Persistent/keepalive HTTP with the PHP Curl library?

Frank Farmer picture Frank Farmer · Jun 10, 2009 · Viewed 72.4k times · Source

I'm using a simple PHP library to add documents to a SOLR index, via HTTP.

There are 3 servers involved, currently:

  1. The PHP box running the indexing job
  2. A database box holding the data being indexed
  3. The solr box.

At 80 documents/sec (out of 1 million docs), I'm noticing an unusually high interrupt rate on the network interfaces on the PHP and solr boxes (2000/sec; what's more, the graphs are nearly identical -- when the interrupt rate on the PHP box spikes, it also spikes on the Solr box), but much less so on the database box (300/sec). I imagine this is simply because I open and reuse a single connection to the database server, but every single Solr request is currently opening a new HTTP connection via cURL, thanks to the way the Solr client library is written.

So, my question is:

  1. Can cURL be made to open a keepalive session?
  2. What does it take to reuse a connection? -- is it as simple as reusing the cURL handle resource?
  3. Do I need to set any special cURL options? (e.g. force HTTP 1.1?)
  4. Are there any gotchas with cURL keepalive connections? This script runs for hours at a time; will I be able to use a single connection, or will I need to periodically reconnect?

Answer

Piskvor left the building picture Piskvor left the building · Jun 11, 2009

cURL PHP documentation (curl_setopt) says:

CURLOPT_FORBID_REUSE - TRUE to force the connection to explicitly close when it has finished processing, and not be pooled for reuse.

So:

  1. Yes, actually it should re-use connections by default, as long as you re-use the cURL handle.
  2. by default, cURL handles persistent connections by itself; should you need some special headers, check CURLOPT_HTTPHEADER
  3. the server may send a keep-alive timeout (with default Apache install, it is 15 seconds or 100 requests, whichever comes first) - but cURL will just open another connection when that happens.