Thread: triggering an external action
I am trying to find the best way for a database trigger to signal a client process to take an action. Specifically, I am working on the classic problem of creating and modifying system accounts based on the updates to a "person registry" database. The basic model I'm working with has triggers on my tables of interest that stick a person's unique ID into a "todo queue" table whenever modifications are made. The queue is periodically polled by a script which processes and deletes each "todo" record. The polling script goes to sleep for gradually increasing periods of time whenever it polls the queue and finds it empty. What I want is a trigger on the "todo" table that will "kick" my processing script to make it wake up and process the queue immediately. In an Oracle environment, I think I could use adatabase pipe to achieve more or less the behavior I'm looking for, but I can't find anything that does what I want in pgsql at the database level. I could write a trigger in C or Perl or something that would do something at the OS level, like send a signal, but when I go down that path I start having to deal with unix issues like having to elevate to root privs to send a signal to a process that isn't running as the pgsql user, etc. It is doable but gets complex quickly. Is there anything I'm missing at the database level that would help me process updates in realtime? (And if not, which of the other mailing lists would be the most appropriate place for me to discuss the best way to implement an OS-level solution?) Thanks, -jbp -- Jay Parker - UALR Computing Services - Networks Project Manager jbparker@ualr.edu - http://www.ualr.edu/jbparker - 501-569-3345 But I have promises to keep, And miles to go before I sleep. -Frost
Jay Parker wrote: > I am trying to find the best way for a database trigger to signal a > client process to take an action. > > Specifically, I am working on the classic problem of creating and > modifying system accounts based on the updates to a "person registry" > database. > > The basic model I'm working with has triggers on my tables of interest > that stick a person's unique ID into a "todo queue" table whenever > modifications are made. The queue is periodically polled by a script > which processes and deletes each "todo" record. The polling script goes > to sleep for gradually increasing periods of time whenever it polls the > queue and finds it empty. > > What I want is a trigger on the "todo" table that will "kick" my > processing script to make it wake up and process the queue immediately. > In an Oracle environment, I think I could use a database pipe to > achieve more or less the behavior I'm looking for, but I can't find > anything that does what I want in pgsql at the database level. > > I could write a trigger in C or Perl or something that would do > something at the OS level, like send a signal, but when I go down that > path I start having to deal with unix issues like having to elevate to > root privs to send a signal to a process that isn't running as the pgsql > user, etc. It is doable but gets complex quickly. > > Is there anything I'm missing at the database level that would help me > process updates in realtime? (And if not, which of the other mailing > lists would be the most appropriate place for me to discuss the best way > to implement an OS-level solution?) > > Thanks, > > -jbp > How about LISTEN and NOTIFY, would they work for this? -- _______________________________ This e-mail may be privileged and/or confidential, and the sender does not waive any related rights and obligations. Any distribution, use or copying of this e-mail or the information it contains by other than an intended recipient is unauthorized. If you received this e-mail in error, please advise me (by return e-mail or otherwise) immediately. _______________________________
>I am trying to find the best way for a database trigger to signal a >client process to take an action. > >Specifically, I am working on the classic problem of creating and >modifying system accounts based on the updates to a "person registry" >database. > >The basic model I'm working with has triggers on my tables of interest >that stick a person's unique ID into a "todo queue" table whenever >modifications are made. The queue is periodically polled by a script >which processes and deletes each "todo" record. The polling >script goes >to sleep for gradually increasing periods of time whenever it >polls the >queue and finds it empty. > >What I want is a trigger on the "todo" table that will "kick" my >processing script to make it wake up and process the queue >immediately. > In an Oracle environment, I think I could use a database pipe to >achieve more or less the behavior I'm looking for, but I can't find >anything that does what I want in pgsql at the database level. > >I could write a trigger in C or Perl or something that would do >something at the OS level, like send a signal, but when I go down that >path I start having to deal with unix issues like having to elevate to >root privs to send a signal to a process that isn't running as >the pgsql >user, etc. It is doable but gets complex quickly. > >Is there anything I'm missing at the database level that would help me >process updates in realtime? (And if not, which of the other mailing >lists would be the most appropriate place for me to discuss >the best way >to implement an OS-level solution?) This sounds like a job for LISTEN/NOTIFY: http://www.postgresql.org/docs/8.0/static/sql-listen.html http://www.postgresql.org/docs/8.0/static/sql-notify.html //Magnus
On 05/17/2005 01:07 PM, Bricklen Anderson wrote: > How about LISTEN and NOTIFY, would they work for this? Yes, that is precisely what I need... and what I have somehow overlooked during at least a dozen passes through the docs. Sigh. Thanks for your help, -jbp -- Jay Parker - UALR Computing Services - Networks Project Manager jbparker@ualr.edu - http://www.ualr.edu/jbparker - 501-569-3345 But I have promises to keep, And miles to go before I sleep. -Frost