logrec_support.h

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#ifndef __LOGREC_SUPPORT_H
#define __LOGREC_SUPPORT_H

#include "lock.h"
#include "btree_page.h"
#include "alloc_page.h"
#include "stnode_page.h"

template<class PagePtr>
struct page_img_format_t {
    size_t beginning_bytes;

    size_t ending_bytes;

    char data[logrec_t::max_data_sz - 2 * sizeof(size_t)];

    int size() {
        return 2 * sizeof(size_t) + beginning_bytes + ending_bytes;
    }

    page_img_format_t(const PagePtr p) {
        /*
         * The mid-section of a btree page is usually not used, since head
         * entries are stored on the beginning of the page and variable-sized
         * "bodies" (i.e., key-value data) at the end of the page. This method
         * returns a pointer to the beginning of the unused part and its length.
         * The loc record then just contains the parts before and after the
         * unused section. For pages other than btree ones, the unused part
         * is either at the beginning or at the end of the page, and it must
         * be set to zero when replaying the log record.
         */

        size_t unused_length;
        char* unused;
        switch (p->tag()) {
            case t_alloc_p: {
                auto page = reinterpret_cast<alloc_page*>(p->get_generic_page());
                unused = page->unused_part(unused_length);
                break;
            }
            case t_stnode_p: {
                auto page = reinterpret_cast<stnode_page*>(p->get_generic_page());
                unused = page->unused_part(unused_length);
                break;
            }
            case t_btree_p: {
                auto page = reinterpret_cast<btree_page*>(p->get_generic_page());
                unused = page->unused_part(unused_length);
                break;
            }
            default:
                W_FATAL(eNOTIMPLEMENTED);
        }

        const char* pp_bin = (const char*)p->get_generic_page();
        beginning_bytes = unused - pp_bin;
        ending_bytes = sizeof(generic_page) - (beginning_bytes + unused_length);

        ::memcpy(data, pp_bin, beginning_bytes);
        ::memcpy(data + beginning_bytes, unused + unused_length, ending_bytes);
        // w_assert1(beginning_bytes >= btree_page::hdr_sz);
        w_assert1(beginning_bytes + ending_bytes <= sizeof(generic_page));
    }

    void apply(PagePtr page) {
        // w_assert1(beginning_bytes >= btree_page::hdr_sz);
        w_assert1(beginning_bytes + ending_bytes <= sizeof(generic_page));
        char* pp_bin = (char*)page->get_generic_page();
        ::memcpy(pp_bin, data, beginning_bytes);
        ::memcpy(pp_bin + sizeof(generic_page) - ending_bytes,
                 data + beginning_bytes, ending_bytes);
    }
};

#endif // __LOGREC_SUPPORT_H