In this case, the situation is more complicated. It's an Oracle 10.2.0.1 database running in Linux. The database was shutdown abnormally; There are only 3 data files can be used, 2 of them are system files, whose file IDs are not in sequence; the other one is the data file contain the data to be rescued. The control files, redo logs, undo files, temp files and other data files are lost. During this process, I encoutered more problems, but I work it out finally.
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To guarantee the safety of our data, we need to prepare a good backup/restore plan as well as Disaster Recovery solutions. However, for some reasons, many database systems are not maintained very well, and may encounter some fatal issues, e.g. Control files and Online REDO log fils are lost. In such situation, we need use some un-normal methods, such as hidden parameters, BBED and even Dul, to rescue the data. Now, my question is that, what is the worst situation having hope to rescue data. Theoretically, the data is comprised 2 important parts, data definition (also known as meta data) and data records. The data records are stored in the user data files, and the meta data is stored in system data files. Let's say, if there are only system files and key user data files (not all of data files) are un-corrupted, is it possible to rescue the data? Of course, we are not discussing using Dul to rescue the data.
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Buffer Cache is an important part of Oracle memory, it caches the data block read from data files. Hence, it impacts the performance very much. To improve performance using this limited resource, Oracle adopts LRU algorithm to manage the buffer block allocation and deallocation. LRU algorithm is quite familiar to us, because it has been explained in Oracle online document and other books very well. However, it's not easy to identify the postion of a buffer block in the buffer chain (although we can use oradebug to print a buffer chain to a trace file, it's little bit complicated and hard to read). In this book, I created the view v_bufheaders to show the position in the buffer chain and other information of the buffer block.
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Erratum of "Oracle SQL Optimizing and Tuning Technologies"
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To descript and demonstrate the usage of Oracle SQL Hints.
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Scripts of "Oracle SQL Optimizing and Tuning Technologies"
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