[couchdb] branch optimise-view-read created (now d9b20d5)

[ga...@apache.org]

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garren pushed a change to branch optimise-view-read
in repository https://gitbox.apache.org/repos/asf/couchdb.git.


      at d9b20d5  Optimize view read latency when the view ready

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     new d9b20d5  Optimize view read latency when the view ready

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[couchdb] 01/01: Optimize view read latency when the view ready

[ga...@apache.org]

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

garren pushed a commit to branch optimise-view-read
in repository https://gitbox.apache.org/repos/asf/couchdb.git

commit d9b20d5992e9f2d3f68187c271abe57cae7d79fe
Author: Garren Smith <ga...@gmail.com>
AuthorDate: Tue Nov 26 16:27:50 2019 +0200

    Optimize view read latency when the view ready
    
    If the view is already built, read the view status and view
    in the same transaction. This will improve view read latency.
---
 src/couch_views/src/couch_views.erl | 46 +++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 20 deletions(-)

diff --git a/src/couch_views/src/couch_views.erl b/src/couch_views/src/couch_views.erl
index 7c7588c..322415b 100644
--- a/src/couch_views/src/couch_views.erl
+++ b/src/couch_views/src/couch_views.erl
@@ -44,36 +44,42 @@ query(Db, DDoc, ViewName, Callback, Acc0, Args0) ->
         false -> ok
     end,
 
-    ok = maybe_update_view(Db, Mrst, Args3),
-
     try
-        couch_views_reader:read(Db, Mrst, ViewName, Callback, Acc0, Args3)
-    after
-        UpdateAfter = Args3#mrargs.update == lazy,
-        if UpdateAfter == false -> ok; true ->
-            couch_views_jobs:build_view_async(Db, Mrst)
-        end
+        fabric2_fdb:transactional(Db, fun(TxDb) ->
+            ok = maybe_update_view(TxDb, Mrst, Args3),
+            read_view(TxDb, Mrst, ViewName, Callback, Acc0, Args3)
+        end)
+    catch throw:{build_view, WaitSeq} ->
+        couch_views_jobs:build_view(Db, Mrst, WaitSeq),
+        read_view(Db, Mrst, ViewName, Callback, Acc0, Args3)
     end.
 
 
+read_view(Db, Mrst, ViewName, Callback, Acc0, Args) ->
+    fabric2_fdb:transactional(Db, fun(TxDb) ->
+        try
+            couch_views_reader:read(TxDb, Mrst, ViewName, Callback, Acc0, Args)
+        after
+            UpdateAfter = Args#mrargs.update == lazy,
+            if UpdateAfter == false -> ok; true ->
+                couch_views_jobs:build_view_async(TxDb, Mrst)
+            end
+        end
+    end).
+
+
 maybe_update_view(_Db, _Mrst, #mrargs{update = false}) ->
     ok;
 
 maybe_update_view(_Db, _Mrst, #mrargs{update = lazy}) ->
     ok;
 
-maybe_update_view(Db, Mrst, _Args) ->
-    WaitSeq = fabric2_fdb:transactional(Db, fun(TxDb) ->
-        DbSeq = fabric2_db:get_update_seq(TxDb),
-        ViewSeq = couch_views_fdb:get_update_seq(TxDb, Mrst),
-        case DbSeq == ViewSeq of
-            true -> ready;
-            false -> DbSeq
-        end
-    end),
-
-    if WaitSeq == ready -> ok; true ->
-        couch_views_jobs:build_view(Db, Mrst, WaitSeq)
+maybe_update_view(TxDb, Mrst, _Args) ->
+    DbSeq = fabric2_db:get_update_seq(TxDb),
+    ViewSeq = couch_views_fdb:get_update_seq(TxDb, Mrst),
+    case DbSeq == ViewSeq of
+        true -> ok;
+        false -> throw({build_view, DbSeq})
     end.