Xref: alice comp.databases.oracle.server:26507 Path: alice!news-feed.fnsi.net!news.maxwell.syr.edu!woodstock.news.demon.net!demon!news.demon.nl!demon!sybrandb.demon.nl!not-for-mail From: Sybrand Bakker Newsgroups: comp.databases.oracle.server Subject: Re: Redo logs and rollback segments difference ? Date: Sat, 08 Aug 1998 11:40:58 +0200 Message-ID: <35CC1D29.839A2A1D@sybrandb.demon.nl> References: <35C03AF3.2050@platinum.com> X-Trace: news.demon.nl 902569364 rover:12951 NO-IDENT sybrandb.demon.nl:212.238.21.78 X-Complaints-To: abuse@demon.net X-Mailer: Mozilla 4.05 [en] (Win95; I) MIME-Version: 1.0 To: Jean-Francois Vincent Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 27 Rollback data contains the before image, the data before any changes, redo log contains the after image, the changed data. Henc, In recovery the redo log is used for roll forward and the rollback segments (which are also protected by redo log, any change is logged there) for rollback. In fact, writing the update,insert,delete changed data to the redo log is the first what is being done. Oracle assumes there are hotspots in the database, who are changed by more than one process. Transactions are piggybacked, until (usually 8) blocks in the cache are dirty. If you have 8 dirty blocks they are being written to the database files. This can be done because the changes have already been written to the redo log file. Hth Sybrand Bakker (postbus@sybrandb.demon.nl) Jean-Francois Vincent wrote: > Hello, i wonder what is the conceptual difference beetween redo log and > rollback segments under ORACLE. It seems the both contains transactions > bring possibility to rollback transaction, i guess transaction are > written twice in rollback and in redo log. Am i right ? > Can you explain me in detail the difference of each one ? > thank you very much. > > J-Fr.