[LUCENE-3584] bulk postings should be codec private

• Type: Task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0-ALPHA
• Lucene Fields: New
• Assignee: Robert Muir
• Reporter: Robert Muir
• Created: 20/Nov/11 16:23
• Updated: 28/Aug/22 13:01
• Resolved: 30/Nov/11 05:19

Description

In LUCENE-2723, a lot of work was done to speed up Lucene's bulk postings read API.

There were some upsides:

• you could specify things like 'i dont care about frequency data up front'.
  This made things like multitermquery->filter and other consumers that don't
  care about freqs faster. But this is unrelated to 'bulkness' and we have a
  separate patch now for this on LUCENE-2929.
• the buffersize for standardcodec was increased to 128, increasing performance
  for TermQueries, but this was unrelated too.

But there were serious downsides/nocommits:

• the API was hairy because it tried to be 'one-size-fits-all'. This made consumer code crazy.
• the API could not really be specialized to your codec: e.g. could never take advantage that e.g. docs and freqs are aligned.
• the API forced codecs to implement delta encoding for things like documents and positions.
  But this is totally up to the codec how it wants to encode! Some codecs might not use delta encoding.
• using such an API for positions was only theoretical, it would have been super complicated and I doubt ever
  performant or maintainable.
• there was a regression with advance(), probably because the api forced you to do both a linear scan thru
  the remaining buffer, then refill...

I think a cleaner approach is to let codecs do whatever they want to implement the DISI
contract. This lets codecs have the freedom to implement whatever compression/buffering they want
for the best performance, and keeps consumers simple. If a codec uses delta encoding, or if it wants
to defer this to the last possible minute or do it at decode time, thats its own business. Maybe a codec
doesn't want to do any buffering at all.