expand readme to include more hints

README.textile

@@ -17,17 +17,40 @@ h2. Setup
 The library evolves around a delayed_jobs table which looks as follows: 
 
   create_table :delayed_jobs, :force => true do |table|
-    table.integer  :priority, :default => 0
-    table.integer  :attempts, :default => 0
-    table.text     :handler
-    table.string   :last_error
-    table.datetime :run_at
-    table.datetime :locked_at
-    table.datetime :failed_at
-    table.string   :locked_by
+    table.integer  :priority, :default => 0      # Allows some jobs to jump to the front of the queue
+    table.integer  :attempts, :default => 0      # Provides for retries, but still fail eventually.
+    table.text     :handler                      # YAML-encoded string of the object that will do work
+    table.string   :last_error                   # reason for last failure (See Note below)
+    table.datetime :run_at                       # When to run. Could be Time.now for immediately, or sometime in the future.
+    table.datetime :locked_at                    # Set when a client is working on this object
+    table.datetime :failed_at                    # Set when all retries have failed (actually, by default, the record is deleted instead)
+    table.string   :locked_by                    # Who is working on this object (if locked)
     table.timestamps
   end
-
+
+On failure, the job is scheduled again in 5 seconds + N ** 4, where N is the number of retries.
+
+The default MAX_ATTEMPTS is 25. After this, the job either deleted (default), or left in the database with "failed_at" set.
+With the default of 25 attempts, the last retry will be 20 days later, with the last interval being almost 100 hours.
+
+The default MAX_RUN_TIME is 4.hours. If your job takes longer than that, another computer could pick it up. It's up to you to
+make sure your job doesn't exceed this time. You should set this to the longest time you think the job could take.
+
+By default, it will delete failed jobs (and it always deletes successful jobs). If you want to keep failed jobs, set
+Delayed::Job.destroy_failed_jobs = false. The failed jobs will be marked with non-null failed_at.
+
+Here is an example of changing job parameters in Rails:
+
+  # config/initializers/delayed_job_config.rb
+  Delayed::Job.destroy_failed_jobs = false
+  silence_warnings do
+    Delayed::Job.const_set("MAX_ATTEMPTS", 3)
+    Delayed::Job.const_set("MAX_RUN_TIME", 5.minutes)
+  end
+
+Note: If your error messages are long, consider changing last_error field to a :text instead of a :string (255 character limit).
+
+
 h2. Usage
 
 Jobs are simple ruby objects with a method called perform. Any object which responds to perform can be stuffed into the jobs table.
@@ -64,6 +87,12 @@ You can also run by writing a simple @script/job_runner@, and invoking it extern
   Delayed::Worker.new.start  
 </code></pre>
 
+Workers can be running on any computer, as long as they have access to the database and their clock is in sync. You can even
+run multiple workers on per computer, but you must give each one a unique name. (TODO: put in an example)
+Keep in mind that each worker will check the database at least every 5 seconds.
+
+Note: The rake task will exit if the database has any network connectivity problems.
+
 h3. Cleaning up
 
 You can invoke @rake jobs:clear@ to delete all jobs in the queue.