doc: backend protocol, wanted features

closes #478

README.md

@@ -323,6 +323,8 @@ For more information see the [the PgJDBC driver documentation](http://jdbc.postg
 
 PgJDBC development is carried out on the [PgJDBC mailing list](https://jdbc.postgresql.org/community/mailinglist.html) and on [GitHub](https://github.com/pgjdbc/pgjdbc).
 
+Set of "backend protocol missing features" is collected in [backend_protocol_v4_wanted_features.md](backend_protocol_v4_wanted_features.md)
+
 ### Bug reports
 
 For bug reports please post on pgsql-jdbc or add a GitHub issue. If you include

backend_protocol_v4_wanted_features.md

@@ -0,0 +1,80 @@
+# PostgreSQL backend protocol: wanted features
+
+Current protocol is documented here: http://www.postgresql.org/docs/9.4/static/protocol.html
+
+It turns out it lacks certain features, thus it makes clients more complex, slower, etc.
+
+Here's the list of features that often appear in discussions.
+
+## Features
+
+### Binary transfer vs exact data type
+
+Current protocol supports text and binary transfer.
+It turns out in text mode backend does not need to know the exact data type. In most cases it can
+easily deduce the data type. Binary mode is typically faster, however when consuming binary,
+backend assumes the data type is exact and it does not consider casts.
+
+It would be nice to have an ability to pass a value in binary form (for efficiency) yet
+make backend deduce proper data type for it.
+
+
+Kevin Wooten: my biggest request is always to treat binary types as if the client “just knows” how
+to handle them. There are numerous cases with the text format where the server will coerce columns
+to the most correct type and it will not do this for binary requests; it just spits out a complaint
+that you’ve got the wrong type.
+
+That, and being able to switch to “prefer binary” mode in the protocol. So when I make an non-bound
+request I can get the results back in binary. Currently you can only get them in text format.
+This has a couple of implications. First, speed, you always have to bind before querying to get
+binary results. Second is multiple SQL statements in a single request, which you
+cannot do in bound requests.
+
+### Non-trivial semantics of numerics in text mode
+
+In text mode, numerics and money types are transferred with unknown decimal separator.
+This makes it hard to decode the value as it is locale-dependent.
+
+See: https://github.com/pgjdbc/pgjdbc/pull/439
+
+### Lack of `prepared statement invalidated` messages from backend
+
+Server-prepared statement might become invalid due to table structure change, column type change,
+etc.
+It results in "your prepared statement is no longer valid". This is no fun.
+
+See: https://github.com/pgjdbc/pgjdbc/pull/451
+
+## Brain dumps
+
+### Álvaro Hernández
+
+- Uniform headers (type byte). Some messages (startup, ssl, etc) don't have the type byte marker.
+This is annoying.
+- Byte type re-use. The type byte is re-used across senders and receivers. It is unambiguous,
+but it is still very weird.
+- Query pipelining. There has been much discussion about it. I don't have a clear conclusion other
+than it's somehow possible, but requires driver support (keep track of sent/received messages
+and errors). This could be easily handled with protocol support, like using a unique id for every
+message and including in the reply that id.
+- Cluster support. Real production environments are clusters (sets of PostgreSQL servers
+using any kind of replication). Protocol should be concerned with this, specially if some HA
+mechanisms are built into the protocol.
+- Server metadata without authentication. Some messages should be able to be exchanged
+to get information about servers (like version, read/write state and probably others) without
+having to authenticate and involve in lengthy processes.
+- No out-of-band messages (like query cancellation)
+- Simplified design (current is too complex and with too many messages)
+- Specified in a formal syntax (I mean not English, a formal language for specifying it) and
+with a TCK (Test Compatibility Kit)
+- Allow some controlled form of protocol extensibility
+- A back-pressure method for query results
+- All the "usual suspects": support for binary format, partial query results,
+large objects and so on
+
+### Vladimir Sitnikov
+
+- compressed streams over network
+- "query response status" messages being sent in plain text (`insert 1`, `select 10`, etc.).
+Having some binary there would make things easier to parse.
+- unable to use prepared statements for `set "application_name"=...`, etc