RE: Sequences in OPS/RAC
Hemant, I would guess that this is true if you are caching values for the sequence. Each database instance might cache the same set of values. Turn sequence caching off, and I would think that the problem goes away. Havn't tried this in awhile, but it makes sense. Tom Mercadante Oracle Certified Professional -Original Message- Sent: Monday, November 03, 2003 10:39 AM To: Multiple recipients of list ORACLE-L I have always been comfortable with the idea that Sequences continue to guarantee uniqueness even in OPS / RAC environments. However, a recent Builder.Com article by Scott Stephens on the SYS_GUID function has these lines : Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts. An identifier created by SYS_GUID is guaranteed to be unique for each database. Huh ?! Do the lines mean that a single sequence can have duplicate values in the two instances of an RAC cluster ? Hemant K Chitale Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale 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: Mercadante, Thomas F 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: Sequences in OPS/RAC
me don't think so. Raj Rajendra dot Jamadagni at nospamespn dot com All Views expressed in this email are strictly personal. QOTD: Any clod can have facts, having an opinion is an art ! -Original Message- Sent: Monday, November 03, 2003 10:39 AM To: Multiple recipients of list ORACLE-L I have always been comfortable with the idea that Sequences continue to guarantee uniqueness even in OPS / RAC environments. However, a recent Builder.Com article by Scott Stephens on the SYS_GUID function has these lines : Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts. An identifier created by SYS_GUID is guaranteed to be unique for each database. Huh ?! Do the lines mean that a single sequence can have duplicate values in the two instances of an RAC cluster ? Hemant K Chitale Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale 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). ** This e-mail message is confidential, intended only for the named recipient(s) above and may contain information that is privileged, attorney work product or exempt from disclosure under applicable law. If you have received this message in error, or are not the named recipient(s), please immediately notify corporate MIS at (860) 766-2000 and delete this e-mail message from your computer, Thank you. **4 -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Jamadagni, Rajendra 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: Sequences in OPS/RAC
In the Oracle9i Real Application Clusters Administration manual, there is a chapter about sequence numbers generator. Before believing to the snake oil sellers, read the fine manual. Sequence numbers are guaranteed to be unique PER DATABASE. What they're not guaranteed is to come in ordered fashion. When sequence number are cached (that is the default), they're cached separately, for each instance. Each instance returns the contents of its cache, so it is possible for the smaller number being returned after a larger one. There is ORDERED flag to deal with that, but that can be extremely expensive and impose significant overhead on your cluster. On 11/03/2003 10:39:26 AM, Hemant K Chitale wrote: I have always been comfortable with the idea that Sequences continue to guarantee uniqueness even in OPS / RAC environments. However, a recent Builder.Com article by Scott Stephens on the SYS_GUID function has these lines : Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts. An identifier created by SYS_GUID is guaranteed to be unique for each database. Huh ?! Do the lines mean that a single sequence can have duplicate values in the two instances of an RAC cluster ? Hemant K Chitale Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale 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). Mladen Gogala Oracle DBA Note: This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. Wang Trading LLC and any of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorized to state them to be the views of any such entity. -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Mladen Gogala 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: Sequences in OPS/RAC
Sequences are mastered by the single SYS.SEQ$ table in each database. Cached or uncached, RAC or non-RAC, OPS or non-OPS, sequence numbers generated by this mechanism are unique across a database, not by instance. Each instance updates SEQ$ as individual numbers (noncached) or ranges of numbers (cached) are reserved, and those updates are controlled by the same synchronization mechanisms used by OPS/RAC for all UPDATE statements. This is precisely the reason that setting CACHE on sequence numbers help performance, as the number of updates to SEQ$ are reduced, minimizing the bottleneck. However, because of the simplicity of this caching mechanism, sequence numbers are not guaranteed to be in order (i.e. sequentially ascending) across multiple instances. Perhaps Mr. Stephens mis-spoke, confusing uniqueness for ordering? Or perhaps he is confusing distributed databases for clustered databases? I have always been comfortable with the idea that Sequences continue to guarantee uniqueness even in OPS / RAC environments. However, a recent Builder.Com article by Scott Stephens on the SYS_GUID function has these lines : Sequence generator numbers are guaranteed to be unique only for a single instance, which is unsuitable for use as a primary key in parallel or remote environments, where a sequence in each environment might generate the same number and result in conflicts. An identifier created by SYS_GUID is guaranteed to be unique for each database. Huh ?! Do the lines mean that a single sequence can have duplicate values in the two instances of an RAC cluster ? Hemant K Chitale Oracle 9i Database Administrator Certified Professional My personal web site is : http://hkchital.tripod.com -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Hemant K Chitale 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: Tim Gorman 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: Sequences in OPS/RAC
Yes, I've been aware of the difference between ORDERED and CACHED.
However, the Builder.Com article quite explicity asserts
Sequence generator numbers are guaranteed to be unique only for a single
instance, which is unsuitable for use as a primary key in parallel or
remote environments, where a sequence in each environment might generate
the same number and result in conflicts
Sequence generator numbers are guaranteed to be unique only for a single
instance, which is unsuitable for use as a primary key in parallel or
remote environments, where a sequence in each environment might generate
the same number and result in conflicts
As Tim has pointed out earlier, the author of the article might have confused
uniqueness with ordering.
{I've sent copies of the builder.com article by seperate emails to Raj and Tim}
Hemant
At 07:59 AM 03-11-03 -0800, you wrote:
In the Oracle9i Real Application Clusters Administration manual, there
is a chapter
about sequence numbers generator. Before believing to the snake oil
sellers, read
the fine manual. Sequence numbers are guaranteed to be unique PER
DATABASE. What they're
not guaranteed is to come in ordered fashion. When sequence number are
cached (that is the
default), they're cached separately, for each instance. Each instance
returns the contents
of its cache, so it is possible for the smaller number being returned
after a larger one.
There is ORDERED flag to deal with that, but that can be extremely
expensive and impose
significant overhead on your cluster.
On 11/03/2003 10:39:26 AM, Hemant K Chitale wrote:
I have always been comfortable with the idea that Sequences continue to
guarantee
uniqueness even in OPS / RAC environments.
However, a recent Builder.Com article by Scott Stephens on the SYS_GUID
function has these lines :
Sequence generator numbers are guaranteed to be unique only for a single
instance, which is unsuitable for use as a primary key in parallel or
remote environments, where a sequence in each environment might generate
the same number and result in conflicts. An identifier created by SYS_GUID
is guaranteed to be unique for each database.
Huh ?! Do the lines mean that a single sequence can have duplicate values
in the two instances of an RAC cluster ?
Hemant K Chitale
Oracle 9i Database Administrator Certified Professional
My personal web site is : http://hkchital.tripod.com
--
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Mladen Gogala
Oracle DBA
Note:
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intended recipient. Wang Trading LLC and any of its subsidiaries each
reserve the right to monitor all e-mail communications through its networks.
Any views expressed in this message are those of the individual sender,
except where the message states otherwise and the sender is authorized to
state them to be the views of any such entity.
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My personal web site is : http://hkchital.tripod.com
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
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Author: Hemant K Chitale
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