essential FIX messages

Focus on just 2 app messages – new order single + a partial fill. Logon/Logout/heartbeat… LG2 — important session messages.

Start with just the 10 most common fields in each message. Later, you need to know 20 but no more.

For the most important fields – tag 35, exectype, ordstatus, focus on the most important enum values.

This is the only way to get a grip on this slippery fish

25-13:34:27:613440 |250—-> 16 BC_ITGC_14_CMAS_104 1080861988 |



— A NewOrderSingle followed by 2 exec reports —

25-13:34:27:802535 |<—-252 13 BC_ITGC_14_CMAS_104 1079105241 |



25-13:34:27:990564 |<—-253 13 BC_ITGC_14_CMAS_104 1079105241 |



achieving sub-millis latency – exchange connectivity

This post is about really achieving it, not “trying to achieve”.

First off, How do you measure or define that latency? I guess from the moment you get one piece of data at one end (first marker) to the time you send it out at the other end (2nd marker). If the destination is far away, then I feel we should use the ack time as the 2nd marker. There are 2 “ends” to the system being measured. The 2 ends are
* the exchange and
* the internal machines processing the data.

There are also 2 types of exchange data — order vs market data (MD = mostly other people’s quotes and last-executed summaries). Both are important to a trader. I feel market data is slightly less critical, though some practitioners would probably point out evidence to the contrary.

Here are some techniques brought up by a veteran in exchange connectivity but not the market data connectivity.
* Most places use c++. For a java implementation, most important technique is memory tuning – GC, object creation.
* avoid MOM! — HSBC algo trading IV
* avoid DB — local flat file is one way they use for mandatory persistence (execution). 5ms latency is possible. I said each DB stored proc or query takes 30-50 ms minimum. He agreed.
** A market data engineer at 2Sigma also said “majority of data is not in database, it’s in file format”. I guess his volume is too large for DB.
* object pooling — to avoid full GC. I asked if a huge hash table might introduce too much look-up latency. He said the more serious problem is the uncontrollable, unpredictable GC kick-in. He felt hash table look-up is probably constant time, probably pre-sized and never rehashed. Such a cache must not grow indefinitely, so some kind of size control might be needed.
* multi-queue — below 100 queues in each JVM. Each queue takes care of execution on a number of securities. Those securities “belong” to this queue. Same as B2B
* synchronize on security — I believe he means “lock” on security. Lock must attach to objects, so the security object is typically simple string objects rather than custom objects.
* full GC — GC tuning to reduce full GC, ideally to eliminate it.
* use exchange API. FIX is much slower, but more flexible and standardized. See other posts in this blog

Some additional techniques not specific to exchange connectivity —
$ multicast — all trading platforms use multicast nowadays
$ consolidate network requests — bundle small request into a large requests
$ context switching — avoid
$ dedicated CPU — If a thread is really important, dedicate a cpu to it.
$ shared memory — for IPC
$ OO overhead — avoid. Use C or assembly
$ pre-allocate large array
$ avoid trees, favour arrays and hash tables
$ reflection — avoid
$ concurrent memory allocator (per-thread)
$ minimize thread blocking
** immutable
** data parallelism
** lockfree

Fwd: design a finite state machine for a FIX engine

We need a cache of all the pending orders we created. All from-exchange FIX messages must match one of the pending orders. Once matched, we examine its current state.


If the message is belated, then we must reject it (informing all parties involved).


If the message is delivered out of sequence and too early, then we must keep it on hand. (a 2nd cache)


If the message is for immediate consumption, then consume.




the FSM in FIX is about state transition and should be pertinent to all state machines. Basically, it goes from pending new to new to fill or cancelled. From cancelled, it cannot go back to new or fill etc.



FIX^MOM untangled – exchange connectivity

The upshot — some subsystem use FIX not MOM; some subsystem use MOM not FIX. Some sites send FIX over MOM (such as RV) but not common.

