Re: How are rollback segments assigned?
Thanks Jared, thats not what I see. I have 20 rollback segments, and at no point in time, there were more than 4 transactions in the rollback segments. In fact, I happened to see it a couple of minutes ago. select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and 2 in one of them. And I have got alerts in place to alert me when there are more than 4 transactions in all of the rollback segments. And yeah, the rollback segments are online. Remains a mystery to me. Raj Jared.Still@r adisys.com To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] Sent by: cc: root@fatcity.Subject: Re: How are rollback segments assigned? com November 25, 2002 08:59 PM Please respond to ORACLE-L Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command
Re: How are rollback segments assigned?
Raj, You're assuming that the transactions are lasting long enough for you to catch them in the rollback segments. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/26/2002 09:42 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:Re: How are rollback segments assigned? Thanks Jared, thats not what I see. I have 20 rollback segments, and at no point in time, there were more than 4 transactions in the rollback segments. In fact, I happened to see it a couple of minutes ago. select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and 2 in one of them. And I have got alerts in place to alert me when there are more than 4 transactions in all of the rollback segments. And yeah, the rollback segments are online. Remains a mystery to me. Raj Jared.Still@r adisys.com To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] Sent by: cc: root@fatcity.Subject: Re: How are rollback segments assigned? com November 25, 2002 08:59 PM Please respond to ORACLE-L Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing
RE: How are rollback segments assigned?
Exactly. A guy might have to poll V$ROLLSTAT 100+ times per second to see the allocations happening on a system with well-designed transactions. You just can't do that with SQL. Raj, you *can* test the behavior by using some artificially *bad* transactions. On a quiescent system (nothing else running) with n rollback segments, open n+1 sqlplus sessions. In each session, update a row but don't commit. After each session's update, look at V$ROLLSTAT. To the best of my knowledge, the assignment algorithm has always been to assign a new txn to the segment with the smallest number of active txns in it. There are of course lots of ties (e.g., lots of segments might have 0 active txns in them). The tie-breaker in v6 was to assign in round-robin order (as the segments are listed in the init.ora file). In v7, the tie-breaker algorithm apparently changed to choose the segment that is listed earliest in the init.ora file. I don't know whether it changed again in 8 or 9. You'll know if you do the test. Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - Hotsos Clinic, Dec 9-11 Honolulu - Hotsos Clinic 101, Jan 7-9 Knoxville - Steve Adams's Miracle Master Class, Jan 13-15 Copenhagen - 2003 Hotsos Symposium, Feb 9-12 Dallas -Original Message- [EMAIL PROTECTED] Sent: Tuesday, November 26, 2002 12:25 PM To: Multiple recipients of list ORACLE-L Raj, You're assuming that the transactions are lasting long enough for you to catch them in the rollback segments. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/26/2002 09:42 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:Re: How are rollback segments assigned? Thanks Jared, thats not what I see. I have 20 rollback segments, and at no point in time, there were more than 4 transactions in the rollback segments. In fact, I happened to see it a couple of minutes ago. select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and 2 in one of them. And I have got alerts in place to alert me when there are more than 4 transactions in all of the rollback segments. And yeah, the rollback segments are online. Remains a mystery to me. Raj Jared.Still@r adisys.com To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] Sent by: cc: root@fatcity.Subject: Re: How are rollback segments assigned? com November 25, 2002 08:59 PM Please respond to ORACLE-L Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat
RE: How are rollback segments assigned?
Raj, Not to be too obvious, but... Are there any transactions that are being explicitly assigned to the rollback segments by the user/application? -Original Message- Sent: Tuesday, November 26, 2002 10:42 AM To: Multiple recipients of list ORACLE-L Thanks Jared, thats not what I see. I have 20 rollback segments, and at no point in time, there were more than 4 transactions in the rollback segments. In fact, I happened to see it a couple of minutes ago. select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and 2 in one of them. And I have got alerts in place to alert me when there are more than 4 transactions in all of the rollback segments. And yeah, the rollback segments are online. Remains a mystery to me. Raj Jared.Still@r adisys.com To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] Sent by: cc: root@fatcity.Subject: Re: How are rollback segments assigned? com November 25, 2002 08:59 PM Please respond to ORACLE-L Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Fink, Dan INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services
RE: How are rollback segments assigned?
