pgwire: lower the max repeated error count before closing a connection

In 39067de we added behavior to give up and close a network connection
if a threshold of repeated errors was reached. It retried on errors
since some network errors could be transient.

It was retrying tens of thousands of times, which is excessive. We lower
this to 256 now. This is motivated by a few tests that identifed the
error handling logic in this tight loop being quite expensive. Retrying
fewer times means that we'll reduce CPU usage during failure scenarios.

Release note: None

Author: rafiss

pkg/sql/pgwire/server.go

@@ -1075,7 +1075,7 @@ func (s *Server) newConn(
 // maxRepeatedErrorCount is the number of times an error can be received
 // while reading from the network connection before the server decides to give
 // up and abort the connection.
-const maxRepeatedErrorCount = 1 << 15
+const maxRepeatedErrorCount = 1 << 8
 
 // serveImpl continuously reads from the network connection and pushes execution
 // instructions into a sql.StmtBuf, from where they'll be processed by a command