iilyak commented on code in PR #5558:
URL: https://github.com/apache/couchdb/pull/5558#discussion_r2159296947
##########
src/couch_mrview/src/couch_mrview_index.erl:
##########
@@ -210,7 +215,17 @@ finish_update(State) ->
commit(State) ->
Header = {State#mrst.sig, couch_mrview_util:make_header(State)},
- couch_file:write_header(State#mrst.fd, Header).
+ ok = couch_file:sync(State#mrst.fd),
Review Comment:
Here is the implementation of
`write_header`](https://github.com/apache/couchdb/blob/4adf245b99d5ac2d8ff7f5f49821c4911c6d7688/src/couch/src/couch_file.erl#L435C1-L440C69)
```erlang
write_header(Fd, Data) ->
Bin = ?term_to_bin(Data),
Checksum = generate_checksum(Bin),
% now we assemble the final header binary and write to disk
FinalBin = <<Checksum/binary, Bin/binary>>,
ioq:call(Fd, {write_header, FinalBin}, erlang:get(io_priority)).
```
As you can see the call reaches the `couch_file`'s `gen_server` via `ioq`.
The
[`sync`](https://github.com/apache/couchdb/blob/4adf245b99d5ac2d8ff7f5f49821c4911c6d7688/src/couch/src/couch_file.erl#L301C1-L307C9)
doesn't go via `ioq`
```erlang
sync(Fd) ->
case gen_server:call(Fd, sync, infinity) of
ok ->
ok;
{error, Reason} ->
erlang:error({fsync_error, Reason})
end.
```
Here is what I propose
```erlang
commit_header(Fd, Data) ->
Bin = ?term_to_bin(Data),
Checksum = generate_checksum(Bin),
% now we assemble the final header binary and write to disk
FinalBin = <<Checksum/binary, Bin/binary>>,
ioq:call(Fd, {commit_header, FinalBin}, erlang:get(io_priority)).
...
handle_call({commit_header, _Bin}, From, #file{fd = Fd} = File) ->
sync(Fd),
Result = handle_call({write_header, Bin}, From, File),
sync(Fd),
Result;
```
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