A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.
1
vote
1answer
48 views
Algorithm for finding the longest prefix
I have two tables.
First one is a table with prefixes
code name price
343 ek1 10
3435 nt 4
3432 ek2 2
Second is call records with phone numbers
number time
834353212 10
...
0
votes
2answers
75 views
How can I increase performance for select in select statement
The item table is like this
id category_id name registered
I have to show total number of items from the beginning. Suppose between 2013-05-01 to 20-05--05, I have to count all the items ...
-1
votes
4answers
73 views
Dropping and recreating indexes [closed]
I most often come in a situation where the users move there database from one server to another and immediately after they move they face performance problems(slowness).
I somehow manage to rebuild ...
0
votes
0answers
29 views
Properly index magento mysql tables to improve specific query performance
I am running magento community edition and its db performance is horrible. I have the following query:
SELECT `width_idx`.`value`, COUNT(DISTINCT width_idx.entity_id) AS `count` FROM ...
-2
votes
1answer
59 views
what's the fastest method to export a table through sql query ? 11g - performance
I'm connected to the oracle server remotely. I need to export a table data(the whole table) with millions of records but due the hosting restrictions I can only use SQL (no exp , expdp) . Therefore ...
0
votes
2answers
66 views
How do I use subquery on the same table in MySQL?
I have a query like this which takes a really long time to run. The table is around 4 million rows.
DELETE FROM TABLE WHERE value_was IS NULL OR value_was <= value_now;
I'm hoping I could ...
3
votes
3answers
86 views
How can I improve this query?
About a year back I introduced a query which returns a sort of "Customers Also Purchased" data-set. At the time it ran reasonably fast however, as of late it's become very slow, sometimes taking up to ...
0
votes
0answers
84 views
how to find similar word with more similarities
how to Find words with length less than or equal...
declare @inp nvarchar(max),@data nvarchar(max)
set @inp='You can dance, you can jive, having .... jove... jve, ...'
set @data = 'jeve'
...
0
votes
2answers
62 views
How to use and optimize subquery on 100 million rows
What I'm trying to do is running a job on more than 100 million domains which haven't processed before.
I have two tables, "domain" and "domain_setting", on every batch (10.000 domains per batch) I'm ...
2
votes
2answers
103 views
Is there a difference in performance between @date and getdate()?
Usually I use the getdate() function in my where clauses to go back in time.
Something like:
DOC.DATUM >= DATEADD(DD,-1*SSN_SDO.DANA_ZA_POVRAT,GETDATE())
Will SQL Server 2008R2 perform faster ...
2
votes
3answers
105 views
How can I query data from a linked server, and pass it parameters to filter by?
I have a really big query that needs to be run on multiple databases, and the results appended to a temp table and returned.
The basic syntax looks something like this:
INSERT INTO #tmpTable (Id, ...
1
vote
1answer
61 views
Query optimization when no row is returned
I am using explain to figure out what is happening in my query which is:
explain select t from c where u1_id = 1 group by t;
I see "Using where" in the Extra column of the resultset. But this only ...
0
votes
1answer
35 views
Optimizing Query
Can anyone help me tuning this query.....
explain extended
SELECT DISTINCT a.msisdn FROM `std_msc_opr_wise` a
LEFT OUTER JOIN
(SELECT msisdn
FROM as_treat_pre_usage_30days
GROUP BY ...
0
votes
1answer
92 views
What is the correct model for related tables with millions of rows?
I need to create a question and answer tables that will have millions (maybe billions) of rows.
The current model is:
Question Table
id_question (PK, auto increment)
id_user
question_content
...
0
votes
0answers
56 views
SQL nested select (query rows after variable), running slow
Have large table (Sybase) rows = 6276225. I'm pulling call status and my query is very slow.
In effect what I’m trying to do is pull data for any event after my variable. While querying for just one ...
0
votes
1answer
37 views
MySQL stored routine performance while using PREPARE
Instead of maintaining stored routines for each database in my current environment I have decided to create separate database just for stored routines storage. Mainly I am using them for reporting. ...
