How does the Capture process handle the situation where it is reading an online redo log which the Archiver process of Oracle (also termed as ARCH) is archiving.
Oracle writes to online redo logs in cyclical manner and it only overwrites one of the online redo logs if it is already archived. The Archiver process (also termed ARCH) copies online REDO LOG files to a designated storage device once it has become full and then overwrites it. The sequence of events is very quick. If the Capture process was already reading the online redo log to gather the changes when Oracle started archiving it, then the OS will ensure that though the redo log may be overwritten once the archiving is done, its read consistent image is still available for Capture to complete its task of reading. If the redo log is already archived by the time the Capture is in a position to read it, then Capture will be smart enough to look for it in the archive destination (usually pointed to by LOG_ARCHIVE_DEST).