Validate queue options and exit if option is not acceptable

[silviucpp]

Hello,

Having the following queue:

{ok, Q}= esq:new( "priv/client_producer", [{tts, 0}, {capacity, 0}]).

After I add few items inside the queue and restart the app and do:

esq:head(Q).

I always receive undefined but esq:deq always returns items. I'm expecting head to return same stuff as deq but without removing the item from queue.

I'm using [{tts, 0}, {capacity, 0}] to make sure all items are going on the disk directly. I'm wrong ?

Silviu

[fogfish]

I'll check it... but please keep in mind that tts is queue time-to-sync (rotate) file segments in milliseconds. I would not keep it equal to 0.

[silviucpp]

ohh ok :) thanks

[fogfish]

Right, I've checked your case deeply. Actually, 0 is not valid value for tts and capacity. The capacity defines the size of in-memory queue. The queue would not fetch anything from disk into memory buffer if capacity is 0. You should not afraid to put capacity > 0. The queue always writes data to disk during enqueue.

[fogfish]

I would do the following improvements

• [x] Update README.md. The following statement is not valid: 'Queue starts to "swap" to file segments only when enqueue rate causes an overflow of in-memory buffer.'
• [ ] Accept capacity only if it is > 0
• [ ] Accept tts only if it is > 0

[silviucpp]

@fogfish you can also add documentation for capacity in the readme