HDR Secondary mode Log transfer handling
A user asked how Informix HDR works: whether changes on the primary keep flowing to the read-only secondary, whether they are applied there, how locking is handled, and at what granularity logs are shipped. Answers: yes to both — anything logically logged replicates (non-logged tables and blobspace blobs do not), queries on the secondary run at dirty read isolation, and data is sent per logical-log buffer as it is flushed to disk, not per full log file. Advice given: use UNBUFFERED logging to protect secondary integrity, and note that if the primary wraps a log the secondary still needs, HDR must be rebuilt from scratch.
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In the HDR configuration of Informix database, the Backup database is running in "Secondary" mode and in read only access status. 1) Does the updates on Primary database server keep on transferring to Backup database? 2) Is the updates from the Primary database applied to the "read only" Backup database?
1) Does the updates on Primary database server keep on transferring to Backup database? Yes, whatever gets logically logged. Not logically logged are e.g. tables in non-logged databases or blobspace blobs. 2) Is the updates from the Primary database applied to the "read only" Backup database? Yes. IBM Deutschland GmbH / Chairman of the Supervisory Board: Hans Ulrich Maerki Board of Management: Martin Jetter (Chairman), Rudolf Bauer, Christian Diedrich, Christoph Grandpierre, Matthias Hartmann, Thomas Fell, Michael Diemer Corporate Seat: Stuttgart / Reg.-Gericht: Amtsgericht Stuttgart, HRB 14562 / WEEE-Reg.-Nr. DE 99369940 "DANNY NG" <nd504@ha.org.hk> Sent by: To ids-bounces@iiug. ids@iiug.org org cc Subject 08/28/07 11:17 AM HDR Secondary mode Log transfer handling [9866] Please respond to ids@iiug.org In the HDR configuration of Informix database, the Backup database is running in "Secondary" mode and in read only access status. 1) Does the updates on Primary database server keep on transferring to Backup database? 2) Is the updates from the Primary database applied to the "read only" Backup database? ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.
How the Informix handle the locking between the read only access and updates from Primary Database to Backup database?
How the Informix handle the locking between the read only access and updates from Primary Database to Backup database? Queries on HDR secondary are running in dirty read isolation level. IBM Deutschland GmbH / Chairman of the Supervisory Board: Hans Ulrich Maerki Board of Management: Martin Jetter (Chairman), Rudolf Bauer, Christian Diedrich, Christoph Grandpierre, Matthias Hartmann, Thomas Fell, Michael Diemer Corporate Seat: Stuttgart / Reg.-Gericht: Amtsgericht Stuttgart, HRB 14562 / WEEE-Reg.-Nr. DE 99369940 "DANNY NG" <nd504@ha.org.hk> Sent by: To ids-bounces@iiug. ids@iiug.org org cc Subject 08/28/07 11:37 AM Re: HDR Secondary mode Log transfer handling [9868] Please respond to ids@iiug.org How the Informix handle the locking between the read only access and updates from Primary Database to Backup database? ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.
Hi, 1) yes. 2) yes. This is the purpose of Informix HDR (High availability Data Replication). As long as the network connection is working, the IDS Primary and Secondary servers will stay connected and exchange information continuously. Any changes on the Primary server will be replicated to the Secondary server and applied there. Short, transient interruptions of the network connection between the two servers are acceptable as long as it is possible for the servers to reconnect before the Secondary server falls behind too much. The Secondary server definitely fell behind too much when the Primary server has overwritten a logical log file (logical log wrap around) that the Secondary server would still need to apply on his side. This is kind of the "point of no return" - if it happens, then HDR must be setup again from scratch. Before that happens there's always the chance that Secondary server can catch up again with Primary server, possibly even after a longer connection interruption. It depends on how busy the Primary server is. Regards, Martin -- Martin Fuerderer IBM Informix Development Munich, Germany Information Management IBM Deutschland GmbH Chairman of the Supervisory Board: Hans Ulrich Märki Board of Management: Martin Jetter (Chairman), Rudolf Bauer, Christian Diedrich, Christoph Grandpierre, Matthias Hartmann, Thomas Fell, Michael Diemer Corporate Seat: Stuttgart, Germany; Reg.-Gericht: Amtsgericht Stuttgart, HRB-Nr.: 14 562 WEEE-Reg.-Nr. DE 99369940 ids-bounces@iiug.org wrote on 28.08.2007 11:17:50: > > In the HDR configuration of Informix database, the Backup database is running > in "Secondary" mode and in read only access status. > 1) Does the updates on Primary database server keep on transferring to Backup > database? > 2) Is the updates from the Primary database applied to the "read only" Backup > database? > > > ******************************************************************************* > Forum Note: Use "Reply" to post a response in the discussion forum.
How the transcation is delivered from Primary Database to Secondary Database? - In a full logical log ? - Any committed transaction at Primary Database? If the transaction is delivered from Priamry to Secondary Database in a full logical log, then any recommendation on the size of logical log in order to minimize data inconsistency between Primary and Secondary Database.
As each log buffer is flushed to disk, it is also transmitted to the secondary. = "DANNY NG" = <nd504@ha.org.hk> = Sent by: = To ids-bounces@iiug. ids@iiug.org = org = cc = Subj= ect 08/29/2007 08:45 Re: HDR Secondary mode Log trans= fer PM handling [9876] = = = Please respond to = ids@iiug.org = = = How the transcation is delivered from Primary Database to Secondary Database? - In a full logical log ? - Any committed transaction at Primary Database? If the transaction is delivered from Priamry to Secondary Database in a= full logical log, then any recommendation on the size of logical log in orde= r to minimize data inconsistency between Primary and Secondary Database. ***********************************************************************= ******** Forum Note: Use "Reply" to post a response in the discussion forum. =
Each logical log buffer is transmitted to the secondary at the time it is flushed to the current logical log on disk. That is why if you are using HDR it is critical for the integrity of the secondary that all databases use UNBUFFERED LOG mode logging to minimize the possibility of logical log buffers being lost before they are flushed to disk in the event of a hard crash. Art S. Kagel ----- Original Message ----- From: Danny Ng <ids@iiug.org> At: 8/29 21:46:24 How the transcation is delivered from Primary Database to Secondary Database? - In a full logical log ? - Any committed transaction at Primary Database? If the transaction is delivered from Priamry to Secondary Database in a full logical log, then any recommendation on the size of logical log in order to minimize data inconsistency between Primary and Secondary Database. ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.