Xref: alice comp.databases.oracle.server:26522 Path: alice!news-feed.fnsi.net!newsfeed.direct.ca!news-peer.sprintlink.net!news-peer-east.sprintlink.net!news.sprintlink.net!ix.netcom.com!news From: "Winnie Liu" Newsgroups: comp.databases.oracle.server Subject: Re: Redo logs and rollback segments difference ? Date: Sat, 8 Aug 1998 08:59:07 -0700 Organization: ICGNetcom Lines: 49 Message-ID: <6qhsc2$ivu@sjx-ixn11.ix.netcom.com> References: <35C03AF3.2050@platinum.com> <35CC1D29.839A2A1D@sybrandb.demon.nl> <6qho0l$gfe$1@news-1.news.gte.net> X-NETCOM-Date: Sat Aug 08 8:54:42 AM PDT 1998 X-Newsreader: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 The redo log contains before and after images. As for the rollback segment, it depends, if it is a pure insert on the table, it will contain the rowid of the rows that are being inserted without commit; if it is a delete on the table, it will contain all the information of the deleted rows. if it is a update, it will contain the before and after images of the columns that are being updated. Winnie johnvue@gte.net wrote in message <6qho0l$gfe$1@news-1.news.gte.net>... >Just for your info, more than one book states that rollback data first >has to go through redo buffer which of course goes through the redo >logs. So the redo logs contain BOTH before and after images. You are >correct in saying Oracle doesn't USE the redo logs for rolling back. > >On Sat, 08 Aug 1998 11:40:58 +0200, in comp.databases.oracle.server >you wrote: > >>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. >> >> >