Optimizing database to avoid hitting memory limits?

I'm using version 1.5.1. When I login to admin and try to go to Categories/Products, I get either a 500 internal server error or it just sits and sits and never loads. Dreamhost says I'm hitting my memory limit. Coincidentally (or not) they moved me to a new server yesterday and the problem started then. They've basically refused to help me in any way. I don't know where to start other than trying to optimize my database and I can't find any instructions on how to accomplish that. I'm at the end of my rope with these problems and I don't know what else to do. I can't access my catalog until I get this fixed. Could someone please help me.

PHP memory limits are not related to database optimization.

Your PHP memory limit is the amount of RAM allocated by the server's administrator to any PHP script.

Chances are that the new server they put you on has less RAM available to PHP because they've either not tuned it to use more than the (very low) defaults set up by a new(or upgraded) PHP installation, or they're intentionally limiting users on your particular hosting plan. Either way they should increase the limit to something reasonable. Especially when, as you say, the problem did not exist before they moved you to a different server.

Thanks for the reply, Dr. Byte. I'm on yet another live chat with them and I think the guy who is helping me understands my problem and is helping. :) Should be fixed finally here in a few minutes. Thanks!

Dream Hosts should really change their name to Nightmare Hosts. I have found them to be totally useless for eCommerce hosting.

DrByte:

PHP memory limits are not related to database optimization.

Your PHP memory limit is the amount of RAM allocated by the server's administrator to any PHP script.

Chances are that the new server they put you on has less RAM available to PHP because they've either not tuned it to use more than the (very low) defaults set up by a new(or upgraded) PHP installation, or they're intentionally limiting users on your particular hosting plan. Either way they should increase the limit to something reasonable. Especially when, as you say, the problem did not exist before they moved you to a different server.

Dr. Byte - what would be a reasonable memory limit in your opinion? I checked my stats and it's showing I'm using 397mb of cached memory and 472mb of actual memory for a total of 869mb. Is that normal?

I'm not sure what you're looking at to get those numbers.

But a PHP memory_limit setting of 256M should be very reasonable.