[jboss-jira] [JBoss JIRA] Commented: (JBMESSAGING-1664) Ordering Group is broken on server restart when messages are paged and reloaded

[ https://jira.jboss.org/jira/browse/JBMESSAGING-1664?page=com.atlassian.ji... ] Howard Gao commented on JBMESSAGING-1664: ----------------------------------------- Currently I think I have two options. Option 1 is based on my current fix. To limit the memory when we fetch all the messages for a queue from DB, we can use Statement.setFetchSize(). Option 2 is that we split the query into two queries. First we query up to fullSize the messages for a Channel (queue), of which we can safely put those messages whose PAGE_ORD are null values into memory queue. Then we remember the number of messages (say n) having been loaded. Second we query all messages that have null PAGE_ORD values and, after dropping the first n messages, update their PAGE_ORD values. Option 1 is better. Option 2 is not so simple, as the first query may introduce new SQLs that have to use DB specific syntax. Here is the list of SQL for different DBs: SELECT * FROM T LIMIT 10 OFFSET 20 MySQL, PostgreSQL (also supports the standard, since version 8.4), SQLite, H2 SELECT * from T WHERE ROWNUM <= 10 Oracle (also supports the standard, since Oracle8i) SELECT FIRST 10 * from T Ingres SELECT FIRST 10 * FROM T order by a Informix SELECT SKIP 20 FIRST 10 * FROM T order by c, d Informix (row numbers are filtered after order by is evaluated. SKIP clause was introduced in a v10.00.xC4 fixpack) SELECT * FROM T FETCH FIRST 10 ROWS ONLY DB2 (also supports the standard, in Linux, Windows, and Unix since DB2 v8, z/OS support added in v9) SELECT TOP 10 * FROM T MS SQL Server (also supports the standard, since SQL Server 2005), Sybase ASE, MS Access SELECT TOP 10 START AT 20 * FROM T Sybase SQL Anywhere (also supports the standard, since version 9.0.1) SELECT FIRST 10 SKIP 20 * FROM T Interbase, Firebird SELECT * FROM T ROWS 20 TO 30 Firebird (since version 2.1) http://en.wikipedia.org/wiki/Select_(SQL) -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: https://jira.jboss.org/jira/secure/Administrators.jspa - For more information on JIRA, see: http://www.atlassian.com/software/jira