extent.h

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// extent.h

#pragma once

#include <iosfwd>
#include <string>
#include <vector>

#include "mongo/db/storage/mmap_v1/catalog/namespace.h"
#include "mongo/db/storage/mmap_v1/diskloc.h"

namespace mongo {

/* extents are datafile regions where all the records within the region
   belong to the same namespace.

(11:12:35 AM) dm10gen: when the extent is allocated, all its empty space is stuck into one big
    DeletedRecord
(11:12:55 AM) dm10gen: and that is placed on the free list
*/
#pragma pack(1)
struct Extent {
    enum { extentSignature = 0x41424344 };
    unsigned magic;
    DiskLoc myLoc;

    /* next/prev extent for this namespace */
    DiskLoc xnext;
    DiskLoc xprev;

    /* which namespace this extent is for.  this is just for troubleshooting really
       and won't even be correct if the collection were renamed!
    */
    Namespace nsDiagnostic;

    int length; /* size of the extent, including these fields */
    DiskLoc firstRecord;
    DiskLoc lastRecord;
    char _extentData[4];

    // -----

    bool validates(const DiskLoc diskLoc, std::vector<std::string>* errors = NULL) const;

    BSONObj dump() const;

    void dump(std::iostream& s) const;

    bool isOk() const {
        return magic == extentSignature;
    }
    void assertOk() const {
        verify(isOk());
    }

    static int HeaderSize() {
        return sizeof(Extent) - 4;
    }
};
#pragma pack()
}