fsm_internals.h

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/*-------------------------------------------------------------------------
 *
 * fsm_internals.h
 *    internal functions for free space map
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/fsm_internals.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef FSM_INTERNALS_H
#define FSM_INTERNALS_H
 
#include "storage/buf.h"
#include "storage/bufpage.h"
 
/*
 * Structure of a FSM page. See src/backend/storage/freespace/README for
 * details.
 */
typedef struct
{
    /*
     * fsm_search_avail() tries to spread the load of multiple backends by
     * returning different pages to different backends in a round-robin
     * fashion. fp_next_slot points to the next slot to be returned (assuming
     * there's enough space on it for the request). It's defined as an int,
     * because it's updated without an exclusive lock. uint16 would be more
     * appropriate, but int is more likely to be atomically
     * fetchable/storable.
     */
    int         fp_next_slot;
 
    /*
     * fp_nodes contains the binary tree, stored in array. The first
     * NonLeafNodesPerPage elements are upper nodes, and the following
     * LeafNodesPerPage elements are leaf nodes. Unused nodes are zero.
     */
    uint8       fp_nodes[FLEXIBLE_ARRAY_MEMBER];
} FSMPageData;
 
typedef FSMPageData *FSMPage;
 
/*
 * Number of non-leaf and leaf nodes, and nodes in total, on an FSM page.
 * These definitions are internal to fsmpage.c.
 */
#define NodesPerPage (BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - \
                      offsetof(FSMPageData, fp_nodes))
 
#define NonLeafNodesPerPage (BLCKSZ / 2 - 1)
#define LeafNodesPerPage (NodesPerPage - NonLeafNodesPerPage)
 
/*
 * Number of FSM "slots" on a FSM page. This is what should be used
 * outside fsmpage.c.
 */
#define SlotsPerFSMPage LeafNodesPerPage
 
/* Prototypes for functions in fsmpage.c */
extern int  fsm_search_avail(Buffer buf, uint8 minvalue, bool advancenext,
                             bool exclusive_lock_held);
extern uint8 fsm_get_avail(Page page, int slot);
extern uint8 fsm_get_max_avail(Page page);
extern bool fsm_set_avail(Page page, int slot, uint8 value);
extern bool fsm_truncate_avail(Page page, int nslots);
extern bool fsm_rebuild_page(Page page);
 
#endif                          /* FSM_INTERNALS_H */