Haha -- I was just about to write PhutilChunkedIterator to try to make the chunking a bit easier, but @vrana already did it. I'll switch to using that. It probably would have made D6789 easier too.

An abstraction which might make this easier is some kind of AutochunkSQLQuery, which might look like this:

$auto_sql = new AutochunkSQLQuery(
  $conn_w,
  'SELECT .. %T .. %Q ... %s ...',
  $table_name,
  AutochunkSQLQuery::BIND,
  $whatever);

Then you just:

$auto_sql->addItem('(%d, %s)', $id, $phid);

When the internal buffer gets big enough, it runs the query. At the end, you:

$auto_sql->flush();

...and it runs a final query with whatever's in its buffer.

Maybe the next time we have one of these that'll be worth writing.