Re: [PATCH] index: add --batch-size=SIZE option

[Eric Wong <e@yhbt.net>]

Eric Wong <e@yhbt.net> wrote:
> On powerful systems, having this option is preferable to
> XAPIAN_FLUSH_THRESHOLD due to lock granularity and contention
> with other processes (-learn, -mda, -watch).
> 
> Setting XAPIAN_FLUSH_THRESHOLD can cause -learn, -mda, and
> -watch to get stuck until an epoch is completely processed.

Fwiw, I've debated with myself on-and-off for a number of years
about adding this knob.

I don't like tuning knobs in general because it's more stuff to
document and support, and more stuff for new users to learn.

However, it's tough to tell how much memory a user is willing to
spend or how long they're willing to wait for -mda/-watch
deliveries while --reindex is happening.  So the default is to
remain conservative and lean towards suboptimal throughput
rather than trigger a swap storm or OOM.