RE: Estimating space needed for UNDO tablespaces
Hi Jeff, Stealing extents is normal when there is no free space available to grow the active undo segment. If expired extents are getting stolen, I would not worry too much about adding more space to the undo tablespace, but monitor how much undo space the segment takes up. If unexpired extents are getting stolen, then you may have to consider either adding more space, or reducing undo retention time. If the undo tablespace does not have enough space to accommodate your largest transaction, event after stealing extents, and the data files are not autoexensible, then you will get ORA-1650 (I think, that the error#). And to avoid it, auto undo management still needs to be monitored! HTH, - Kirti --- Thomas Jeff [EMAIL PROTECTED] wrote: Kirti, Thanks for this information.I've implemented AUM in a number of our development databases.One of the things I have to do is write up a monitoring policy to hand to our contracted production DBAs -- guidelines on how to address certain scenarios and so forth -- otherwise, they will simply resort to adding 'more' of whatever they presume is in short supply in event of a production crisis. For example, I'm seeing some steal counts in v$undostat, implying that the undo tablespace needs more space. However, from what you are saying, it seems that if undo_retention is consistently larger then maxquerylen during the period of time when the steal counts occur, that maybe the smarter thing to do is simply reduce the undo_retention parameter before considering adding more space? Jeff -Original Message- Sent: Friday, September 26, 2003 11:50 PM To: Multiple recipients of list ORACLE-L You can run following query to get an idea of undo generation rate and max query length: SELECT to_char(min(begin_time),'MM/DD/ HH24:MI:SS') Begin Time, to_char(max(end_time),'MM/DD/ HH24:MI:SS') End Time, (max(end_time)-min(begin_time))*24*60*60 Seconds, sum(undoblks) UndoBlks, sum(undoblks)/((max(end_time)-min(begin_time))*24*60*60) UndoBlksPerSec, max(maxquerylen) MaxQueryLenSecs FROM v$undostat; Unfortunately, the TXNCOUNT column in v$undostat view in Oracle 9.2.0.x is screwed up. It does not correctly report the transaction count for the sample interval. Instead it keeps accumulating. One needs to do the math to get the correct count for the desired sample interval. It will show the time of high transaction activity with related undo generation. Oracle recommends setting undo_retention to the max(maxquerylen), but use your judgement. If data loads and queries accessing same tables, do not run at the same time (in DW, for example), setting undo_retention to a high number (maxquerylen) will simply waste disk space. If undo_retention is not set appropriately, you will get ORA-1555, and it will be reported in alert.log along with the affected SQL statement. The log entry will also contain the query time, in seconds, before it got aborted due to ORA-1555. Also, the above query works only when the database is using AUM. V$undostat does not report anything in 9.2.0.x when using MUM (manual undo mode). In 9.0.1, it returns one useless row when using MUM! BTW, you can also use the OEM to see the undo generation rate. It is one of the few things in OEM (standalone mode) I use. Hth. - Kirti snip __ Do you Yahoo!? The New Yahoo! Shopping - with improved product search http://shopping.yahoo.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Kirtikumar Deshpande 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: Estimating space needed for UNDO tablespaces
Try these queries. /* Rows returned below mean that UNDO_RETENTION needs to be increased */ select * from v$undostat where UNXPSTEALCNT 0 or SSOLDERRCNT 0; /* Rows returned below mean that space needs to be added to the undo tablespace. All space in the tablespace was used and no free space was available when requested */ select * from v$undostat where NOSPACEERRCNT 0; Kirtikumar DeshpandeTo: Multiple recipients of list ORACLE-L [EMAIL PROTECTED] kirtikumar_desh cc: pandeSubject: RE: Estimating space needed for UNDO tablespaces @yahoo.com Sent by: ml-errors 10/01/2003 10:14 AM Please respond to ORACLE-L Hi Jeff, Stealing extents is normal when there is no free space available to grow the active undo segment. If expired extents are getting stolen, I would not worry too much about adding more space to the undo tablespace, but monitor how much undo space the segment takes up. If unexpired extents are getting stolen, then you may have to consider either adding more space, or reducing undo retention time. If the