Re: [PDO] PostgreSQL auto-reconnect in PDO contructor for permanent connections: request for comments

Marc Barilley wrote:
> Here is a diff with my patch. It's in the -Bur format. Any comment is
> welcome.
> 
> What it does is:
> - define a new constant PDO::PGSQL_ATTR_PING_CONNECTION for the
> driver-specific attributes
> - this can be set to true or false ; default is true

I'm still -1 on a driver-specific attribute.  Similar functionality
could be useful for other drivers so why not have a generic attribute?

Chris

> - when set to true, it makes the driver perform a "select 1" on the link
> to thoroughly test the connection
> 
> 
> Marc
> 
> 
> 
> Wez Furlong a écrit :
>> Honestly, the driver is broken if it does not correctly detect a dead
>> connection, or if it blocks indefinitely.  It doesn't really matter
>> what the user wants in that case; what they get is unusable without
>> manually taking the same steps in their code.
>>
>> The postgres API is blocking by default.  You can configure a timeout
>> in your connection string, but this does not apply to all cases (only
>> connection time, IIRC).  In all other cases, the calls can block, and
>> can block indefinitely depending on the nature of the disconnect, the
>> locality of the server, the nature of the network hardware between the
>> client and the server.
>>
>> --Wez.
>>
>> On Mar 31, 2010, at 7:25 PM, Marc Barilley wrote:
>>
>>> I don't think this is a bug per se, just a missing feature. Some
>>> programmers may want a thorough check of the connection while some
>>> may not. Both have their benefits and drawbacks. I think it is up to
>>> the programmer to choose if the connection needs to be checked or not.
>>> I'm curious to know if you have more precise informations about the
>>> conditions when the API can block. This could help :) Thank you.
>>>
>>> Marc
>>>
>>>
>>> Wez Furlong a écrit :
>>>> This thread started out as a bug report with the liveness check in
>>>> the postgres driver; the mechanism I'm using in an internal project,
>>>> which is similar in architecture to PDO, is this, which has the
>>>> advantage of not being a blocking operation--I've seen the postgres
>>>> API block indefinitely in some stale/retired connection cases.  This
>>>> code will give 5 attempts up to 5 seconds each to determine if the
>>>> connection is still viable.
>>>>
>>>> --Wez.
>>>>
>>>>  int tries = 5;
>>>>  PGresult *res;
>>>>  struct pollfd pfd;
>>>>  GET_DRV(drv);
>>>>
>>>>  PQsendQuery(D->server, "SELECT 1;");
>>>>
>>>>  while (tries--) {
>>>>    res = PQgetResult(D->server);
>>>>    if (res) {
>>>>      break;
>>>>    }
>>>>    pfd.fd = PQsocket(D->server);
>>>>    pfd.events = POLLIN|POLLHUP|POLLERR;
>>>>    poll(&pfd, 1, 5000);
>>>>  }
>>>>  if (res && PQstatus(D->server) == CONNECTION_OK) {
>>>>    PQclear(res);
>>>>    return 1;
>>>>  }
>>>>  if (res) {
>>>>    PQclear(res);
>>>>  }
>>>>  PQreset(D->server);
>>>>  return 0;
>>>>
>>>>
>>>>
>>
>>
>>
> 

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