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If you are acquiring the software on behalf of the Department of Defense, the software shall be classified as "Commercial Computer Software" and the Government shall have only "Restricted Rights" as defined in Clause 252.227-7013 (c) (1) of DFARs. Notwithstanding the foregoing, the authors grant the U.S. Government and others acting in its behalf permission to use and distribute the software in accordance with the terms specified in this license. ---*/ /** * @file * Manages the page buffer pageManager - Provides cached page handling, delegates to blob manager when necessary. Doesn't implement an eviction policy. That is left to a cacheManager. (Multiple cacheManagers can be used with a single page manager.) @todo Allow error checking! @todo Make linux provide a better version of malloc(). We need to directly DMA pages into and out of userland, or setup mmap() so that it takes a flag that makes it page mmapped() pages to swap instead of back to disk. (munmap() and msync() would still hit the on-disk copy) @todo Refactoring for lock manager Possible interface for lockManager: Define three classes of objects that the lock manager is interested in: Transactions, Operations, Predicates. LLADD already has operations and transactions, and these can be relatively unchanged. Predicates are read only operations that return a set of tuples. Tread() is the simplest predicate. Index scans provide a motivating example. See http://research.microsoft.com/%7Eadya/pubs/icde00.pdf (Generalized Isolation Level Definitions, Adya, Liskov, O'Neil, 2000) for a theoretical discussion of general locking schemes.. Locking functions can return errors such as DEADLOCK, etc. When such a value is returned, the transaction aborts, and an error is passed up to the application. * @ingroup LLADD_CORE * $Id$ */ #ifndef __BUFFERMANAGER_H__ #define __BUFFERMANAGER_H__ #include #include /** * initialize buffer manager * @return 0 on success * @return error code on failure */ int bufInit(); /** * @param pageid ID of the page you want to load * @return fully formed Page type * @return page with -1 ID if page not found */ Page loadPage(int pageid); /** * allocate a record * @param xid The active transaction. * @param size The size of the new record * @return allocated record */ recordid ralloc(int xid, long size); /** * Find a page with some free space. * */ /* * * This function updates the LSN of a page. * * This is needed by the * recovery process to make sure that each action is undone or redone * exactly once. * * @ param LSN The new LSN of the page. * @ param pageid ID of the page you want to write * * @ todo This needs to be handled by ralloc and writeRecord for * correctness. Right now, there is no way to atomically update a * page(!) To fix this, we need to change bufferManager's * implementation to use read/write (to prevent the OS from stealing * pages in the middle of updates), and alter kickPage to see what the * last LSN synced to disk was. If the log is too far behind, it will * need to either choose a different page, or call flushLog(). We may * need to implement a special version of fwrite() to do this * atomically. (write does not have to write all of the data that was * passed to it...) */ /*void writeLSN(long LSN, int pageid); */ /** * @param pageid ID of page you want to read * @return LSN found on disk */ long readLSN(int pageid); /** * @param xid transaction id * @param rid recordid where you want to write * @param dat data you wish to write */ void writeRecord(int xid, lsn_t lsn, recordid rid, const void *dat); /** * @param xid transaction ID * @param rid * @param dat buffer for data */ void readRecord(int xid, recordid rid, void *dat); /** * Write page to disk, including correct LSN. Doing so may require a * call to logSync(). There is not much that can be done to avoid * this call right now. In the future, it might make sense to check * to see if some other page can be kicked, in order to avoid the log * flush. * * @param page The page to be flushed to disk. */ void pageWrite(const Page * dat); /** Read a page from disk. @param A page struct, with id set correctly. The rest of this struct is filled out by pageMap. */ void pageRead(Page * ret); /* int flushPage(Page page); */ /*void pageMap(Page * page); */ /* * this function does NOT write to disk, just drops the page from the active * pages * @param page to take out of buffer manager * @return 0 on success * @return error code on failure int dropPage(Page page); */ /** * all actions necessary when committing a transaction. Can assume that the log * has been written as well as any other actions that do not depend on the * buffer manager * * Basicly, this call is here because we used to do copy on write, and * it might be useful when locking is implemented. * * @param xid transaction ID * @return 0 on success * @return error code on failure */ int bufTransCommit(int xid, lsn_t lsn); /** * * Currently identical to bufTransCommit. * * @param xid transaction ID * @return 0 on success * @return error code on failure */ int bufTransAbort(int xid, lsn_t lsn); /** * will write out any dirty pages, assumes that there are no running * transactions */ void bufDeinit(); /** @todo Global file descriptors are nasty. */ extern int blobfd0; extern int blobfd1; #endif