274 lines
8.6 KiB
C
274 lines
8.6 KiB
C
/*---
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This software is copyrighted by the Regents of the University of
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California, and other parties. The following terms apply to all files
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associated with the software unless explicitly disclaimed in
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individual files.
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The authors hereby grant permission to use, copy, modify, distribute,
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and license this software and its documentation for any purpose,
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provided that existing copyright notices are retained in all copies
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and that this notice is included verbatim in any distributions. No
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written agreement, license, or royalty fee is required for any of the
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authorized uses. Modifications to this software may be copyrighted by
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their authors and need not follow the licensing terms described here,
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provided that the new terms are clearly indicated on the first page of
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each file where they apply.
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IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
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FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
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DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND
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NON-INFRINGEMENT. THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, AND
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THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
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MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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GOVERNMENT USE: If you are acquiring this software on behalf of the
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U.S. government, the Government shall have only "Restricted Rights" in
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the software and related documentation as defined in the Federal
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Acquisition Regulations (FARs) in Clause 52.227.19 (c) (2). If you are
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acquiring the software on behalf of the Department of Defense, the
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software shall be classified as "Commercial Computer Software" and the
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Government shall have only "Restricted Rights" as defined in Clause
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252.227-7013 (c) (1) of DFARs. Notwithstanding the foregoing, the
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authors grant the U.S. Government and others acting in its behalf
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permission to use and distribute the software in accordance with the
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terms specified in this license.
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---*/
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/**
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* @file
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* Manages the page buffer
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*
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* @todo Allow error checking!
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*
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* @todo CORRECTNESS PROBLEM: Recovery assumes that each page is
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* written atomically to disk, and that the LSN field of the page will
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* be in sync with the contents of each record on the page. Since we
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* use mmap() to read and write the pages, and a page fault could
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* interrupt LLADD between a writeRecord and writeLSN call, it is
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* possible for the operating system to steal dirty pages from the
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* buffer manager. (We support steal in the normal case, but still
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* need to be sure that the stolen pages are internally consistent!)
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*
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* It looks as though we will need to re-write the buffer manager so
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* that it only uses read or write calls. Alternatively, we could
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* lock pages as we update them, but that requires root privliges.
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*
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* @todo Refactoring for lock manager / correctness
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*
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* Possible interfaces:
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*
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pageManager - Provides cached page handling, delegates to blob
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manager when necessary. Doesn't implement an eviction policy.
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That is left to a cacheManager. (Multiple cacheManagers can be
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used with a single page manager.)
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typedef struct {
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Page * page;
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/ * If this page is pinned, what's the maximum lsn that's dirtied it? * /
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lsn_t * max_dirty_lsn = 0;
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/ * How many times has this page been pinned using readWriteMap()? * /
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int pin_count;
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} page_metadata_t;
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Calls for user managed memory:
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Read only access to record:
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Cost with cache hit: memcpy();
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- int readRecord(rid, void *);
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Write record directly:
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Cost with cache hit: memcpy(rid.size), eventual disk flush;
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- int writeRecord(rid, lsn, void *);
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@todo need alloc + free...
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// Calls for LLADD managed memory (returns pointers to LLADD's cache.)
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// Read only access to record (requires an un-pinning)
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// Cost with cache hit: pointer arithmetic.
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// - map_t readMapRecord(rid, &((const void *));
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// Map a page read / write. Pins the page, sets its lsn, and provides a pointer to the record:
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// Cost with cache hit: pointer arithmetic, eventual disk flush.
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// - map_t readWriteMapRecord(rid, &(void *));
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// Unmap a mapped page so that it can be kicked.
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// @param lsn can be 0 if this is a read-only mapping. Otherwise,
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// it should be the LSN of the operation that calls unmapRecord.
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// @todo What connection between the lock manager and this function
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// is there? Presumably, unmap should be called when the locks are
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// released...
