Brandon Simmons c425b554b8 server(events): utilize proper backpressure scheme (close #3839) (#4013) ... * Test working through a backlog of change events * Use a slightly more performant threaded http server in eventing pytests This helped locally but not on CI it seems... * Rework event processing for backpressure. Closes #3839 With loo low `HASURA_GRAPHQL_EVENTS_FETCH_INTERVAL` and/or slow webhooks and/or too small `HASURA_GRAPHQL_EVENTS_HTTP_POOL_SIZE` we might previously check out events from the DB faster than we can service them, leading to space leaks, weirdness, etc. Other changes: - avoid fetch interval sleep latency when we previously did a non-empty fetch - prefetch event batch while http pool is working - warn when it appears we can't keep up with events being generated - make some effort to process events in creation order so we don't starve older ones. ALSO NOTE: HASURA_GRAPHQL_EVENTS_FETCH_INTERVAL changes semantics slightly, since it only comes into play after an empty fetch. The old semantics weren't documented in detail, so I think this is fine.		2020-03-11 11:57:31 +05:30
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manual	server(events): utilize proper backpressure scheme (close #3839) (#4013)	2020-03-11 11:57:31 +05:30