checksum.h File Reference

#include "storage/block.h"

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Functions
uint16	pg_checksum_page (char *page, BlockNumber blkno)

Function Documentation

pg_checksum_page()

uint16 pg_checksum_page ( char *  page, BlockNumber  blkno  )

extern

Definition at line 187 of file checksum_impl.h.

{
    PGChecksummablePage *cpage = (PGChecksummablePage *) page;
    uint16      save_checksum;
    uint32      checksum;
 
    /* We only calculate the checksum for properly-initialized pages */
    Assert(!PageIsNew((Page) page));
 
    /*
     * Save pd_checksum and temporarily set it to zero, so that the checksum
     * calculation isn't affected by the old checksum stored on the page.
     * Restore it after, because actually updating the checksum is NOT part of
     * the API of this function.
     */
    save_checksum = cpage->phdr.pd_checksum;
    cpage->phdr.pd_checksum = 0;
    checksum = pg_checksum_block(cpage);
    cpage->phdr.pd_checksum = save_checksum;
 
    /* Mix in the block number to detect transposed pages */
    checksum ^= blkno;
 
    /*
     * Reduce to a uint16 (to fit in the pd_checksum field) with an offset of
     * one. That avoids checksums of zero, which seems like a good idea.
     */
    return (uint16) ((checksum % 65535) + 1);
}

References Assert, fb(), PageIsNew(), and pg_checksum_block().

Referenced by modify_rel_block(), page_checksum_internal(), PageIsVerified(), PageSetChecksumCopy(), PageSetChecksumInplace(), rewriteVisibilityMap(), scan_file(), and verify_page_checksum().