optimization

MySQL Query performance - huge difference in time

I have a query that is returning in vastly different amounts of time between 2 datasets. For one set (database A) it returns in a few seconds, for the other (database B)....well I haven't waited long enough yet, but over 10 minutes. I have dumped both of these databases to my local machine where I can reproduce the issue running MySQL 5....

Overhead of calling tiny functions from a tight inner loop? [C++]

Say you see a loop like this one: for(int i=0; i<thing.getParent().getObjectModel().getElements(SOME_TYPE).count(); ++i) { thing.getData().insert( thing.GetData().Count(), thing.getParent().getObjectModel().getElements(SOME_TYPE)[i].getName() ); } if this was Java I'd probably not think twice. But in performance-...

How can i benchmark method execution time in java?

I have a program which i have myself written in java, but I want to test method execution times and get timings for specific methods. I was wondering if this is possible, by maybe somehow an eclipse plug-in? or maybe inserting some code? I see, it is quite a small program, nothing more than 1500 lines, which would be better a dedicated ...

C# Improvement on a Fire-and-Forget

Greetings I have a program that creates multiples instances of a class, runs the same long-running Update method on all instances and waits for completion. I'm following Kev's approach from this question of adding the Update to ThreadPool.QueueUserWorkItem. In the main prog., I'm sleeping for a few minutes and checking a Boolean in th...

Optimizing PHP require_once's for low disk i/o?

Q1) I'm designing a CMS (-who isn't!) but priority is being given to caching. Literally everything is cached. DB rows, DB id queries, Configuration data, processed data, compiled templates. Currently it has two layers of caching. The first is a opcode cache or memory cache such as apc, eaccelerator, xcache or memcached. If an entry is ...

C++ Performance/memory optimization guidelines

Hi All, Does anyone have a resource for C++ memory optimization guidelines? Best practices, tuning, etc? As an example: Class xxx { public: xxx(); virtual ~xxx(); protected: private: }; Would there be ANY benefit on the compiler or memory allocation to get rid of protected and private since there the...

exchanging 2 memory positions

I am working with OpenCV and Qt, Opencv use BGR while Qt uses RGB , so I have to swap those 2 bytes for very big images. There is a better way of doing the following? I can not think of anything faster but looks so simple and lame... int width = iplImage->width; int height = iplImage->height; uchar *iplImagePtr = (uchar *) iplIm...

SQL-query task, decision?

There is a table of currencies rates in MS SQL Server 2005: ID | CURR | RATE | DATE 1   | USD   | 30      | 01.10.2010 3   | GBP   | 45      | 07.10.2010 5   | USD   | 31      | 08.10.2010 7   | GBP   | 46      | 09.10.2010 9   | USD   | 32      | 12.10.2010 11 | GBP   | 48      | 03.10.2010 Rate are updated in real time and there are ...

What approach to take for SIMD optimizations

Hi, I am trying to optimize below code for SIMD operations (8way/4way/2way SIMD whiechever possible and if it gives gains in performance) I am tryin to analyze it first on paper to understand the algorithm used. How can i optimize it for SIMD:- void idct(uint8_t *dst, int stride, int16_t *input, int type) { int16_t *ip = input...

optimizing oracle query

I'm having a hard time wrapping my head around this query. it is taking almost 200+ seconds to execute. I've pasted the execution plan as well. SELECT user_id , ROLE_ID , effective_from_date , effective_to_date , participant_code , ACTIVE FROM CMP_USER_ROLE E ...

I'm doing a lot of lists and dictionary sorting...and this is causing memory errors in Python website.

I retrieved data from the log table in my database. Then I started finding unique users, comparing/sorting lists, etc. In the end I got down to this. stats = {'2010-03-19': {'date': '2010-03-19', 'unique_users': 312, 'queries': 1465}, '2010-03-18': {'date': '2010-03-18', 'unique_users': 329, 'queries': 1659}, '2010-03-17': {'date': '20...

MySQL won't use index for query?

I have this table: CREATE TABLE `point` ( `id` INT(11) NOT NULL AUTO_INCREMENT, `siteid` INT(11) NOT NULL, ...

How to speed-up a simple method (preferably without changing interfaces or data structures)?

I have some data structures: all_unordered_m is a big vector containing all the strings I need (all different) ordered_m is a small vector containing the indexes of a subset of the strings (all different) in the former vector position_m maps the indexes of objects from the first vector to their position in the second one. The string...

SQLite3-ruby extremely slow under 1.9.1?

I decided to upgrade my server to Ruby 1.9.1, and a lot of things are indeed much faster. However, I have a process that dumps a database to sqlite, and it's become glacially slow. What used to take 30 seconds now takes upwards of 10 minutes. The code does several create table statements, and then lots of inserts. The insert statements ...

text indexes vs integer indexes in mysql

Hey, I have always tried to have an integer primary key on a table no matter what. But now I am questioning if this is always necessary. Let's say I have a product table and each product has a globally unique SKU number - that would be a string of say 8-16 characters. Why not make this the PK? Typically I would make this field a uni...

Which way to store this data is effective?

I am writing a game, which need a map, and I want to store the map. The first thing I can think of, is using a 2D-array. But the problem is what data should I store in the 2D-array. The player can tap different place to have different reaction. So, I am thinking store a 2D-array with objects, when player click some position, and I find i...

Question about Cost in Oracle Explain Plan

When Oracle is estimating the 'Cost' for certain queries, does it actually look at the amount of data (rows) in a table? For example: If I'm doing a full table scan of employees for name='Bob', does it estimate the cost by counting the amount of existing rows, or is it always a set cost? ...

Improving the speed of php

I'm currently working on a website in PHP, and I'm wondering what the best practices/methods are to reduce the time requests take. I've build the site in a modular way, so a page would consist of a number of modules, and each of these would need to request information. For example, I have a cart module, that (if a cart is set) will fetc...

Optimizing Python code with many attribute and dictionary lookups

I have written a program in Python which spends a large amount of time looking up attributes of objects and values from dictionary keys. I would like to know if there's any way I can optimize these lookup times, potentially with a C extension, to reduce the time of execution, or if I need to simply re-implement the program in a compiled ...

Does a c/c++ compiler optimize constant divisions by power-of-two value into shifts?

Question says it all. Does anyone know if the following... size_t div(size_t value) { const size_t x = 64; return value / x; } ...is optimized into? size_t div(size_t value) { return value >> 6; } Do compilers do this? (My interest lies in GCC). Are there situations where it does and others where it doesn't? I would re...