Add a new "list_parallelism" advanced option (requires use_arrow_list) which
splits a directory's blob-name keyspace into ranges and lists them
concurrently using the Arrow startFrom/endBefore range parameters. Both
recursive (ListR) and single-directory listings benefit.
The keyspace is sharded with a single-case (digit+lowercase) character
ladder. Single case is deliberate: the service validates startFrom /
endBefore case-insensitively (while listing case-sensitively), so a
mixed-case boundary pair is rejected with a 400; its endBefore filtering is
byte-ordered, so the listing is exact.
The service only honours endBefore on the Arrow listing path of accounts with
Blob Listing with Apache Arrow enabled: elsewhere it either rejects the
request with 400 OperationNotSupportedWithFeatureMissing or, if it fell back
to XML, would ignore the shards' upper bounds. Both cases are detected and
the parallel listing falls back to a sequential listing.
Listing 100,000 objects from a well-connected server:
config time vs XML
xml 23.9s 1.0x
use_arrow_list 6.9s 3.5x
list_parallelism=2 4.4s 5.5x
list_parallelism=4 2.8s 8.4x
list_parallelism=6 2.2s 10.9x
list_parallelism=10 1.5s 15.4x
list_parallelism=20 1.4s 17.6x
list_parallelism=30 1.1s 21.7x
So Apache Arrow listing alone is ~3.5x faster than XML, and parallel listing
takes that to ~20x. The ladder caps at 37 shards, so the benefit plateaus
beyond list_parallelism=30.
The option is hidden from the configurator, command line help and docs
until the feature is officially released.
Nick Craig-Wood
d183f4a43d