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pageserver: disconnect when asking client to reconnect (#9390)

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## Problem

Consider the following sequence of events:
1. Shard location gets downgraded to secondary while there's a libpq
connection in pagestream mode from the compute
2. There's no active tenant, so we return `QueryError::Reconnect` from
`PageServerHandler::handle_get_page_at_lsn_request`.
3. Error bubbles up to `PostgresBackendIO::process_message`, bailing us
out of pagestream mode.
4. We instruct the client to reconnnect, but continue serving the libpq
connection. The client isn't yet aware of the request to reconnect and
believes it is still in pagestream mode. Pageserver fails to deserialize
get page requests wrapped in `CopyData` since it's not in pagestream
mode.

## Summary of Changes

When we wish to instruct the client to reconnect, also disconnect from
the server side after flushing the error.

Closes https://github.com/neondatabase/cloud/issues/17336
This commit is contained in:
Vlad Lazar
2024-10-18 13:38:59 +01:00
committed by GitHub
parent fecff15f18
commit ec6d3422a5
1 changed files with 14 additions and 0 deletions
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14
libs/postgres_backend/src/lib.rs
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@@ -738,6 +738,20 @@ impl<IO: AsyncRead + AsyncWrite + Unpin> PostgresBackend<IO> {
QueryError::SimulatedConnectionError => {
return Err(QueryError::SimulatedConnectionError)
}
err @ QueryError::Reconnect => {
// Instruct the client to reconnect, stop processing messages
// from this libpq connection and, finally, disconnect from the
// server side (returning an Err achieves the later).
//
// Note the flushing is done by the caller.
let reconnect_error = short_error(&err);
self.write_message_noflush(&BeMessage::ErrorResponse(
&reconnect_error,
Some(err.pg_error_code()),
))?;
return Err(err);
}
e => {
log_query_error(query_string, &e);
let short_error = short_error(&e);