Autarchy of the Private Cave

As described in my previous post, there are some rather simple mechanisms to enable visitor’s browser to cache content, and avoid unnecessary load on your servers. In this post I’ll take a look at some parts of the practical implementation of the caching mechanism on the server, using PHP.
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Sometimes, writing automatic HTML forms processors, you need to post several values with the same name of the form field, e.g.:
collection_gene = str_chrom_name
collection_gene = gene_stable_id

This is against the RFC on form fields design and submitting, but this approach is used – for example, by Ensembl. I spent some time to figure out how to make HTTP_Client and HTTP_Request submit multiple ‘name-value’ pairs instead of one (the latest defined, which overrides the previous). The solution is extremely simple:
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If you fetch large amounts of data (e.g. over 2MB per request) using HTTP_Client (or HTTP_request), you may get “out of memory” fatal errors, especially if:

1. memory_limit is set to default 8M, and
2. you process multiple pages using single non-reset instance of HTTP_Client object.

This problem can manifest itself by producing fatal error after a couple of cycles of successful page retrieval – but always, if run with the same parameters, after some constant or only slightly variable number of cycles.

In my case the problem was that HTTP_Request (a dependancy of HTTP_Client) was holding in memory all the previously fetched pages of the current session (the ‘history’ feature). To force HTTP_Request to hold only the most recent page, you need to ‘disable’ history after creating the HTTP_Client or HTTP_Request object instance:

Hope this helps you.

If you happen to write PHP script, which uses either HTTP_Client or its dependancy HTTP_Request from PEAR, and the script is supposed to work through the HTTP proxy – here are the sample settings you need:

If your proxy does not need authorization – just drop the proxy_user and proxy_pass parameters.