googlebot, msn adding 100s of MBs to cache_amazon_store

I started getting 'disk full' warnings due to huge growth in the size of my drupal DB, mainly due to amazing bloat in the tables cache_amazon_store and cache_amazon_store_searches. Watchdog dblog is lousy with lengthy warnings like the one below. There are so many of these, my DB grows by hundreds of MB in size. I've 'controlled' that (at least temporarily) by reducing the cache times drastically and renaming the URL (from amazon_store to something else, to lose the bots, at least for a while).

To me, it looks like it starts this way. The bot visits a single amazon item, like:

http://mywebsite.com/amazon_store/item/0060930349

Then, the bot follows the Author link to reach:

http://mywebsite.com/amazon_store?Author=Paul%20Johnson&SearchIndex=Books

and by following the pager links, the bot gets to a

http://mywebsite.com/amazon_store?page=2&Author=Paul%20Johnson&SearchInd...

Looks to me like those dang bots end up indexing a large fraction of Amazon.com (with my site as a kind of proxy). Which is fine, except my DB can't handle all those entries.

But here's the real reason I'm reporting. Take a look at that dblog entry below and you'll see "page=982490" in the URL!! Such a large page number throws the error, but I can't fathom how the bot gets that far. I thought maybe the 'last' link in the pager, but so far I can't reproduce getting such a large page number.

Looking through other issues I've seen discussions of caching issues and possible use of 'nofollow' tag to discourage bots. But I've not seen anyone report this sort of cache bloat, and the error associated with giant, mysterious page numbers. So, I thought I'd report this mainly to see if anyone else has seen similar, or has suggestions on how to avoid.

Thanks for all the hard work! Any suggestions appreciated.

-- Cronin

Details
Type	amazon
Date	Friday, July 6, 2012 - 11:32
User	Anonymous (not verified)
Location	http://cvining.com/amazon_store?page=982490&author=Sarah%20Vowell
Referrer	
Message	There was an error accessing amazon. Message=Amazon error returned. Code=AWS.ParameterOutOfRange}, Message=The value you specified for ItemPage is invalid. Valid values must be between 1 and 10. 
//, results=SimpleXMLElement Object ( [OperationRequest] => SimpleXMLElement Object ( [HTTPHeaders] => SimpleXMLElement Object ( [Header] => SimpleXMLElement Object ( [@attributes] => Array ( [Name] => UserAgent [Value] => Drupal (+http://drupal.org/) ) ) )

[Message snipped for brevity]
Severity	notice
Hostname	66.249.71.219
Operations