An evaluation of whether a system works well enough to be fit for purpose. Normally performance refers to the speed with which a system completes an operation or set of operations over time.

learn more… | top users | synonyms

0
votes
2answers
60 views

Proportion of MySQL variables

I made some research on MySQL performance. After doing some tests and verifyed the improvement, (thank you guys) I end up asking myself: "Is there any formula or metric between groups of variables?" ...
1
vote
3answers
2k views

Oracle query is slower the second time

I have a general question about something I'm seeing in performance tuning in Oracle. I have a query that I'm testing. It's too big and complex for me to provide a simple example, sorry! (I tried ...
0
votes
1answer
27 views

What is less time costly?

I'm migrating a database from DB2 to MySQL. There are big tables, so it takes a huge amount of time. The question here is: If there's a table with about 9 millions of records with InnoDB storage ...
5
votes
4answers
2k views

How can I speed up “show columns” on MySQL?

My application depends on running "show columns" for certain tables. It takes about 60ms to run, whereas all our other queries take under a ms. Querying information_schema directly is even slower. ...
0
votes
0answers
43 views

mysql eating RAM without queries?

Somehow MySQL eats up 50% of my RAM on the server being used. I checked and there are no queries, show full processlist is empty. I restarted the mysqld and within a couple of minutes the RAM usage ...
2
votes
1answer
40 views

How should a numeric value that is an external key be stored?

This is something I was pondering recently. trying to determine how to store certain values. The best wide spread example I can think of is Federal Employee Identification Number - more commonly knows ...
2
votes
1answer
282 views

Scaling PostgreSQL TRIGGER(s)

How Postgres triggers mechanism scales ? We have a large PostgreSQL installation and we are trying to implement an event based system using log tables and TRIGGER(s). Basically we would like to ...
0
votes
0answers
30 views

PostgreSQL slow update -> does autovacuum have anything to do with it?

I am quite new to PostgreSQL as I only need it to create a map (using PostGIS). So I don't really know on hot how to optimise my DB... I have a table with a lot of polygons that I'd like to save in a ...
1
vote
2answers
2k views

Is SQL*Net message from dblink > 30% a performance issue?

I have a Java web-application running under Glassfish. App accesses Oracle using JPA (eclipselink). Last 2 days I'm observing some perfomance issues: some messages about long running queries (10 to ...
2
votes
1answer
144 views

PostgreSQL 9.x: a clustered index on column A is the same as creating a table ordered by A?

Reading the official PostgreSQL documentation for version 9.0 I read an interesting escamotage that performs better than CLUSTER for big tables: The CLUSTER command reorders the original table by ...
7
votes
1answer
591 views

Why adding SQL Server user to “Perform volume maintenance tasks” improves the speed of database resizing so much?

If I want to create 5GB database with CREATE DATABASE [test] CONTAINMENT = NONE ON PRIMARY ( NAME = N'test', FILENAME = N'E:\2012\test.mdf' , SIZE = 5529600KB , FILEGROWTH = 1024KB ) LOG ON ( ...
0
votes
0answers
51 views

Very high CPU caused by mysql service

A running mysql service uses CPU in a crazy way. (See attached screenshot from htop) I followed the instructions here with no luck. My server specs: CPU: 1900Mhz . Intel Hexa-Core Xeon E5-2420 ...
2
votes
1answer
4k views

Why is my Amazon RDS instance so slow?

I currently run a Windows Server with SQL Server Express. I'd like follow best practice and separate the application from the database, so I've created an RDS instance and exported my database. ...
4
votes
3answers
1k views

Keeping default max memory 2147483647 MB value in SQL Server, a bad practice?

Based on that msdn page : server memory settings it's a good practice to keep the default values for SQL-Servers min and max memory to keep it dynamic... From what I learned through tutorials you ...
1
vote
1answer
40 views

How compiled are prepared statements?

I found this explanation of how prepared statements are compiled, but I'm still unsure. What exactly is "compiled" in the context of a prepared statement? Is a C compiler executed to create a custom ...
1
vote
2answers
55 views

Should I normalize my string arrays, or just keep it a simple string?

