[pgpool-general: 5425] ERROR: unable to read data from frontend

[Yates, James C. -ND]

Versions:  OS  Centos 6.8
                PgPool  3.5.0
               Postgres 9.4.4

Intermittently we see these errors in the pgpool log file:
2017-04-17 20:40:54: pid 23448: ERROR:  unable to read data from frontend
2017-04-17 20:40:54: pid 23448: DETAIL:  socket read failed with an error "Connection reset by peer"


On the client it looks like:

server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
The connection to the server was lost. Attempting reset:

Client uses Ruby/Rails to connect, but I see the same issue using psql.

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