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add postgres notify listener #5

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merged 4 commits into from
Feb 6, 2019
Merged

add postgres notify listener #5

merged 4 commits into from
Feb 6, 2019

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rakeshkky
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Exposes a function listen via a new module Database.PG.Query.Listen to allow listening
through a channel

@0x777 0x777 merged commit 2d0e9f4 into hasura:master Feb 6, 2019
@rakeshkky rakeshkky mentioned this pull request Feb 8, 2019
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shahidhk pushed a commit to hasura/graphql-engine that referenced this pull request Mar 12, 2019
@rakeshkky @shahidhk
sync metadata cache across multiple instances connected to same db (c…
e32f5a1 
…loses #1182) (#1574)

1. Haskel library `pg-client-hs` has been updated to expose a function that helps listen to `postgres` notifications over a `channel` in this [PR](hasura/pg-client-hs#5)
2. The server records an event in a table `hdb_catalog.hdb_cache_update_event` whenever any `/v1/query` (that changes metadata) is requested. A trigger notifies a `cache update` event via `hasura_cache_update` channel
3. The server runs two concurrent threads namely `listener` and `processor`. The `listener` thread listens to events on `hasura_cache_update` channel and pushed into a `Queue`. The `processor` thread fetches events from that `Queue` and processes it. Thus server rebuilds schema cache from database and updates.
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@0x777 0x777 0x777 approved these changes

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@rakeshkky @0x777