Thread: libpgtcl modifications
Well, I hacked some files to get the following working: A broken backend connection trigers a notify event to the client (fixed notification string "connection_closed") so proper action can be taken to switch to another database server etc. Remember that this is event driven. If you have applications, that have idle database connections most of the time, you'll get immediate feedback of a dying server. Upon connection to the server issue a pg_notify for notify event "connection_closed" and whenever the backend crashes (which it does do in very very rare cases) you get an event driven recovery. (of course the Tcl-Event loop has to be processed). Issuing a notification "connection_closed" on a still working database could be used for switching to another db-server. I'd like to share my changes (because I don't want to apply them to every release). What's the way to go ? I'd also like to see a TclObj-based implementation, and also support for Tcl8.4, *and* I'd even be willing to implement some of these changes. Any suggestions ? Attached is the patch with the described functionality. Oops , cannot attach files with google, and my ISP does'nt have comp.databases.postgresql.interfaces :-(, what shall I do ? My ISP says, this NG is not listed in the BIG8 groups, is that correct ? Gerhard >
Luke Myers wrote: > Gerhard Hintermayer wrote: > >> Attached is the patch with the described functionality. Oops , cannot >> attach files with google, and my ISP does'nt have >> comp.databases.postgresql.interfaces :-(, what shall I do ? My ISP >> says, this NG is not listed in the BIG8 groups, is that correct ? >> >> Gerhard >> > > Can you use news.postgresql.org? > > -- Luke Kale Myers > Indeed that works, and I even managed to use it with leafnode. Here's the patch (hope i did it right) -- Gerhard Hintermayer http://www.inode.at/g.hintermayer
Attachment
Can I have some description of what this patch does? --------------------------------------------------------------------------- Gerhard Hintermayer wrote: > Luke Myers wrote: > > Gerhard Hintermayer wrote: > > > >> Attached is the patch with the described functionality. Oops , cannot > >> attach files with google, and my ISP does'nt have > >> comp.databases.postgresql.interfaces :-(, what shall I do ? My ISP > >> says, this NG is not listed in the BIG8 groups, is that correct ? > >> > >> Gerhard > >> > > > > Can you use news.postgresql.org? > > > > -- Luke Kale Myers > > > > Indeed that works, and I even managed to use it with leafnode. > > Here's the patch (hope i did it right) > > > -- > Gerhard Hintermayer > http://www.inode.at/g.hintermayer [ application/x-gunzip is not supported, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Your patch has been added to the PostgreSQL unapplied patches list at: http://candle.pha.pa.us/cgi-bin/pgpatches I will try to apply it within the next 48 hours. --------------------------------------------------------------------------- Gerhard Hintermayer wrote: > Luke Myers wrote: > > Gerhard Hintermayer wrote: > > > >> Attached is the patch with the described functionality. Oops , cannot > >> attach files with google, and my ISP does'nt have > >> comp.databases.postgresql.interfaces :-(, what shall I do ? My ISP > >> says, this NG is not listed in the BIG8 groups, is that correct ? > >> > >> Gerhard > >> > > > > Can you use news.postgresql.org? > > > > -- Luke Kale Myers > > > > Indeed that works, and I even managed to use it with leafnode. > > Here's the patch (hope i did it right) > > > -- > Gerhard Hintermayer > http://www.inode.at/g.hintermayer [ application/x-gunzip is not supported, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Revision 2 was not so quick, but also not so dirty. Here's my first draft. I have modified: - Version number of Pgtcl changed to 1.4 (to reflect the additional command) - added a command pg_on_connection_loss Syntax: pg_on_connection_loss conn ?callback? Use no callback parameter to query the actuall callback script and with parameter to set/change callback. The callback is evaluated whenever the connection to the backend gets lost (eof condition ?). I do this by checking for a false return value from PQconsumeInput. Today I did some quick testing, no segfaults, no errors. Broken backends are detected both in idle connections and when you're in a COPY command (these are the two possibilities, where PQconsumeInput is called). I'm using the same readable fileevent on the database connection as pg_listen does internally. The structure Pg_ConnectionId was extended by two fields : char *conn_loss to store the callback and Tcl_Interp *interp to store the interpreter, in which context the callback will be evaluated. Can someone with more experience on Tcl event programming take a look at this, I mananged to write some Tcl extensions, but am new to modifying the Tcl event-loop. (what I did, was copying most of the pg_listen stuff). Basically PgStartNotifyEventSource() is called, when a callback proc is supplied to pg_on_connection_loss, which (unmodified) does install a readable fileevent on the db connection, then I check for false return value of PQconsumeInput and add a ConnLossEvent type to the event queue. (pg_)listen callbacks are deleted immediately from the the event queue when the db connection is broken, just like in the unpatch version. What This a point worth to discuss: Which commands will dump core when used in the disconnect handler ? pg_disconnect works, but the best thing might be to invoke pg_disconnect as the first command within the disconnect handler per default (in C code, not in Tcl) so possible subsequent operations on the just closed connection would at least trigger a "... is not a valid postgresql connection" error, but not run into any segfaults. I will do some more testing tomorrow, but since I only can post via google at work, I'd like to get some feedback more quickly. Gerhard PS: I need my patch also for an older version of Postgresql (7.0.2), can I copy the whole libpgtcl directory into the 7.0.2 source path without any risk ? -- Gerhard Hintermayer http://www.inode.at/g.hintermayer