I am working on a project involving cards from the Magic: The Gathering game. To be of any use, I must load the basic information about each card into my database, but some of the fields may contain ...
-4
votes
1answer
52 views

Create database unique Surrogate Keys without using GUID’s

What is the best way to get database unique surrogate keys in Microsoft SQL Server when using something like “auto increment” as opposed to GUID's. The purpose is to increase performance over using ...
6
votes
1answer
2k views

How to improve Procedure Cache Hit Ratio?

From what I can tell Procedure Cache Hit Ratio below 95% is a problem. On my box, the values hover from 85 to 95%. How do I fix this issue? The server seems to have plenty of RAM so that ...
3
votes
2answers
333 views

Should I use a compound or surrogate PK in a many-to-many table?

I have a database: DROP TABLE IF EXISTS `books`; CREATE TABLE `books` ( `isbn` VARCHAR(255) NOT NULL, `title` VARCHAR(255) NULL DEFAULT NULL, PRIMARY KEY (`isbn`) ) COMMENT 'Books used at this ...
0
votes
1answer
61 views

Best query to exclude existing friends from query

I have a User table / id_user / username / .. friends table (pair AB and BA): / friend_of / friend_to and a friend_request table (used for pending friend requests) / id_req/ sent_from / sent_to ...
1
vote
0answers
115 views

Postgresql: Partition table by hour

I have a system that inserts several million records over the course of 24 hours. Users don't care about the data that's older than 24 hours, and typically query data over a small time frame (5 to 60 ...
3
votes
1answer
1k views

Optimizing large database query (25+ million rows, using max() and GROUP BY)

I'm using Postgres 9.3.5 and I have a large table in the database, currently it has over 25 million rows and it tends to get even larger rapidly. I'm trying to select specific rows (all unit_ids with ...
1
vote
2answers
398 views

Is there a faster way to get UNION ALL behavior in Postgres?

I have a table (t0), in my Postgres DB, with data that looks something like this: t1_id t2_id 1 1 2 1 2 1 4 null 4 null 5 null And I have a query to return my ...
0
votes
2answers
138 views

Make DB tables customizable from an Admin

I want to build an commercial product promotional mobile application in which the administrator of the app will be able to customize some texts / pictures or whatever from the database that ...
4
votes
1answer
1k views

need suggestions to improve view performance

I am looking to improve the performance of a view in SQL Server 2008. This view exists in a reporting database that is widely used by not-very-technical-folk to basically denormalize all of these ...
1
vote
4answers
108 views

with MySQL, are multiple single column indexes faster than one multi-column index? [closed]

I have a performance related question, in MySQL, are multiple single column indexes faster than one multi-column index?
11
votes
2answers
4k views

How to create an index to speed up an aggregate LIKE query on an expression?

I may be asking the wrong question in the title. Here are the facts: My customer service folk have been complaining about slow response times when doing customer lookups on the administration ...
3
votes
1answer
130 views

Biggest wait WriteLog

I have been given a server (SQL Server 2008R2 64 bit) where our application is running. There has been a gradual decrease in the performance of the application. Now it has come to a point where ...
11
votes
1answer
5k views

Index optimization with dates

I have a large table of objects (15M+ row) in PostgreSQL 9.0.8, for which I want to query for outdated field. I want to divide the query by millions, for scalability & concurrency purposes, and I ...
4
votes
1answer
71 views

What is the performance impact of queries against DM objects using DMVs in SQL Server 2008?

Recently, I've been running queries against our production system on the DMVs for querying the plan cache. In particular, here's the from clause of the query: FROM sys.dm_exec_cached_plans AS cp ...
0
votes
1answer
53 views

Get statistics of slow running queries

My database application runs many different queries. I have set log_min_duration_statement to 1000. But queries logged there are not always slow, most times they just take a few ms. Is it possible to ...
7
votes
2answers
21k views

SELECTing multiple columns through a subquery

I am trying to SELECT 2 columns from the subquery in the following query, but unable to do so. Tried creating alias table, but still couldn't get them. SELECT DISTINCT petid, userid, (SELECT ...
-1
votes
1answer
42 views

Query optimization and takes less execution time

CASE-1: SELECT * FROM A JOIN B ON B.CustomerID=A.CustomerID CASE-2: SELECT * FROM A JOIN (SELECT * FROM B) C ON C.CustomerID =A.CustomerID Which CASE is efficient ?
0
votes
0answers
58 views

