MySQLTuner Recommendations / Feedback & Suggestions

I'm currently trying to optimize a database I've inherited for speed. The server is an Amazon RDS db.m3.large instance: 2 VCPUs 7.5 GB Memory 500 GB HDD My current strategy is to do the ...
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0answers
94 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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27 views

How to query against legacy data that needs to be cleaned up?

I have an existing SQL Server DB with 3 tables (note: this is a made up example, but modelled after a real problem). Artists : contains music artists MusicRecords : contains information on music ...
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47 views

Is it bad practice to launch more than 100 sql statements at once?

I have PHP code that is meant to updating the billing status of someone. I only want it to update if the bill has been successfully created and therefore I think a possible solution would be to ...
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1answer
197 views

SQL Server 2012 stored procedure runs very slow sometimes

I have a stored procedure with a single large query which takes an ID as a parameter and returns some counts. It has quite a few inner joins and left outer joins but they are all on indexes. The ...
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50 views

Is there any way to improve this code?

SELECT tblstud.studid, tblsched.ip FROM tblstud LEFT JOIN tblstudsched ON (tblstud.studid=tblstudsched.studid) LEFT JOIN tblsched ON (tblstudsched.schedid=tblsched.schedid) ...
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36 views

Can MySQL Index Merge an Composite index with a single column index?

I am tuning a query and currently have an index as following : Index 1 : (col1, col2) An example query would be : SELECT * FROM t1 WHERE col1 = '1' AND col3 = '2'; I have created an index on ...
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35 views

Best ratio for files and file groups for a highly partitioned table

I have a number of tables with exactly 1000 partitions. Each table can be up to 200G with 100M rows and cannot be compressed. Data in partitions distributed quite equally. The SQL Server has 8 ...
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1answer
28 views

Create a log file for check which time import has been done and to split the import files

How to create a log table for when does the last import has been done and also for Query for split the records in to 1000 while importing. to avoid the bulk insert For example : If the data ...
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1answer
428 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 ...
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1answer
68 views

optimizing query for slow queries

I have this query in my slowqueries table which essentially is taking about 5-8 seconds to complete the query time: SELECT s0_.id AS id0, s0_.updated AS updated1, s0_.created AS created2, ...
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1answer
43 views

Mathematical or Computing Alternatives for MySQL Combination Queries operating toward their Performance Limit

We regularly run a contest that is becoming quite popular. In the contest, we need to select the combinations of contestants from 8 groups whose cost is under a threshold, and who combined have the ...
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110 views

SQLServer dependency graph and performance

I have a large stored procedure running on SQLServer2008 to produce a report on the previous day's data. It rehashes data from 12 tables, including a lot of ORDER by date and CASTS. Among others, it ...
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69 views

Odd Execution Plan

I have a table in SQL Server that is performing very slowly and I have been trying different indexing options to try to speed it up to no avail. I suspect all of the varchar(max) fields may be a ...
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1answer
53 views

How much should I care about prepared statements for simple queries?

I wonder how much I should care about prepared statements (and therefore try to optimize my code) in case of pretty simple statements. The question originates from the fact that I recently noticed ...
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0answers
68 views

How to use join with this query? [closed]

This query is working fine, and giving the right result. In this query all columns are in one table, but now I have made some changes. Now columns named Semester and Major are in different Table ...
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0answers
49 views

Copying to tmp table slow for query … but only sometimes

I have a query, and I admit it may not be the prettiest query in the world. Sometimes this query runs fairly fast (e.g. 200ms) and other times it runs super slow (e.g. 30s). I don't know why, and ...
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1answer
59 views

pt-query-digest results are empty

I have a slow log generated by MySQL 5.1.71-log, that I've copied onto another machine. It appears I'm not getting any results from pt-query-digest. $> pt-query-digest slow.log # 2.1s user time, ...
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1answer
127 views

Complicated data

I have a requirement i got from my father. He gave me a table and wanted me to digitalis it. So that he can the system can do all the dirty jobs for him ( that's why there are developers in the world, ...
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0answers
26 views

Why do these two queries (which I think are equivalent) rely on different keys?

We have a query that we don't like, since it ends up doing a full table scan. EXPLAIN SELECT count(*) AS c, location.name FROM study LEFT JOIN location ON study.location_id = location.id ...
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93 views

Is it best practice to include partition keys within foreign keys when referencing partitioned tables?

The large tables in our database are partitioned by an id in order to separate data and speed up IO. The table of the data is partitioned by the partition key, but the primary key is only on an ...
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0answers
59 views

Slow compilation of a SQL statement

I have SQL Server 2014 and a large table (more than 200Gb) with 100M rows and more than 300 columns. For one "unpivot" query I wanted to see its estimated execution plan and it took more than 90 ...