0
votes
1answer
20 views
Simple query not using indexes
My query is not using indexes.
It is a simple query.
Can someone explain why that's the case?
The query:
select TIME_FORMAT(start_time,'%H:%i') start_time,
TIME_FORMAT(end_time,'%H:%i') ...
2
votes
2answers
94 views
Different queries result in big difference in performance
I have 2 similar functions, different way result in big diff in performance.
The PostgreSQL version: 9.2.1.
Function 1
create or replace function func_1() returns text as
$$
declare
v_i ...
0
votes
1answer
49 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 ...
4
votes
3answers
224 views
Query runs slow in test site on first execution. Why?
I found this query by watching a test site with sql profiler for anything taking over 10 seconds. I plopped the code right out of sql profiler and into sql studio, where it was able to execute ...
4
votes
2answers
130 views
Is high Extent Fragmentation a problem?
DBCC SHOWCONTIG scanning 'MyTable' table...
Table: 'MyTable' (2048062382); index ID: 1, database ID: 28
TABLE level scan performed.
- Pages Scanned................................: 1019182
- Extents ...
3
votes
1answer
102 views
How does order of index affect performance in SQL Server?
I am wondering how does order of index affect performance (ASC, DESC) ? If it affects, why ? And which order should I choose ?
0
votes
1answer
61 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 ...
0
votes
0answers
19 views
Identical Postgres index scan taking 5x longer on server
I have an intermediate table for managing a many-to-many relation between tables called Expert and Subject:
Column | Type | Modifiers
...
0
votes
1answer
76 views
speeding up a query on MySql
I have a table with more than 10 million rows and 10 fields(columns). There is an index on field_1 and I am running the following query.
create table t2
select field_1,
sum(ifnull(field_2,0)) ...
3
votes
1answer
90 views
Could too many idle connections affect PostgreSQL 9.2 performance?
Some queries on my database server seem to take a long time to respond, and I believe the CPU usage is high. When running ps aux, I see ~250 "idle" connections (which I believe to be too many). I ...
2
votes
1answer
205 views
How to speed up queries on a large 220 million rows table (9 gig data)?
The issue:
We have a social site where members can rate each other for compatibility or matching. This user_match_ratings table contains over 220 million rows (9 gig data or almost 20 gig in ...
6
votes
2answers
23 views
Postgres performance difference on insert
I was tried to partition one large table, and come with such Postgres behavior that I could not explain. Maybe you will have any suggestions?
I went quite straight forward way (i know that it is not ...
6
votes
4answers
308 views
Gaps and islands: client solution vs T-SQL query
Can a T-SQL solution for gaps and islands run faster than a C# solution running on the client?
To be specific, let us provide some test data:
CREATE TABLE dbo.Numbers
(
n INT NOT NULL
...
4
votes
2answers
137 views
Inner join using an array column
Having trouble indexing and executing a query in O (log n) time.
The query includes an INNER JOIN, an ORDER BY, and an equality operation. If I understand the laws of databases correctly, a query can ...
2
votes
1answer
37 views
What is the algorithmic complexity of a PosgtreSQL greater than or lesser than index query (compared to equality)?
Assuming there is an index idx_int on an int_col column, what is the algorithmic complexity of a query like this?
SELECT id FROM table
WHERE table.int_col > 1;
I'm specifically interested in ...
0
votes
2answers
159 views
optimize big sql query
My query has to return a statistics for example for march containing productname and price and its sidedishes (1:n relation) with the right price of each sidedish and the right tax for each sidedish ...
0
votes
1answer
62 views
Speed efficient query for membership first joined, latest category from membership table (min, max)
I have the following table representing membership information:
CREATE TABLE IF NOT EXISTS `membership` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`organisation_id` int(11) NOT NULL,
...
6
votes
1answer
185 views
Landed as BI, but databases are a big WTF, what to do?
Maybe a duplicate, but I believe my case is a bit different. From one of the answers I got to this post on SQL Server Central that also comes handy too but is not quite the same scenario: 9 Things to ...
1
vote
1answer
87 views
SQL Server 2008 search joining query
I have two table as one is the message table and another one is messageUser table.
