On 14 February 2018 at 10:26, Andres Freund <and...@anarazel.de> wrote:
> On 2018-02-14 11:12:30 +0900, Tatsuo Ishii wrote: > > According to the manual, backend sends a parameter status message when > > certain configuration variable has been changed and SIGHUP signal is > sent. > > https://www.postgresql.org/docs/10/static/protocol-flow. > html#PROTOCOL-ASYNC > > > > ParameterStatus messages will be generated whenever the active value > > changes for any of the parameters the backend believes the frontend > > should know about. Most commonly this occurs in response to a SET > > SQL command executed by the frontend, and this case is effectively > > synchronous ― but it is also possible for parameter status changes > > to occur because the administrator changed a configuration file and > > then sent the SIGHUP signal to the server. > > > > So I connected to PostgreSQL using psql and attached strace to psql. > > Then I changed standard_conforming_strings and executed pg_ctl > > reload. The PostgreSQL log shows: > > > > 12073 2018-02-14 11:05:22 JST LOG: received SIGHUP, reloading > configuration files > > 12073 2018-02-14 11:05:22 JST LOG: parameter > "standard_conforming_strings" changed to "off" > > 12073 2018-02-14 11:05:22 JST DEBUG: sending signal 1 to process 12158 > > > > But as far as strace tells, nothing was sent to psql. Is this expected? > > It'll only get sent to the client the next time the server processes a > query. We can't just at arbitrary points reload the config file or send > messages out. The SIGHUP handler just sets ConfigReloadPending which > PostgresMain() then processes: > > /* > * (6) check for any other interesting events that > happened while we > * slept. > */ > if (ConfigReloadPending) > { > ConfigReloadPending = false; > ProcessConfigFile(PGC_SIGHUP); > } > > which'll then, in turn, send out ParameterStatus messages for changed > GUC_REPORT GUCs. I was wondering a while ago - can't we just set our own proc's latch here, so we wake up and send it earlier if we're in the idle main loop? -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