undo tablespace does not have enough space to accommodate your largest transaction, event after stealing extents, and the data files are not autoexensible, then you will get ORA-1650 (I think, that the error#). And to avoid it, auto undo management still needs to be monitored! HTH, - Kirti --- Thomas Jeff [EMAIL PROTECTED] wrote: Kirti, Thanks for this information.I've implemented AUM in a number of our development databases.One of the things I have to do is write up a monitoring policy to hand to our contracted production DBAs -- guidelines on how to address certain scenarios and so forth -- otherwise, they will simply resort to adding 'more' of whatever they presume is in short supply in event of a production crisis. For example, I'm seeing some steal counts in v$undostat, implying that the undo tablespace needs more space. However, from what you are saying, it seems that if undo_retention is consistently larger then maxquerylen during the period of time when the steal counts occur, that maybe the smarter thing to do is simply reduce the undo_retention parameter before considering adding more space? Jeff -Original Message- Sent: Friday, September 26, 2003 11:50 PM To: Multiple recipients of list ORACLE-L You can run following query to get an idea of undo generation rate and max query length: SELECT to_char(min(begin_time),'MM/DD/ HH24:MI:SS') Begin Time, to_char(max(end_time),'MM/DD/ HH24:MI:SS') End Time, (max(end_time)-min(begin_time))*24*60*60 Seconds, sum(undoblks) UndoBlks, sum(undoblks)/((max(end_time)-min(begin_time))*24*60*60) UndoBlksPerSec, max(maxquerylen) MaxQueryLenSecs FROM v$undostat; Unfortunately, the TXNCOUNT column in v$undostat view in Oracle 9.2.0.x is screwed up. It does not correctly report the transaction count for the sample interval. Instead it keeps accumulating. One needs to do the math to get the correct count for the desired
RE: Estimating space needed for UNDO tablespaces
Kirti, Thanks for this information.I've implemented AUM in a number of our development databases.One of the things I have to do is write up a monitoring policy to hand to our contracted production DBAs -- guidelines on how to address certain scenarios and so forth -- otherwise, they will simply resort to adding 'more' of whatever they presume is in short supply in event of a production crisis. For example, I'm seeing some steal counts in v$undostat, implying that the undo tablespace needs more space. However, from what you are saying, it seems that if undo_retention is consistently larger then maxquerylen during the period of time when the steal counts occur, that maybe the smarter thing to do is simply reduce the undo_retention parameter before considering adding more space? Jeff -Original Message- Sent: Friday, September 26, 2003 11:50 PM To: Multiple recipients of list ORACLE-L You can run following query to get an idea of undo generation rate and max query length: SELECT to_char(min(begin_time),'MM/DD/ HH24:MI:SS') Begin Time, to_char(max(end_time),'MM/DD/ HH24:MI:SS') End Time, (max(end_time)-min(begin_time))*24*60*60 Seconds, sum(undoblks) UndoBlks, sum(undoblks)/((max(end_time)-min(begin_time))*24*60*60) UndoBlksPerSec, max(maxquerylen) MaxQueryLenSecs FROM v$undostat; Unfortunately, the TXNCOUNT column in v$undostat view in Oracle 9.2.0.x is screwed up. It does not correctly report the transaction count for the sample interval. Instead it keeps accumulating. One needs to do the math to get the correct count for the desired sample interval. It will show the time of high transaction activity with related undo generation. Oracle recommends setting undo_retention to the max(maxquerylen), but use your judgement. If data loads and queries accessing same tables, do not run at the same time (in DW, for example), setting undo_retention to a high number (maxquerylen) will simply waste disk space. If undo_retention is not set appropriately, you will get ORA-1555, and it will be reported in alert.log along with the affected SQL statement. The log entry will also contain the query time, in seconds, before it got aborted due to ORA-1555. Also, the above query works only when the database is using AUM. V$undostat does not report anything in 9.2.0.x when using MUM (manual undo mode). In 9.0.1, it returns one useless row when using MUM! BTW, you can also use the OEM to see the undo generation rate. It is one of the few things in OEM (standalone mode) I use. Hth. - Kirti --- Daniel Fink [EMAIL PROTECTED] wrote: That sounds very reasonable. You can check that number against the values in v$undostat as it