I have a table that I want to use as a queue with all functionality (Insert, update, delete) embodied in a stored procedure. Inserts and deletes are no problem. An external program would call the stored procedure to get one or more emails to work on, selecting on “state=’N’”, then updating the row so “state=’P’”. My problem is having multiple threads calling the stored procedure simultaneously and getting the same row(s). Selecting FOR UPDATE won’t work as, if thread #1 gets 3 rows and thread #2 starts before thread #1 completes (Commits), thread #2 will select the same 3 rows as thread #1 except, since thread #1 will update the state (changing the state to ‘P’) so that those rows no longer meet thread #2 criteria, and thread #2 will receive zero rows. The table looks like:
CREATE TABLE dss.stage_email
(
emailid bigserial NOT NULL,
email_path text,
state character(1) DEFAULT 'N'::bpchar, -- N = New Email, P=Processing, D=Deleting
fetch_date timestamp without time zone DEFAULT now(),
ingest_date timestamp without time zone
)
Steve Erickson
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