[couchdb-erlfdb] 02/02: Do not commit read-only transactions

[va...@apache.org]

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

commit 01f79dbb3938ceac4638752953b84a396d78c0ce
Author: Nick Vatamaniuc <va...@apache.org>
AuthorDate: Wed Apr 22 12:25:31 2020 -0400

    Do not commit read-only transactions
    
    This might save a round-trip to the network thread [1]. It also follows the
    recommendation in the C api docs [2].
    
    [1] https://forums.foundationdb.org/t/performance-of-read-only-transactions/1998
    [2] https://apple.github.io/foundationdb/api-c.html#c.fdb_transaction_commit
    
    However, it turns out in order for the watches to fire the read-only
    transaction still has to commit, so avoid this optimization if has_watches(Tx)
    is true.
---
 src/erlfdb.erl | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/erlfdb.erl b/src/erlfdb.erl
index 2b62b91..b50f843 100644
--- a/src/erlfdb.erl
+++ b/src/erlfdb.erl
@@ -653,7 +653,10 @@ clear_erlfdb_error() ->
 do_transaction(?IS_TX = Tx, UserFun) ->
     try
         Ret = UserFun(Tx),
-        wait(commit(Tx)),
+        case is_read_only(Tx) andalso not has_watches(Tx) of
+            true -> ok;
+            false -> wait(commit(Tx))
+        end,
         Ret
     catch error:{erlfdb_error, Code} ->
         put(?ERLFDB_ERROR, Code),