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e32f5a1fb1
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](https://github.com/hasura/pg-client-hs/pull/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.
27 lines
779 B
PL/PgSQL
27 lines
779 B
PL/PgSQL
CREATE TABLE hdb_catalog.hdb_schema_update_event (
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id BIGSERIAL PRIMARY KEY,
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instance_id uuid NOT NULL,
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occurred_at timestamptz NOT NULL DEFAULT NOW()
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);
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CREATE FUNCTION hdb_catalog.hdb_schema_update_event_notifier() RETURNS trigger AS
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$function$
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DECLARE
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instance_id uuid;
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occurred_at timestamptz;
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curr_rec record;
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BEGIN
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instance_id = NEW.instance_id;
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occurred_at = NEW.occurred_at;
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PERFORM pg_notify('hasura_schema_update', json_build_object(
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'instance_id', instance_id,
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'occurred_at', occurred_at
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)::text);
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RETURN curr_rec;
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END;
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$function$
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LANGUAGE plpgsql;
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CREATE TRIGGER hdb_schema_update_event_notifier AFTER INSERT ON hdb_catalog.hdb_schema_update_event
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FOR EACH ROW EXECUTE PROCEDURE hdb_catalog.hdb_schema_update_event_notifier();
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