Now i need to check before insert a new row.
for example,
M_MessageMessageId=========
...
0
votes
1answer
76 views
Second time query execution using different constants makes faster?
Can someone explain or direct me how execution on indexes happen with different constants at intervals in Mysql. I notice only for the first execution on the table it takes time, after that with ...
2
votes
1answer
90 views
Oracle: How to gather stats in a logical standby database?
I have a Primary and a (logical) Standby Database. The Schema 'APP' gets synced.
Now a User has performance issues running a query against some tables in this 'APP' schema of the Standby Database. On ...
1
vote
2answers
76 views
Database and query optimizacion
I have a database containing three tables: tbl_database (main table is the primary), tbl_cmdatabase and tbl_blacklist. The three tables share the same structure but differ in the number of records ...
0
votes
1answer
80 views
Looking for performance improvements for this query
This query is taking a long time to execute. We are expecting results in 0 sec, if possible.
Please help me to do any other following:
Rewrite the query
Suggest any indexes
Any other optimization ...
1
vote
0answers
89 views
SOLVED: Postgres 8.4.5: Bad query plan vs Good query plan when changing date range on large data table
SOLVED.
I was able to resolve this issue by altering the time.date column to allow 1000 stats: ALTER TABLE time ALTER COLUMN date SET STATISTICS 1000;
Now the queries are running very fast, down to ...
0
votes
2answers
121 views
MySQL: can not get rid of “Using filesort” in a simple query
Simple query but can not get rid of "using filesort":
CREATE TABLE IF NOT EXISTS `online` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`uid` int(11) NOT NULL,
`expiration` int(11) NOT NULL,
...
2
votes
3answers
180 views
Why is SQL running the same query longer from another connection?
Here is the issue overview: Why does my stored procedure run faster when executed localy vs remotely?
Dont jump to any conclusion just yet, let me explain what I mean...
Here is the setup:
A Windows ...
3
votes
2answers
390 views
PostgreSQL Sequential Scan instead of Index Scan Why?
Hi All I've got a problem with my PostgreSQL database query and wondering if anyone can help. In some scenarios my query seems to ignore the index that I've created which is used for joining the two ...
4
votes
1answer
64 views
Covering Index Question
I have the following query
Select Pt.PRODID, PT.INVENTREFID, Inv.ItemName, PT.ItemID, Configid, Pt.QTYSCHED,
PT.DLVDATE, Pt.CREATEDDATETIME, pt.SCHEDEND,
CASE Left(PT.INVENTREFID, 3)
WHEN ...
0
votes
2answers
159 views
Large time difference between two almost identical simple queries…why?
I'm trying to understand why is there so much difference in execution time and CPU usage between two simple queries that only differ in a computation. The queries are the following:
SELECT ...
2
votes
0answers
32 views
How can one improve the performance of a query that selects on a low cardinality column in MySQL?
I have a "State" column that has a low cardinality (three possible value), on which most of my queries perform an equality selection (WHERE col = 'blah') AFAIK you need something like a bitmap index ...
0
votes
1answer
74 views
Mysql. Block/disconnect slow queries
I am experiencing issue.
Someone 'attacked' my server: simply by searching the same phrase with multiple requests.
As it is text search request and database indices are not used, the engine searches ...
13
votes
4answers
473 views
Why would I NOT use the SQL Server option “optimize for ad hoc workloads”?
I've been reading some great articles regarding SQL Server plan caching by Kimberly Tripp such as this one:
http://www.sqlskills.com/blogs/kimberly/plan-cache-and-optimizing-for-adhoc-workloads/
Why ...
0
votes
1answer
117 views
slow queries - set weight to token type in tsquery - postgresql
Postgresql version 9.2.3!
I'm working on a database for mapping of chemical names. My main table contains aprox 91 million records and it's indexed by gin. I want to query it with multiple names (I'm ...
0
votes
1answer
48 views
Faster joining on 'most recent' related rows
I have a bug tracking application. The bug table stores very little,
because every state change to a bug happens by adding a comment. For
example, the current state of a bug is determined by the state ...
