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    <p>The most simple way to solve this is to use an OS which solves that for you under the hood, like Linux. Give it enough RAM to hold 10% of the objects in RAM and it will try to keep as many of them in the cache as possible reducing the load time to 0. The recent <em>server</em> versions of Windows might work, too (some of them didn't for me, that's why I'm mentioning this).</p> <p>If this is a no go, try this algorithm:</p> <ul> <li><p>Create a very big file on the harddisk. It is very important that you write this in one go so the OS will allocate a continuous space on disk.</p></li> <li><p>Write all your objects into that file. Make sure that each object is the same size (or give each the same space in the file and note the length in the first few bytes of of each chunk). Use an empty harddisk or a disk which has just been defragmented.</p></li> <li><p>In a data structure, keep the offsets of each data chunk and how often it is accessed. When it is accessed very often, swap its position in the file with a chunk that is closer to the start of the file and which has a lesser access count.</p></li> <li><p>[EDIT] Access this file with the memory-mapped API of your OS to allow the OS to effectively cache the most used parts to get best performance until you can optimize the file layout next time.</p></li> </ul> <p>Over time, heavily accessed chunks will bubble to the top. Note that you can collect the access patterns over some time, analyze them and do the reorder over night when there is little load on your machine. Or you can do the reorder on a completely different machine and swap the file (and the offset table) when that's done.</p> <p>That said, you should really rely on a modern OS where a lot of clever people have thought long and hard to solve these issues for you.</p>
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