MYSQL : Copying to TMP table nightmare

I'm having a (AFAIK) random issue. My server is MySQL and I have a query that is sometimes 10000 times slower as you can see on this screensot : http://snag.gy/vJJ39.jpg The long time occurs during 2 ...
2
votes
1answer
1k views

Connection to localhost dramatically slower than to network server

I have an Excel VBA application that connects to a SQL Server 2008 R2 database through ADODB. When I'm on the network at work, the connection is almost instantaneous. When I am at home working with ...
0
votes
1answer
77 views

Performance tuning in Sybase

Does Sybase have a tool like AWR in Oracle which can be used to identify high load SQL, tell the important waits that are happening, help in understanding the workload? What are the main tools to be ...
3
votes
4answers
6k views

Why is optimistic locking faster than pessimistic locking?

Both forms of locking cause a process to wait for a correct copy of the record if its currently in use by another process. With pessimistic locking, the lock mechanism comes from the DB itself (a ...
0
votes
1answer
44 views

How to define the table structure for measured data in sqlite

I have an embedded system with an sqlite database. How should I define the table structure for the measured data from 4 sensors? Each sensor give us every second an numeric measured value. The ...
0
votes
2answers
63 views

Best database for a real time application [closed]

I am a student doing my Final Year Project where I need to build an android application for on the road navigation. The problem is the application has a feature that alerts the user of nearby incoming ...
0
votes
1answer
89 views

How to prepare executon plan for given sql query on a server with 4 processors (Oracle database)

4 processors means the query runs in parallel. Select /*+ parallel(4) */ T1.A FROM T1,T2,T3 WHERE T1.A = T2.A AND T1.B=T3.B AND T1.C=T3.C Tables T1,T2 and T3 have 4,8, and 16 partitions ...
5
votes
2answers
3k views

Oracle's Merge v. Select->Update/Insert

What is the faster statement? A MERGE or Select->Update/Insert depending on if it returns a value? I'm trying to optimize a database, but I haven't found any speed tests comparing the two. I found ...
1
vote
0answers
82 views

Database performs differently on the two same Xeon E3 1270-v3 Quad Core machines [closed]

Configuration: RAM: 16 GB DDR3. HDD: Seagate 500 GB 7200 3Gb/s 3.5 inch SATA - idential disks. Postgres 9.4, tried with 9.4.1 also Windows 2008 R2 Web Tried these tunings: work_mem = 32MB ...
1
vote
2answers
103 views

Simple query is slow on 4M-rows table

I have in production a MySQL table pageviews with 4M rows that records page views of users on posts. I need to know which posts a specific user have read, but this request takes up to 15 seconds to ...
2
votes
0answers
28 views

Performance of bitwise operators on byte column vs individual bit columns

I'm designing a database schema at the moment, but have a performance query. Our table needs to have (at least) two flags, or boolean values. We can call these IsComplete and IsExportable. The ...
0
votes
2answers
45 views

MySQL Image Queries

I have table employees in MySql database with Id, Name, Gender, HireDate, Photo. Photo field is blob. Now when I run this query: SELECT id FROM employees WHERE Photo IS NULL ; it takes forever to ...
0
votes
2answers
25 views

Can I extrapolate from the progress reporting in MyISAM ALTER?

I'm migrating a 300 million row MyISAM table to add some indexes. Just because it might be relevant, here's my ALTER statement: ALTER TABLE my_table ADD UNIQUE INDEX my_table_abcd (a, b, c, d), ...
0
votes
1answer
61 views

Slow ranking values in MySQL

I have a table of around 30 million retail products, with various INT columns that describe sales counters and pricing at different retailers. I'm supposed to display well over 70 different rankings ...
7
votes
2answers
1k views

Displaying query plans in Server Management Studio

Another SQL server question: I have a simple query that gives me the most CPU intensive SQL since the counters were reset: select top 10 sum(qs.total_worker_time) as total_cpu_time, ...
0
votes
2answers
38 views

Is it a good idea to add a reserved field to a large MySQL table?

As you may know adding a new column to a MySQL table with millions of records is hard and in some cases impossible. Is it a good idea to add a text column to each table (say, meta) to save some ...
3
votes
1answer
138 views

Is a clustered index on a child table in a parent/child relationship the most optimal index?

A clustered index will sort row data in a table according to the ordering of the fields in the index. If so, why would you (or would you not) want to create a clustered index on the child table in a ...