In v7, the tie-breaker algorithm apparently changed to choose the segment that is listed earliest in the init.ora file. What if the rollback segments are created PUBLIC, and are not listed in init.ora? Order of sys.undo$.us#? Jared Cary Millsap [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/26/2002 11:15 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:RE: How are rollback segments assigned? Exactly. A guy might have to poll V$ROLLSTAT 100+ times per second to see the allocations happening on a system with well-designed transactions. You just can't do that with SQL. Raj, you *can* test the behavior by using some artificially *bad* transactions. On a quiescent system (nothing else running) with n rollback segments, open n+1 sqlplus sessions. In each session, update a row but don't commit. After each session's update, look at V$ROLLSTAT. To the best of my knowledge, the assignment algorithm has always been to assign a new txn to the segment with the smallest number of active txns in it. There are of course lots of ties (e.g., lots of segments might have 0 active txns in them). The tie-breaker in v6 was to assign in round-robin order (as the segments are listed in the init.ora file). In v7, the tie-breaker algorithm apparently changed to choose the segment that is listed earliest in the init.ora file. I don't know whether it changed again in 8 or 9. You'll know if you do the test. Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - Hotsos Clinic, Dec 9-11 Honolulu - Hotsos Clinic 101, Jan 7-9 Knoxville - Steve Adams's Miracle Master Class, Jan 13-15 Copenhagen - 2003 Hotsos Symposium, Feb 9-12 Dallas -Original Message- [EMAIL PROTECTED] Sent: Tuesday, November 26, 2002 12:25 PM To: Multiple recipients of list ORACLE-L Raj, You're assuming that the transactions are lasting long enough for you to catch them in the rollback segments. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/26/2002 09:42 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:Re: How are rollback segments assigned? Thanks Jared, thats not what I see. I have 20 rollback segments, and at no point in time, there were more than 4 transactions in the rollback segments. In fact, I happened to see it a couple of minutes ago. select usn, xacts from v$rollstat showed me 0 in 19 rollback segments, and 2 in one of them. And I have got alerts in place to alert me when there are more than 4 transactions in all of the rollback segments. And yeah, the rollback segments are online. Remains a mystery to me. Raj Jared.Still@r adisys.com To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] Sent by: cc: root@fatcity.Subject: Re: How are rollback segments assigned? com November 25, 2002 08:59 PM Please respond to ORACLE-L Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services
How are rollback segments assigned?
Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
Re: How are rollback segments assigned?
Here's one scenario: 4 transactions, 2 rollback segs tx 1 - rbs1 tx 2 - rbs 2 tx 3 - rbs 1 tx 4 - rbs 2 tx1 and tx3 finish. tx2 and tx4 have not yet committed. Jared [EMAIL PROTECTED] Sent by: [EMAIL PROTECTED] 11/25/2002 07:39 AM Please respond to ORACLE-L To: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] cc: Subject:How are rollback segments assigned? Hello Friends, Oracle Parallel Server 8.0.6.2.0 on Solaris 2.6 Nodes We were having some locking and rollback issues, and I set up some scripts to alert me in case there are more than 4 transactions in the rollback segments, and more than 1 in any of the rollback segments. Select sum(xacts) from v$rollstat --- Alert if more than 4, condition set to exclude system rollback where usn != 0 Select count(*) from v$rollstat --- Alert if more than 0, where condition to exclude system rollback where xacts =2 andusn != 0 We have 20 rollback segments, and there is very minimal DML activity on this database. I happened to see a scenario where all rollback segments had 0 transactions, except for one which had 2 in them. Under what scenario, can this happen? I thought the criteria for assigning rollback segments to transactions was 1. If object in system tablespace, use system rolback segment 2. Use the one with the least number of active transactions 3. If 2 or more rollback segments fit the second criteria, use the LRU algorithm. Thanks Raj -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
