New mode for SuperServer run
----------------------------
Key: CORE-5912
URL: http://tracker.firebirdsql.org/browse/CORE-5912
Project: Firebird Core
Issue Type: New Feature
Reporter: Basil A. Sidorov
Note: my native lang is Russian, but I can read "simple English".
Proposal.
Add new mode for run Firebird 3+ SuperServer, called (for example)
"MultiServer".
In this mode Firebird server should work as two part - single "Dispatcher" and
many "Engine".
Each Engine work in separate OS process and serve only one database (but all
users on that database).
Dispatcher accept network connections, extract database name or alias from
parameter block and redirect (whole) connection stream to (some) Engine.
Dispatcher may pre-run Engine based on content aliases.conf (databases.conf)
and offer gracefull Engine shutdown on change content aliases./databases.conf
Goal.
Make possible isolation whole SuperServer from craches on single database,
separate metadata cache, better localization buffer cache and better handle
databases with different parameters and load type.
Disadvantage.
Additional work, grow resource usage.
Suggested (cross-platform) implementation based on local TCP-connections. Long
read.
Command line:
"fbserver -0x0000 ..." run dispatcher (dots are omitted arguments).
"fbserver -0xNUMBER [CONFIG]" - run engine (square brackets - optional
arguments).
NUMBER is (strictly) four HEX-digits for Dispathcer communation port.
CONFIG, if specified, coded as UTF-8 string and use instead firebird.conf.
Protocol:
Distpatcher and Engine communicate via simple text protocol with (short)
fixed-length message (eight octets).
Message is UTF-8 string in format '0x####CRLF', where: '0x' - fixed prefix,
#### - four HEX-digit, CRLF - fixed suffix (canonical EOL: two octet - 0x0D and
0x0A in that order).
Dispatcher send to Engine message with port number of listening socket for each
client steam.
Engine informs Dispatcher from wich ports Engine can be make connections. Not
pair "Dispath:Engine" - simply (unordered) set of engine-side ports numbers.
Dispatcher and Engine use only localhost and port numbers, assigned by IP-stack.
Dispatcher should check engine-side PID (local) connection and close "aliens".
Engine should reject client stream from Dispatcher, if database name/alias
differ from previous processed streams.
Long (and possible inaccurate) description:
Dispatcher request from OS listening socket (localhost:0).
On succes, Dispatcher remember port, which OS assign for this socket and use
that port number for communicate with all Engine.
On start, Engine parse command line for communication port and CONFIG (if
specified). Engine parse CONFIG (or firebird.conf) and so on.
After initial setup, Engine make connection on Dispatcher communication port,
write "greeting" message (0x0000CRLF), call flush() and go into wait state.
On fatal error of initial setup, Engine connect to Dispatcher and immediately
call "shutdown output" on socket. After read EOF from Dispatcher, Engine call
"shutdown input", make cleanup and exit with (some) error code.
If no response from Dispatcher within reasonable time (about five minutes),
Engine call "shutdown socket", cleanup and exit with error.
If network call is impossible or unsuccessfull - Engine simlpy cleanup and exit
with error.
After receive connection and check engine-side PID, Dispatcher or close
"aliens" or read "greeting".
Dispatcher write "confirmation" message (0x0000CRLF), call flush() and place
"Control Channel" into communication pool.
On very first (remote) client connection, Dispatcher peek database name/alias
from parameter block, select (some) "Control Channel" from communication pool
and create "Data Channel".
For "Data Channel" Dispatcher request from OS listening socket (localhost:0).
On success, Dispather send message to Engine with port number, assigned OS for
that socket.
Dispatcher may write several message and send whole set by single flush() call.
Engine bind socket with "localhost:Dispatcher-DataPort / localhost:0". On
success, Engine send info message with new port number to Dispatcher.
Engine may write several message and send it by single flush() call, but may
not make connection with "new" engine-side port(s) before return from flush()
call.
If, after initial greeting/confirmation message exchange, Dispatcher or Engine
send again message with zero port number (0x0000CRLF) - it is flag for
gracefull shutdown on service (that) database/Engine.
In gracefull shutdown state, Dispatcher should reject new client connections
for database, but should transfer data on existing (client) connections and
(Engine) "Data Channels".
After disconnect (in any way) all clients, Engine should call "shutdown output"
on sockets of "Data Channels".
After read EOF from Dispatcher, Engine should call "shutdown input" and make
resource cleanup.
If all client stream closed (in any way), Engine may gracefully close "Control
Channel" end exit.
If gracefull shutdown requested by Dispatcher, Engine must gracefully close
"Control Channel" and exit.
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