It’s important to realize FIX is not a type of MOM system. Even though FIX uses messages, I believe they are typically sent over persistent TCP sockets, without any middle-ware.

Say we (sell-side or buy-side) have a direct connectivity to an exchange. Between exchange and our exterior gateway, it’s all sockets and possibly java NIO — no messaging. Data format could be FIX, or it could be the exchange’s proprietary format — here’s why.

The exchange often has an internal client-server protocol — the real protocol and a data flow “choke point” . All client-server request/response relies solely on this protocol. The exchange often builds a FIX translation over this protocol (for obvious reasons….) If we use their FIX protocol, our messages are internally translated from FIX to the exchange proprietary format. Therefore it’s obviously faster to directly pass messages in the exchange proprietary format. The exchange offers this access to selected hedge funds.

As an espeed developer told me, they ship a C-level dll (less often *.so [1]) library (not c++), to be used by the hedge fund’s exterior gateway. The hedge fund application uses the C functions therein to communicate with the exchange. This communication protocol is possibly proprietary. HotspotFX has a similar client-side library in the form of a jar. There’s no MOM here. The hedge fund gateway engine makes synchronous function calls into the C library.

[1] most trader workstations are on win32.

Note the dll or jar is not running in its own process, but rather loaded into the client process just like any dll or jar.

Between this gateway machine and the trading desk interior hosts, the typical communication is dominated by MOM such as RV, 29West or Solace. In some places, the gateway translates/normalizes messages into an in-house standard format.

design considerations – my first homemade FIX client

In a typical sell-side / market maker, the FIX gateway is a FIX client for a liquidity venue. The liquidity venue (typically an exchange, but also ECNs, dark pools) runs a massively multi-threaded, FIX server farm, possibly with custom-made FPGA hardware. I believe the technical requirements for an exchange FIX server is different from a sell-side FIX client.

Therefore, I assume my audience are far more interested in the client code than the server code.

My mock server implementation is a mock-up, with no optimization, no resilience/robust design, no fault-tolerance, no select()-based sockets, no high-availability, no checksum validation.

— design priorities —
Since this is a from-scratch implementation of a large spec, I focused on basic functionality. Debugging and instrumentation is important in the early stage. A lot of extra code was created to help developers verify the correct operation of all those nitty gritty details.

I don’t aim to build a complete engine, but the basic functionality I build, i try to build it on solid ground, so hopefully it doesn’t become throw-away code.

At the heart of the OO design was the abstraction expressed by AbstractClient, AbstractState and ClientSession. These form the backbone of the core object graph. The fields and constructors were chosen with care. Cohesion and low-coupling were my ideals but sometimes hard to achieve.

These core classes help meet most of the fundamental requirements related to object state of a client connection, sequence number, state transition, output stream sharing, connection liveness monitoring… I wouldn’t say these are well-design classes, but they are a reasonable first attempt at modelling the problem using java classes.

Reusable components were created whenever possible, such as the message parser, message formatter.

FIX engine are highly configurable. All config parameters are extracted into a config object, which is obtained from a config factory. One config for Test, one for Production or UAT etc.

— features —
– parsing a raw FIX msg into an array, which is faster to access than a hashmap. By our design, we avoid hash lookup completely.
– is a home-made solution to the potential forever-blocking of readLine(). On some platforms, socket read is not interruptible and the only way to unfreeze a socket read is to close the socket. We do that in this implementation but only after sending a final logout message.
– Various template methods to guarantee close() and guard against resource leak
– AbstractClient has most of the generic logic, while SingleOrderClient implements very small amount of custom logic.
– FIX msg formatter is generic enough to accept a map of tags and values — any tags and values
– sequence num validation
– state machines on both client and (simplified) server. State design pattern.
– server side — very few features, but ConnectionManager is reasonable encapsulation of new socket creation.

