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

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3
votes
2answers
288 views

Query planner thinks doing a sequential scan on a very large table is faster than using an index?

I've got a query that selects the most favorited photo for each of the last 12 editions for a particular domain (this is just a segment of a larger query, but the problem seems to stem from here): ...
0
votes
0answers
5 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 ...
3
votes
2answers
369 views

SQL server query is slow *without* including execution plan

I have just set up fresh installation of SQL Server 2012 on a new server and I'm experiencing very strange performance problems. Long story short, for some reason not including execution plan makes my ...
0
votes
1answer
48 views

Optimizing intersect query in MySQL

I'm facing a performances problem in our MariaDB server. We have a table linking users to pages, a user belongs to 1+ pages. I have a page that have users and I want to get the 10 best pages based ...
1
vote
1answer
327 views

Different thread states in query execution

My MySQL 5.1 based Intranet system is facing very bad performance during high load. When observed through MonYog, I found below thread states: We can simply understand the different thread state by ...
0
votes
0answers
16 views

Slow Query Performance - Can't Debug

I have a MySQL query that I am trying to debug the performance issue but cannot. I know that the majority of the query is reading/processing rows (Sending Data state). However, in the explain output, ...
2
votes
0answers
24 views

Grant users privilege to use QUERYTRACEON 9481

Microsoft suggests using OPTION (QUERYTRACEON 9481) for queries that have "degraded" performance against SQL Server 2014 databases running under compatibility level 120. In my situation, "degraded" ...
1
vote
0answers
15 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 ...
1
vote
1answer
25 views

Best approach to get last value inserted

I have several devices that report via Edge network their position (and more data) to a UDP server which directly inserts this data in a SQL 2008 r2. I want to know which is the best approach to ...
1
vote
1answer
59 views

Indexed View - how to verify if it is worthy?

I have the following indexed view: CREATE view VProcessStatus WITH SCHEMABINDING AS select processstatus, StatusCount = COUNT_BIG(*) FROM DBO.tbltaxtransaction GROUP BY ...
1
vote
1answer
17 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 ...
0
votes
2answers
773 views

How to fix slow LIMIT queries with big offsets without heavily rewriting them?

Imagine a very basic example of your average discussion board. For example: CREATE TABLE threads ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, title VARCHAR(100), PRIMARY KEY (id) ) CREATE ...
1
vote
1answer
185 views

How can I use mongoDB efficiently in this scenario?

I'm trying to build a system of documents that have hundreds of tags assigned to them, but each document-tag association has a certain condition it has to also meet so the document would be returned: ...
2
votes
1answer
113 views

Minimizing Page Fetches

I have a complicated database structure and am trying to use it to retrieve Records based on multiple selection criteria from several tables. As a general rule, is it better to attempt to use ...
1
vote
1answer
29 views

What are the side-effects of disabling nested loops in postgres?

A query of multiple joins spends a lot of time on nested loops. I disabled the nested loops and the query ran much faster. However, I have been told that nested loops might give me wrong results by ...
0
votes
1answer
85 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, ...
1
vote
2answers
372 views

Query Performance Tuning on a huge table

I have the following table Transactions. The table looks like this: CREATE TABLE [dbo].[Transactions]( [TransactionID] [bigint] IDENTITY(1,10) NOT NULL, [PlayerID] [bigint] NOT NULL, ...
0
votes
2answers
61 views

Does it make sense to order condition in where query?

We have a clustered index in table Tbl with order of A,B,C. Does it make senses to write a query to have WHERE A = @a, B = @b, C = @c or it'll be as same as WHERE C = @c, B = @b, A = @a Does the ...
1
vote
1answer
3k views

statistics State in MySQL Processlist

I have a busy MySQL Server having query SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION ...
0
votes
1answer
32 views

large SQL Performing quite slow (roughly 2 seconds for 290 rows) when having to deal with entries that can be NULL

SELECT version_stamp, pscdesc_id, psc, pscdesctext FROM pscdesc_history WHERE ( psc IN (SELECT psc FROM pso_history AS c ...
0
votes
1answer
2k views

Select from a list of values from JSON encoded data

I have saved the details of the product in JSON format. I am wondering how to select from a list of values from a "JSON_ENCODED DATA" For Example I want to select TV with screen_type as LED or LCD. ...
0
votes
0answers
36 views

Querying really slow Postgres

I have multiple tables on Postgres wit GIS and when I query SELECT * FROM rxmsg JOIN Vehicles ON rxmsg.vid=Vehicles.vid JOIN stops on ST_DWithin(rxmsg.point, stops.point,1000) JOIN drivers ON ...
0
votes
1answer
603 views

Improve MySQL Query Performance - Too many records

I am using MySQL RDMS for a contact management system. Now a days my database grew in size and contains more than 1 million records. Checking duplicate phone numbers became a big issue during ...
0
votes
2answers
123 views

View with left joins are very slow

I have a view based on join of 3 tables and and query on view is taking 10 mins to fetch the results. Can anybody help me in reducing the time taken to fetch results? VIEW CREATE view ...
1
vote
1answer
118 views

Estimated rows very wrong when using declared variables

I am getting very, very wrong estimates for the clustered index seek step of this query (estimated rows is 8,637,530; actual is 74,723): Declare @StartDate as date = '10/1/2014'; Declare @EndDate as ...
2
votes
2answers
257 views

Slow queries on billions-rows-table // index used

Since I'm a young developer and not really skilled in using databases (PostgreSQL 9.3) I ran into some problems with a project, where I really need help with. My project is about collecting data of ...
0
votes
0answers
31 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 ...
0
votes
1answer
91 views

