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  • B-trees, databases, sequential inputs, and speed.

    - by IanC
    I know from experience that b-trees have awful performance when data is added to them sequentially (regardless of the direction). However, when data is added randomly, best performance is obtained. This is easy to demonstrate with the likes of an RB-Tree. Sequential writes cause a maximum number of tree balances to be performed. I know very few databases use binary trees, but rather used n-order balanced trees. I logically assume they suffer a similar fate to binary trees when it comes to sequential inputs. This sparked my curiosity. If this is so, then one could deduce that writing sequential IDs (such as in IDENTITY(1,1)) would cause multiple re-balances of the tree to occur. I have seen many posts argue against GUIDs as "these will cause random writes". I never use GUIDs, but it struck me that this "bad" point was in fact a good point. So I decided to test it. Here is my code: SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[T1]( [ID] [int] NOT NULL CONSTRAINT [T1_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO CREATE TABLE [dbo].[T2]( [ID] [uniqueidentifier] NOT NULL CONSTRAINT [T2_1] PRIMARY KEY CLUSTERED ([ID] ASC) ) GO declare @i int, @t1 datetime, @t2 datetime, @t3 datetime, @c char(300) set @t1 = GETDATE() set @i = 1 while @i < 2000 begin insert into T2 values (NEWID(), @c) set @i = @i + 1 end set @t2 = GETDATE() WAITFOR delay '0:0:10' set @t3 = GETDATE() set @i = 1 while @i < 2000 begin insert into T1 values (@i, @c) set @i = @i + 1 end select DATEDIFF(ms, @t1, @t2) AS [Int], DATEDIFF(ms, @t3, getdate()) AS [GUID] drop table T1 drop table T2 Note that I am not subtracting any time for the creation of the GUID nor for the considerably extra size of the row. The results on my machine were as follows: Int: 17,340 ms GUID: 6,746 ms This means that in this test, random inserts of 16 bytes was almost 3 times faster than sequential inserts of 4 bytes. Would anyone like to comment on this? Ps. I get that this isn't a question. It's an invite to discussion, and that is relevant to learning optimum programming.

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  • How to tell svn to not manage history for one file

    - by Prabu
    I don't know whether SVN has this feature, How do I tell svn to not maintain the history of changes for a file but it should have only the latest version of the file. Of course this is not the work of a version control, but it will be useful if I want to have some binary files within the repo without versioning.

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  • PHP Upload file enhance security

    - by mandril
    Hey.. my question is how to prevent someone upload a virus or some malicious code with the extension you pretend for example i have a pdf file uploader, anyone can upload a binary with pdf camouflage there are lots of programs to do that.

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  • Python's cPickle deserialization from PHP?

    - by Ciantic
    Hi! I have to deserialize a dictionary in PHP that was serialized using cPickle in Python. In this specific case I probably could just regexp the wanted information, but is there a better way? Any extensions for PHP that would allow me to deserialize more natively the whole dictionary? Apparently it is serialized in Python like this: import cPickle as pickle data = { 'user_id' : 5 } pickled = pickle.dumps(data) print pickled Contents of such serialization cannot be pasted easily to here, because it contains binary data.

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  • How do Hex editors display data so quickly?

    - by user146780
    I'v created a Notepad-like application and if I load a 1MB file into the textbox, it takes about 1 minute. The Visual Studio Binary editor displays lines, Hex, and ascii versions in a fraction of a second. How do they get the data into the textbox so quickly? Thanks

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  • Boost Serialization Library upgrade

    - by Konstantin
    Hello! How do I know that I can safely upgrade Boost Serialization Library on a production system without breaking compatibility with the existing data ? Is there any test that I should perform in order to be sure that all data stored in the binary format by previous version of the library will be successfully read by the new one ? Does Boost Serialization library itself guarantee some sort of compatibility between versions ?

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  • GDB disas question about address values

    - by user324994
    I'm working with a binary file that I disas'd in gdb. Right now I'm just examining the return value of a function. 0x08048604 <playGame+78>: ret Is the address shown the address where ret is stored in the function? Or is it just the address of the instruction to return the ret value?

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  • ASP.NET MVC image upload store location (db vs filesystem)

    - by adrin
    I am writing web application using ASP.NET MVC + NHibernate + Postres stack. I wonder if images uploaded should be stored in database as binary blobs or on filesystem (and reference only in db). One advantage of db storage I can think of is easy backup/recovery of all data without reverting to filesystem copy tools. On the other hand I suspect that filesystem access may be faster (but is it especially when dealing with many concurrent requests?) What are your suggestions?

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  • Hash Table v/s STL map in C++

    - by anon
    Hi, I am trying to learn C++ maps. Was just wondering about the implementation of STL map. I read it employs Binary search tree. Is there a implementation of hash table in STL? How exactly do STL map stores Key Value pairs?

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