—- client-side features to be implemented —-
– heart beat — more robust. Should never fail.
– timeout waiting for ack
– re-logon if no heartbeat for 60 seconds
– checksum validation
– storing exchange order-ack into database
– Right now, given time constraint, i didn’t use nonblocking IO. All FIX system should use non-blocking IO.
———- Disclaimer ————-
I spent about 4 hours on this project, as suggested by Jonathan. I had to do some basic research on FIX since I have never programmed FIX (except some ECN connectivity modules that probably used FIX under the hood).
————— How to run the server/client —————–
Run, then
To see the heart beat monitoring/intervention (Destroyer) in action, put 500 in getSilenceThreshold().

top 10 fields in NOS ^ exec report

—- top 5 fields common to NOS (NewOrderSingle) and exec report —
#1) 22 securityIDSource. Notable enum values
5 = RIC code
*** 48 SecurityID, Requires tag 22 ==NOS/exec
*** 55 optional human-readable symbol ==NOS/exec

#2) 54 side. Notable enum values
1 = Buy
2 = Sell

#3) 40 ordType. Notable enum values
1 = Market order
2 = Limit order

#4) 59 TimeInForce. Notable enum values
0 = Day (or session)
1 = Good Till Cancel (GTC)
3 = Immediate Or Cancel (IOC)
4 = Fill Or Kill (FOK)

—- other fields common to NOS and exec type
*11 ClOrdID assigned by buy-side
*49 senderCompID
*56 receiving firm ID
*38 qty
*44 price

—- exec report top 5 fields
* 150 execType
* 39 OrdStatus. Notable enum values
0 = New
1 = Partially filled
2 = Filled

* OrderID assigned by sell-side. Not in NOS. Less useful than the ClOrdID

ECN – 2 core services – quote aggregation^execution

2 core functions of a liquidity venue
Q) quote collection — including dissemination. Consider a BBS.
Q2) RFQ — not needed on exchanges.
E) execution

(Most fundamental messages are quotes and orders.)

An exchange offers additional services (such as integrity, credit guarantee…) but most ECNs offer only these 2 core services.

Typically each quote (similar to a limit order) received is assigned a quoteID. Each order must reference an orderID, so the liquidity venue can forward the order to the quote originator. The originator always has the option to reject, even if the quote is advertized as “firm”.

Such a liquidity venue typically holds no inventory and takes no position hence zero risk.

Most of these liquidity venues support FIX. They might support another messaging protocol too.

socket, tcp/udp, FIX

I was told both UDP and TCP are used in many ibanks. I feel most java shops generally prefer the simpler TCP.
Specifically, I learnt from many veterans that some ibanks use multicast (UDP) for internal messaging.

FIX is not much used. It is sometimes used as purely message formatting protocol (without any session management) on top of multicast UDP. (In contrast, full-featured FIX communication probably prefer TCP for connection/session control.)

Similar – Object serialization like protobuf.

##essential features of FIX session

Top 5 session-message types– Heartbeat(0), Test Request(1) ResendRequest(2), Logout(5) / Logon(A).[1] This short list highlight the essential functionality of the concept known as “FIX session”. I feel the most important features are sequence number and heart beat.

FIX session concept is different from a database server session. I feel FIX session is more like a TCP connection. says A FIX Session can be defined as “a bi-directional stream of ordered messages between two parties within a continuous sequence number series”

Each FIX Engines is expected to keep track of both sequence numbers, including The Incoming Sequence Number expected on inbound messages received from the counterparty is a blog post by a fellow developer in finance IT. is another blogger

[1] In parentheses are MsgType values, which are ALWAYS single-characters.

quickly parse a FIX message into key/value pairS is the context.

     * Parsing to array is faster than parsing to a HashMap
    public static ArrayList quickParse(String fromServer) {
        ArrayList ret = new ArrayList(Collections.nCopies(
            MAX_FIX_TAG, (String) null));
        for (String pair : fromServer.split(SOH)) {
            String[] tmp = pair.split(“=”);
            if (tmp.length != 2)  continue;
            int tag = Integer.parseInt(tmp[0]);
            ret.set(tag, tmp[1]); //treat ArrayList as array — efficient
        return ret;