[GitHub] [couchdb] nickva commented on a change in pull request #2707: Set DbPrefix with value allocated by erlfdb_hca

[GitBox <gi...@apache.org>]

nickva commented on a change in pull request #2707: Set DbPrefix with value allocated by erlfdb_hca
URL: https://github.com/apache/couchdb/pull/2707#discussion_r396566069
 
 

 ##########
 File path: src/fabric/src/fabric2_fdb.erl
 ##########
 @@ -177,10 +177,13 @@ create(#{} = Db0, Options) ->
         layer_prefix := LayerPrefix
     } = Db = ensure_current(Db0, false),
 
-    % Eventually DbPrefix will be HCA allocated. For now
-    % we're just using the DbName so that debugging is easier.
     DbKey = erlfdb_tuple:pack({?ALL_DBS, DbName}, LayerPrefix),
-    DbPrefix = erlfdb_tuple:pack({?DBS, DbName}, LayerPrefix),
+    DefDbPref = ?DEFAULT_DB_PREFIX,
+    AllDbPrefix = erlfdb_util:get(Options, db_prefix, DefDbPref),
+    DbId = erlfdb_tuple:pack({AllDbPrefix}, AllDbPrefix),
+    DbPrefixAllocator = erlfdb_hca:create(erlfdb_tuple:pack({DbId}, <<"hca">>)),
+    AllocPrefix = erlfdb_hca:allocate(DbPrefixAllocator, Tx),
+    DbPrefix = erlfdb_tuple:pack({?DBS, AllocPrefix}, LayerPrefix),
 
 Review comment:
   I wonder we could just keep the HCA counters right under the the `LayerPrefix?
   
   As in:
   
   ```
   DbPrefixAlloc = erlfdb_hca:create(erlfdb_tuple:pack({?DB_HCA}, LayerPrefix))
   ```
   
   And then define `DB_HCA` to be in fabric2.hrl alongside `ALL_DBS`. 
   
   ```
   ...
   -define(ALL_DBS, 1).
   -define(DB_HCA, 2).
   ```
   
   Then we don't even need the `DEFAULT_DB_PREFIX` since we'd always be creating these instances under `LayerPrefix` as well. In other words, they won't clash with FDB directory nodes.
   
   Would that work? 

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