Increase buffer sizes in query execution and index scan API

Manik said:

2. Index Key buffering : I was having a chat with John yesterday with regards to bug 13898 and one of the things that we found was the buffer for the entry channel of the indexer connection seems rather small

const _ENTRY_CAP = 1024

func NewIndexConnection(context Context) *IndexConnection {
return &IndexConnection

{ entryChannel: make(EntryChannel, _ENTRY_CAP), stopChannel: make(StopChannel, 1), context: context, }

}

So if and when the indexer will support 30k key scans per second then this entry channel will fill up around 34 milliseconds which is too short a time and maybe causing the I/O timeout errors that we were seeing with bug 13898. My suggestion here would be either increase the size of the buffered entry channel up to a few seconds worth of keys. Perhaps the exact number needs to be tuned and therefore it should be made configurable.

Cheers,
Manik