Re: [GSoC] (Is it OK to choose items without % mark in theToDoList) && (is it an acceptable idea to build index on Flash Disk) - Mailing list pgsql-hackers

From Greg Smith
Subject Re: [GSoC] (Is it OK to choose items without % mark in theToDoList) && (is it an acceptable idea to build index on Flash Disk)
Date
Msg-id Pine.GSO.4.64.0803242234240.23484@westnet.com
Whole thread Raw
In response to Re: [GSoC] (Is it OK to choose items without % mark in theToDoList) && (is it an acceptable idea to build index on Flash Disk)  (mx <mx.cogito@gmail.com>)
Responses Re: [GSoC] (Is it OK to choose items without % mark in theToDoList) && (is it an acceptable idea to build index on Flash Disk)
List pgsql-hackers
On Tue, 25 Mar 2008, mx wrote:

> The atom unit of flash is page(512~2048byte typically). Page are 
> organized into blocks, typically of 32 or 64 pages. All read write and 
> write operations happen at page granularity, but erase operations happen 
> at block granularity.

You made a subtle switch here I wanted to emphasise.  Your original 
message suggested flash is an increasingly important storage mechanism 
because flash devices like SSD drives are going to be more popular in the 
future; that is true.  However, what you're describing is something more 
like how flash is used in raw embedded systems applications.  The kinds of 
SSD drives that are becoming popular for database use abstract away all of 
this low-level block mess and hide it with approaches like sophisticated 
write-leveling algorithms.  You don't (and possibly can't) even know what 
the underlying structure is like.  And even if you did, the fact that 
there's a always a regular operating system and filesystem underneath 
PostgreSQL writes will make it undertain the writes are only touching the 
tiny portion of flash you want to target anyway.  They may write a whole 
OS block regardless.

Accordingly, it's my opinion that while this topic is interesting and a 
good one for your thesis, this particular project would not be too 
valuable to the typical PostgreSQL user whether or not SSD becomes 
popular.  Working to optimize raw flash writes is really more of an 
operating system level project than a database one.  I also have my doubts 
about whether you could get this done within the GSoC timeframe; better to 
pick a less ambitious goal than rewriting the whole storage manager 
interface I would think.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD


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