I'm jumping in a bit late, but last year I filed a tar due to an enqueue hash chains latch problem (related to a deadlock). But you didn't mention a deadlock so this probably has nothing at all to do with your issue. From the description (8.1.7.4.1 on Win2k BTW): --- --- User runs a program to load data into the DB. At a certain point, this causes an ORA-00060 (deadlock). So far no real problem, but a few minutes later (while deadlock cleanup is still going on), every other session in the DB hangs until deadlock cleanup is completed. 10046 traces of the hanging processes show that they are all waiting on 'latch free'; trace files contain almost nothing but lines of the type : ... WAIT #6: nam='latch free' ela= 207 p1=635234948 p2=13 p3=136 WAIT #6: nam='latch free' ela= 206 p1=635234948 p2=13 p3=137 WAIT #6: nam='latch free' ela= 206 p1=635234948 p2=13 p3=138 WAIT #6: nam='latch free' ela= 207 p1=635234948 p2=13 p3=139 WAIT #6: nam='latch free' ela= 206 p1=635234948 p2=13 p3=140 ... The latch with number p2=13 is the 'enqueue hash chains' latch. --- --- And Oracle's answer : --- --- The problem you see is when the ora-60 error will generate an systemstate dump automatically. Then we need to take enqueue locks of the structure and this is causing your problems. This behaviour can be changed by setting event 10027 in your init.ora file, Put this is your init.ora file. --- --- mvg/regards Jo "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx> Sent by: oracle-l-bounce@xxxxxxxxxxxxx 01/09/2005 23:40 Please respond to jonathan To: <oracle-l@xxxxxxxxxxxxx> cc: Subject: Re: what's mean of "enqueue hash chains" latch? Note also how: enqueue gets and releases = 23M db block gets = 23 M execute count = 23M You can't help feeling that that's not a complete coincidence. I think your trigger theory sounds quite good at the moment, only a) I'd like to find that 23M executions in v$sql. Why isn't it appearing in statspack ? b) There's no redo generated to match the volume of locking. I'd like to see the snapshot of x$ksqst One thought - for parallel DML, maybe there are lots of DX locks being taken and dropped. Regards Jonathan Lewis http://www.jlcomp.demon.co.uk/faq/ind_faq.html The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/seminar.html Public Appearances - schedule updated Dec 23rd 2004 ----- Original Message ----- From: "Riyaj Shamsudeen" <rshamsud@xxxxxxxxxxxx> To: <oracle.unix@xxxxxxxxx>; <jonathan@xxxxxxxxxxxxxxxxxx> Cc: <oracle-l@xxxxxxxxxxxxx> Sent: Sunday, January 09, 2005 9:09 PM Subject: RE: what's mean of "enqueue hash chains" latch? Eygle Looking at the excel spreadsheet, one of the child latch has 2.4 Billion gets and other child latches have less then 76K latch gets. So, sessions are contending to lock one table. Looking at the statspack report, you have numerous enqueue gets and releases too. Is there any foreign key constraint on this table ? If yes, do you have any index on that foreign key column ? Further, what mode locks are being acquired ? do you have any triggers on this table, by any chance ? Thanks Riyaj "Re-yas" Shamsudeen Certified Oracle DBA -- //www.freelists.org/webpage/oracle-l -- //www.freelists.org/webpage/oracle-l