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//
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// - void unmapRecord(map_t, lsn);
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cachePolicy
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page_id kickPage(); // Choose a page to kick. May call logFlush() if necessary.
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readPage(page); // Inform the cache that a page was read.
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writePage(page); // Inform the cache that a page was written.
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cacheHint(void *); // Optional method needed to implement dbmin.
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lockManager
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- These functions provide a locking implementation based on logical operations:
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lock_t lock(Operation o);
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unlock(Operation o);
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- These functions provide a locking implementation based on physical operations:
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(Insert bufferManager API here, but make each call take a xid and a lock_t* parameter)
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Locking functions can return errors such as DEADLOCK, etc.
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*
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* @ingroup LLADD_CORE
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* $Id$
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*/
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#ifndef __BUFFERMANAGER_H__
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#define __BUFFERMANAGER_H__
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#include <lladd/page.h>
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#include <lladd/constants.h>
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/**
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* initialize buffer manager
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* @return 0 on success
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* @return error code on failure
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*/
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int bufInit();
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/**
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* @param pageid ID of the page you want to load
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* @return fully formed Page type
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* @return page with -1 ID if page not found
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*/
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Page loadPage(int pageid);
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/**
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* allocate a record
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* @param xid The active transaction.
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* @param size The size of the new record
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* @return allocated record
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*/
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recordid ralloc(int xid, lsn_t lsn, size_t size);
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/**
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* Find a page with some free space.
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*
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*/
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/**
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* This function updates the LSN of a page.
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*
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* This is needed by the
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* recovery process to make sure that each action is undone or redone
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* exactly once.
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*
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* @param LSN The new LSN of the page.
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* @param pageid ID of the page you want to write
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*
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* @todo This needs to be handled by ralloc and writeRecord for
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* correctness. Right now, there is no way to atomically update a
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* page(!) To fix this, we need to change bufferManager's
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* implementation to use read/write (to prevent the OS from stealing
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* pages in the middle of updates), and alter kickPage to see what the
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* last LSN synced to disk was. If the log is too far behind, it will
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* need to either choose a different page, or call flushLog(). We may
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* need to implement a special version of fwrite() to do this
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* atomically. (write does not have to write all of the data that was
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* passed to it...)
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*/
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/*void writeLSN(long LSN, int pageid); */
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/**
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* @param pageid ID of page you want to read
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* @return LSN found on disk
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*/
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long readLSN(int pageid);
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/**
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* @param xid transaction id
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* @param rid recordid where you want to write
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* @param dat data you wish to write
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*/
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void writeRecord(int xid, lsn_t lsn, recordid rid, const void *dat);
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/**
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* @param xid transaction ID
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* @param rid
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* @param dat buffer for data
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*/
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void readRecord(int xid, recordid rid, void *dat);
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/**
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* @param page write page to disk, including correct LSN
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* @return 0 on success
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* @return error code on failure
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*/
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int flushPage(Page page);
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/*
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* this function does NOT write to disk, just drops the page from the active
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* pages
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* @param page to take out of buffer manager
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* @return 0 on success
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* @return error code on failure
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int dropPage(Page page);
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*/
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/**
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* all actions necessary when committing a transaction. Can assume that the log
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* has been written as well as any other actions that do not depend on the
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* buffer manager
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*
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* Basicly, this call is here because we used to do copy on write, and
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* it might be useful when locking is implemented.
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*
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* @param xid transaction ID
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* @return 0 on success
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* @return error code on failure
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*/
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int bufTransCommit(int xid, lsn_t lsn);
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/**
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*
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* Currently identical to bufTransCommit.
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*
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* @param xid transaction ID
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* @return 0 on success
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* @return error code on failure
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*/
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int bufTransAbort(int xid, lsn_t lsn);
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/**
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* will write out any dirty pages, assumes that there are no running
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* transactions
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*/
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void bufDeinit();
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/** @todo Global file descriptors are nasty. */
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extern int blobfd0;
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extern int blobfd1;
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#endif
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