[mabbo]

Simplest way? grep.

You've got one entity to search per line, let's presume (if not, pre-process once to a new big file so that you do).

You want to find all entities that have propertyName = "Foo". So run "grep 'Foo' file" and put the result into your actual parsing/processing. You just removed some percentage of your data before the difficult parsing even began. Need to search on multiple fields?

  cat input | grep 'Foo' | grep 'Bar' | actualProcessing