Attachment
Last Thursday I posted revision 2 of my patch (directly to news.postgresql.org with *no* error). Unfortuntely it does not show up here. This are the longest 6 to 9 hours I've ever seen. I Will repost in the evening :-( Gerhard
Gerhard Hintermayer wrote: > Last Thursday I posted revision 2 of my patch (directly to > news.postgresql.org with *no* error). Unfortuntely it does not show up > here. This are the longest 6 to 9 hours I've ever seen. I Will repost > in the evening :-( > > Gerhard Damn, I posted that from the PC located at my girlfriend. Do'nt have the description I wrote (It was quite long). Btw, is there a more save way to do postings to comp.databases.postgresql.interfaces. I also do get strange replys from postmaster@afk.dk when I do post via Google ? Strange ! Here you have a short description, the long one you'll get when I'm at my other PC next time. I added a new command: pg_on_connection_loss conn ?callback? changed libpgtcl version to 1.4 to reflect the additional command. No callback to query the current script, with callback to set/change callback script. Script is executed whenever (all occurences of) PQconsumeInput return false, i.e. both in an idle database connection and while processing a COPY command. Tested a bit, no errors, alle db-operations in callback are allowed (and trigger a "is not a valid connection" or so error) Any comments ? -- Gerhard Hintermayer http://www.inode.at/g.hintermayer
Sorry, forgot the attachment. Here it is. -- Gerhard Hintermayer http://www.inode.at/g.hintermayer
Attachment
Your patch has been added to the PostgreSQL unapplied patches list at: http://candle.pha.pa.us/cgi-bin/pgpatches I will try to apply it within the next 48 hours. --------------------------------------------------------------------------- Gerhard Hintermayer wrote: > Gerhard Hintermayer wrote: > > Last Thursday I posted revision 2 of my patch (directly to > > news.postgresql.org with *no* error). Unfortuntely it does not show up > > here. This are the longest 6 to 9 hours I've ever seen. I Will repost > > in the evening :-( > > > > Gerhard > > Damn, I posted that from the PC located at my girlfriend. Do'nt have the > description I wrote (It was quite long). Btw, is there a more save way to do > postings to comp.databases.postgresql.interfaces. I also do get strange replys > from postmaster@afk.dk when I do post via Google ? Strange ! > > Here you have a short description, the long one you'll get when I'm at my other > PC next time. > > I added a new command: > > pg_on_connection_loss conn ?callback? > > changed libpgtcl version to 1.4 to reflect the additional command. > > No callback to query the current script, with callback to set/change callback > script. Script is executed whenever (all occurences of) PQconsumeInput return > false, i.e. both in an idle database connection and while processing a COPY > command. Tested a bit, no errors, alle db-operations in callback are allowed > (and trigger a "is not a valid connection" or so error) > > Any comments ? > > -- > Gerhard Hintermayer > http://www.inode.at/g.hintermayer > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Patch applied for 7.3. Thanks. --------------------------------------------------------------------------- Gerhard Hintermayer wrote: > Gerhard Hintermayer wrote: > > Last Thursday I posted revision 2 of my patch (directly to > > news.postgresql.org with *no* error). Unfortuntely it does not show up > > here. This are the longest 6 to 9 hours I've ever seen. I Will repost > > in the evening :-( > > > > Gerhard > > Damn, I posted that from the PC located at my girlfriend. Do'nt have the > description I wrote (It was quite long). Btw, is there a more save way to do > postings to comp.databases.postgresql.interfaces. I also do get strange replys > from postmaster@afk.dk when I do post via Google ? Strange ! > > Here you have a short description, the long one you'll get when I'm at my other > PC next time. > > I added a new command: > > pg_on_connection_loss conn ?callback? > > changed libpgtcl version to 1.4 to reflect the additional command. > > No callback to query the current script, with callback to set/change callback > script. Script is executed whenever (all occurences of) PQconsumeInput return > false, i.e. both in an idle database connection and while processing a COPY > command. Tested a bit, no errors, alle db-operations in callback are allowed > (and trigger a "is not a valid connection" or so error) > > Any comments ? > > -- > Gerhard Hintermayer > http://www.inode.at/g.hintermayer > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073