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 Senior Developer 266 East 7th Street, Floor 4 Saint Paul, MN 55101 651.925.3237 office 612.242.1343 cell NOTICE: This email, including any attachments, is covered by the Electronic Communications Privacy Act, is confidential and may be legally privileged. If you are not the intended recipient, you are hereby notified that any retention, dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please immediately notify our office by return email or at our telephone number (651) 925-3200. Then delete and destroy all copies of this email and any attachments. Thank you. |
