[couchdb] branch shard-split updated: Add calculate_max_n to mem3_util module

[va...@apache.org]

This is an automated email from the ASF dual-hosted git repository.

vatamane pushed a commit to branch shard-split
in repository https://gitbox.apache.org/repos/asf/couchdb.git


The following commit(s) were added to refs/heads/shard-split by this push:
     new e9b94c8  Add calculate_max_n to mem3_util module
e9b94c8 is described below

commit e9b94c894e89fdd8a8b74b90a9c3cda50cdb0c77
Author: Nick Vatamaniuc <va...@apache.org>
AuthorDate: Tue Feb 26 17:59:32 2019 -0500

    Add calculate_max_n to mem3_util module
    
    This can be used to calculate the maximum N (number of copies) for a
    given set of shards.
---
 src/mem3/src/mem3_util.erl | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/mem3/src/mem3_util.erl b/src/mem3/src/mem3_util.erl
index e81ceb2..e8cba5d 100644
--- a/src/mem3/src/mem3_util.erl
+++ b/src/mem3/src/mem3_util.erl
@@ -27,7 +27,8 @@
     get_ring/3,
     get_ring/4,
     non_overlapping_shards/1,
-    non_overlapping_shards/3
+    non_overlapping_shards/3,
+    calculate_max_n/1
 ]).
 
 %% do not use outside mem3.
@@ -409,6 +410,25 @@ non_overlapping_shards(Shards, Start, End) ->
     end, Shards).
 
 
+% Given a list of shards, return the maximum number of copies
+% across all the ranges. If the ring is incomplete it will return 0.
+% If there it is an n = 1 database, it should return 1, etc.
+calculate_max_n(Shards) ->
+    Ranges = lists:map(fun(Shard) ->
+        [B, E] = mem3:range(Shard),
+        {B, E}
+    end, Shards),
+    calculate_max_n(Ranges, get_ring(Ranges), 0).
+
+
+calculate_max_n(_Ranges, [], N) ->
+    N;
+
+calculate_max_n(Ranges, Ring, N) ->
+    NewRanges = Ranges -- Ring,
+    calculate_max_n(NewRanges, get_ring(NewRanges), N + 1).
+
+
 get_ring(Ranges) ->
     get_ring(Ranges, fun sort_ranges_fun/2, 0, ?RING_END).
 
@@ -530,6 +550,18 @@ non_overlapping_shards_test() ->
     ]].
 
 
+calculate_max_n_test_() ->
+     [?_assertEqual(Res, calculate_max_n(Shards)) || {Res, Shards} <- [
+        {0, []},
+        {0, [shard(1, ?RING_END)]},
+        {1, [shard(0, ?RING_END)]},
+        {1, [shard(0, ?RING_END), shard(1, ?RING_END)]},
+        {2, [shard(0, ?RING_END), shard(0, ?RING_END)]},
+        {2, [shard(0, 1), shard(2, ?RING_END), shard(0, ?RING_END)]},
+        {0, [shard(0, 3), shard(5, ?RING_END), shard(1, ?RING_END)]}
+     ]].
+
+
 shard(Begin, End) ->
     #shard{range = [Begin, End]}.