runs. Remember, UNDO_RETENTION is not guaranteed. If the space is needed by another segment, it may be taken even if the expire time has not been reached. Daniel Thomas Jeff wrote: Thanks for the reply Dan. Would you suggest setting UNDO_RETENTION to roughly the length of time of the longest running job in the database? For example, in our DW, our BI analysts tell me that their longest batch run is about 1 hr 45 minutes. My uneducated guess is to accordingly set the parameter to approx 2 hours. -Original Message- Sent: Friday, September 26, 2003 4:15 PM To: Multiple recipients of list ORACLE-L That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work. Daniel Fink Thomas Jeff wrote: I'm beginning the process of converting over to automatic undo management. I'm wondering as to exactly how large to initially build the UNDO tablespace.Make it roughly the same size as the sum of the current rollback tablespaces?Or has your experience been different, i.e., you've found you've generally needed more or less space with respect to the previous allocation for rollback segments (manual undo)? Thanks. Jeffery D Thomas DBA Thomson Information Services Thomson, Inc. __ Do you Yahoo!? The New Yahoo! Shopping - with improved product search http://shopping.yahoo.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Kirtikumar Deshpande INET: [EMAIL PROTECTED] Fat City Network Services-- 858-538-5051 http://www.fatcity.com San Diego, California-- Mailing list and web hosting services - To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of
Re: Estimating space needed for UNDO tablespaces
That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work. Daniel Fink Thomas Jeff wrote: I'm beginning the process of converting over to automatic undo management. I'm wondering as to exactly how large to initially build the UNDO tablespace.Make it roughly the same size as the sum of the current rollback tablespaces?Or has your experience been different, i.e., you've found you've generally needed more or less space with respect to the previous allocation for rollback segments (manual undo)? Thanks. Jeffery D Thomas DBA Thomson Information Services Thomson, Inc. Email: [EMAIL PROTECTED] Indy DBA Master Documentation available at: http://gkmqp.tce.com/tis_dba -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Thomas Jeff 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). begin:vcard n:Fink;Daniel x-mozilla-html:FALSE org:Sun Microsystems, Inc. adr:;; version:2.1 title:Lead, Database Services x-mozilla-cpt:;9168 fn:Daniel W. Fink end:vcard
RE: Estimating space needed for UNDO tablespaces
Thanks for the reply Dan. Would you suggest setting UNDO_RETENTION to roughly the length of time of the longest running job in the database? For example, in our DW, our BI analysts tell me that their longest batch run is about 1 hr 45 minutes. My uneducated guess is to accordingly set the parameter to approx 2 hours. -Original Message- Sent: Friday, September 26, 2003 4:15 PM To: Multiple recipients of list ORACLE-L That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work. Daniel Fink Thomas Jeff wrote: I'm beginning the process of converting over to automatic undo management. I'm wondering as to exactly how large to initially build the UNDO tablespace.Make it roughly the same size as the sum of the current rollback tablespaces?Or has your experience been different, i.e., you've found you've generally needed more or less space with respect to the previous allocation for rollback segments (manual undo)? Thanks. Jeffery D Thomas DBA Thomson Information Services Thomson, Inc. Email: [EMAIL PROTECTED] Indy DBA Master Documentation available at: http://gkmqp.tce.com/tis_dba -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Thomas Jeff 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.net -- Author: Thomas Jeff 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: Estimating space needed for UNDO tablespaces