Rerunning query in the same connection takes significantly longer

I am having a weird issue when a running a query that joins some semi-large tables (one table is about 2 million rows and the other about 21 million) together. What happens is the query does not run ...
0
votes
4answers
39 views

Single SQL query to retrieve data in a particular order (not ASC/DESC)

I have a MySQL table, let's say called reviews review_id, product_id, language_id, rating, review, author language_id ranges from 1 to 10 for 10 different languages. Let's say I determine that my ...
-1
votes
1answer
17 views

PDO over network, hangs MySql Database after running 1 to 3 hours? [on hold]

I have the following class --------------------------------------------- CRUD Code Snippet-------------------- class CRUD{ function __construct(){ $this->db_user = "user_name"; ...
1
vote
1answer
78 views

Mysql join table order by index

First Master Table CREATE TABLE `edipostingmaster` ( `ID` bigint(20) NOT NULL AUTO_INCREMENT, `applied` int(11) DEFAULT '0', `fileName` varchar(255) DEFAULT NULL, `checkNo` varchar(100) ...
0
votes
1answer
51 views

How database buffer pool work?

For example we have 2 scenarios: Scenario 1:- We have very small buffer pool size of 100MB. My query data is 500MB. Does the system keep 500MB query data in RAM such that a new ...
0
votes
2answers
2k views

Optimize IN clause in where query with order by - MySQL

I am trying to optimize a query that using IN clause in WHERE to avoid file sorting. To make it easy , I created the following sample which shows the problem. Here is my query: SELECT * FROM `test` ...
0
votes
1answer
72 views

MySql: Slow join and group by on indexed columns

The following query takes 15-20s to run SELECT "Trade_US"."ID" AS "Trade_US.ID", "Server_US"."Name" AS "Server_US.Name", "Trade_US"."TradeTypeID" AS "Trade_US.TradeTypeID", "Users"."ID" AS ...
2
votes
0answers
32 views

select on table slows done during update on same table [closed]

I have a weird problem with mysql. During a transaction which runs from 10-30s around 270 statements are performed, some of which are updating and inserting a few rows on a table. If a select is ...
0
votes
1answer
115 views

How to optimize query

using SQLite3 and the following query, it seems like there should be a better performing way to write this query? Is there? Select Name, Sum(Case When Used Is ...
2
votes
1answer
34 views

How can I speed up an sql query that round trips between two tables

I first posted this question on stackoverflow, and now I see this site, seems more relevant. These tables are not that big, but the time taken to process this query is long. What can I do with the ...
3
votes
1answer
53 views

Help with indexing narrow table with many millions of rows

I have a good amount of experience with SQL Server, but not much with indexes and I fear I'm a little bit out of my depth in trying to figure out how to correctly structure a table that has 100+ ...
0
votes
1answer
46 views

Columns count in SELECT query and SQL Server buffer cache

Let's assume that I have a table with 30-50 millions records. It has ~40 columns. Currently when I request data it always requests all columns because of legacy ORM that we use. I know that if we ...
0
votes
1answer
77 views

Tuning Mysql and Monitoring

I would like to know if anybody can point me towards a tool/way for MySQL database tuning ... Actualy the tunning of my.cnf is like below My database is in MyISAM | Mysql 5.1.73 key_buffer = 500M ...
2
votes
2answers
217 views

SQL Server - Logical Reads lowered, Execution time remained the same

A view executed Select columns from view where col= "date range" (view contains calculation in it Col1+Col2*col3 AS Col4). It took 7 seconds for 500K rows to return, logical reads some 144k. Added ...
0
votes
1answer
16 views

Query Performance Regression Between Different Versions

I have two MySQL databases, A and B. They have identical hardware and schema. They have different data and database A has more data then B. Database A is also running version 5.1, while B is on 5.5. ...
1
vote
2answers
908 views

Find nearest values from MySQL Table

I want to fetch nearest rates for a given value from below table. mysql> select * from rates; +------+----------+----------+ | ID | Type | Rate | +------+---------------------+ | 1 | ...
4
votes
4answers
677 views

optimizing a compare query

Suppose I have two tables, A and B, and I know that size(A) = size(B). I want to confirm that the data in both tables is the same in three given columns, suppose they are X, Y, and Z (there are no ...
5
votes
3answers
4k views

Is it better to separate a big query into multiple smaller queries?

There are situations which require having really big query joining several tables together with sub select statements in them to produce the desired results. My question is, should we consider ...
-1
votes
0answers
42 views

Performance issue when we directly insert into #temp table

It might be silly one but I am new to query optimization so I want to know the which query has the better performance select * into #temp from MYTable or Create table #temp ( \\same ...
2
votes
1answer
129 views

Best Indexing Strategy for Query with Equality[A], Range[B], Group By[C], AND Order By[count(P)]

I have a poorly performing query: SELECT user_id, count(item_id) as count FROM table items WHERE category = 'magazine' AND created_at > 1384754400 GROUP BY user_id ORDER BY count(item_id) desc ...
1
vote
1answer
79 views

Slow SQL Server authentication, but fast SAN, fast querying?

I am asking you after days of research but I think I don't have required skills to understand what is happening. I have a slow authentication on a SQL Server 2008R2, which leads to a timeout for the ...
0
votes
0answers
32 views

Performance decline function vs command window

I have a function that I first wrote as a serious of commands. In the SQL command window when executed, those steps take about 8 seconds to return the data set. When those same commands are turned ...
1
vote
3answers
35 views

MySQL select with between optimization

I got issues with some geo IP query. So basically here is create code of table: CREATE TABLE `geo_ip_city` ( `id` INT(5) UNSIGNED NOT NULL AUTO_INCREMENT, `begin` BIGINT(20) NOT NULL DEFAULT ...