OpenMAMA Data Quality as pluggable libs
Alpert, Reed <reed.alpert@...>
I've been looking at the data quality (dq) code and have some ideas on how to support multiple dq strategies.
Generally mama has a dq strategy built into dqstrategy.c, subscription.c, and transport.c that supports:
· SeqNums being present from the publisher to detect gaps and request recaps.
· SenderIds being present from the publisher and used for FT takeover.
· Initial/Recap pre-cache to correctly order an initial/recap and updates.
· Various config parameters for how the app should handle dq issues:
o Transport bounces and setting subs stale.
o Duplicate msgs.
o When to apply pre-cache.
o Handle initials (requiresInitial).
o Turn on/off dq (recoverGaps).
In order to provide additional dq strategies it is proposed:
· Move any code that references dq variables into dqstrategy.c. This is largely done, but there is some code in subscription.c that can be moved.
· Make all dq structures opaque so they are only visible via methods.
· Turn dqstrategy.c into a pluggable dq bridge, using entitlements as a model.
At this point current impl will be the default pluggable dq bridge, so the same behavior as now will be observed, and additional pluggable dq libs can be developed.
There is also the code in transport.c that handles transport bounces. This needs to be defined as to what service it provides for the bridges.
· When a transport disconnects it can notify the app via a transport callback, and also each sub on the transport via stale/maybeStale.
· When a transport reconnects it can notify the app via a transport callback, and also each sub via quality=OK, and requesting a recap.
It may be helpful to create an mDQTransport struct to hold transport-specific dq vars.
Attached is the beginnings of a state diagram for dq - it is a bit busy, but I think will be helpful in determining what does happen. Note that this does have paths for the code we added to send stale to subs even if dq is turned off. The red text/lines are for the 99.9% use case.
Any comments or ways forward please contribute.
Reed Alpert | Corporate & Investment Bank | Market Data Services | J.P. Morgan | 4 Metrotech Center, 23rd Floor, Brooklyn, NY 11245 | T: 718.242.5198 | M: 917.414.4613 | reed.alpert@...
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