That sounds very reasonable. You can check that number against the values in v$undostat as it runs. Remember, UNDO_RETENTION is not guaranteed. If the space is needed by another segment, it may be taken even if the expire time has not been reached. Daniel Thomas Jeff wrote: Thanks for the reply Dan. Would you suggest setting UNDO_RETENTION to roughly the length of time of the longest running job in the database? For example, in our DW, our BI analysts tell me that their longest batch run is about 1 hr 45 minutes. My uneducated guess is to accordingly set the parameter to approx 2 hours. -Original Message- Sent: Friday, September 26, 2003 4:15 PM To: Multiple recipients of list ORACLE-L That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work. Daniel Fink Thomas Jeff wrote: I'm beginning the process of converting over to automatic undo management. I'm wondering as to exactly how large to initially build the UNDO tablespace.Make it roughly the same size as the sum of the current rollback tablespaces?Or has your experience been different, i.e., you've found you've generally needed more or less space with respect to the previous allocation for rollback segments (manual undo)? Thanks. Jeffery D Thomas DBA Thomson Information Services Thomson, Inc. Email: [EMAIL PROTECTED] Indy DBA Master Documentation available at: http://gkmqp.tce.com/tis_dba -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Thomas Jeff 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.net -- Author: Thomas Jeff 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). begin:vcard n:Fink;Daniel x-mozilla-html:FALSE org:Sun Microsystems, Inc. adr:;; version:2.1 title:Lead, Database Services x-mozilla-cpt:;9168 fn:Daniel W. Fink end:vcard
Re: Estimating space needed for UNDO tablespaces
You can run following query to get an idea of undo generation rate and max query length: SELECT to_char(min(begin_time),'MM/DD/ HH24:MI:SS') Begin Time, to_char(max(end_time),'MM/DD/ HH24:MI:SS') End Time, (max(end_time)-min(begin_time))*24*60*60 Seconds, sum(undoblks) UndoBlks, sum(undoblks)/((max(end_time)-min(begin_time))*24*60*60) UndoBlksPerSec, max(maxquerylen) MaxQueryLenSecs FROM v$undostat; Unfortunately, the TXNCOUNT column in v$undostat view in Oracle 9.2.0.x is screwed up. It does not correctly report the transaction count for the sample interval. Instead it keeps accumulating. One needs to do the math to get the correct count for the desired sample interval. It will show the time of high transaction activity with related undo generation. Oracle recommends setting undo_retention to the max(maxquerylen), but use your judgement. If data loads and queries accessing same tables, do not run at the same time (in DW, for example), setting undo_retention to a high number (maxquerylen) will simply waste disk space. If undo_retention is not set appropriately, you will get ORA-1555, and it will be reported in alert.log along with the affected SQL statement. The log entry will also contain the query time, in seconds, before it got aborted due to ORA-1555. Also, the above query works only when the database is using AUM. V$undostat does not report anything in 9.2.0.x when using MUM (manual undo mode). In 9.0.1, it returns one useless row when using MUM! BTW, you can also use the OEM to see the undo generation rate. It is one of the few things in OEM (standalone mode) I use. Hth. - Kirti --- Daniel Fink [EMAIL PROTECTED] wrote: That sounds very reasonable. You can check that number against the values in v$undostat as it runs. Remember, UNDO_RETENTION is not guaranteed. If the space is needed by another segment, it may be taken even if the expire time has not been reached. Daniel Thomas Jeff wrote: Thanks for the reply Dan. Would you suggest setting UNDO_RETENTION to roughly the length of time of the longest running job in the database? For example, in our DW, our BI analysts tell me that their longest batch run is about 1 hr 45 minutes. My uneducated guess is to accordingly set the parameter to approx 2 hours. -Original Message- Sent: Friday, September 26, 2003 4:15 PM To: Multiple recipients of list ORACLE-L That is a good place to start. You might consider adding a little if you have many concurrent transactions or want to increase the undo_retention to a high number. Once you are using AUM, keep a close eye on v$undostat, though there are some known issues with it not populating properly, keep an eye on the begin_time and end_time. However, for estimation purposes it should work. Daniel Fink Thomas Jeff wrote: I'm beginning the process of converting over to automatic undo management. I'm wondering as to exactly how large to initially build the UNDO tablespace.Make it roughly the same size as the sum of the current rollback tablespaces?Or has your experience been different, i.e., you've found you've generally needed more or less space with respect to the previous allocation for rollback segments (manual undo)? Thanks. Jeffery D Thomas DBA Thomson Information Services Thomson, Inc. __ Do you Yahoo!? The New Yahoo! Shopping - with improved product search http://shopping.yahoo.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Kirtikumar Deshpande 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).
