src/include/storage/fsm_internals.h

   1 /*-------------------------------------------------------------------------
   2  *
   3  * fsm_internals.h
   4  *        internal functions for free space map
   5  *
   6  *
   7  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
   8  * Portions Copyright (c) 1994, Regents of the University of California
   9  *
  10  * src/include/storage/fsm_internals.h
  11  *
  12  *-------------------------------------------------------------------------
  13  */
  14 #ifndef FSM_INTERNALS_H
  15 #define FSM_INTERNALS_H
  16
  17 #include "storage/buf.h"
  18 #include "storage/bufpage.h"
  19
  20 /*
  21  * Structure of a FSM page. See src/backend/storage/freespace/README for
  22  * details.
  23  */
  24 typedef struct
  25 {
  26         /*
  27          * fsm_search_avail() tries to spread the load of multiple backends by
  28          * returning different pages to different backends in a round-robin
  29          * fashion. fp_next_slot points to the next slot to be returned (assuming
  30          * there's enough space on it for the request). It's defined as an int,
  31          * because it's updated without an exclusive lock. uint16 would be more
  32          * appropriate, but int is more likely to be atomically
  33          * fetchable/storable.
  34          */
  35         int                     fp_next_slot;
  36
  37         /*
  38          * fp_nodes contains the binary tree, stored in array. The first
  39          * NonLeafNodesPerPage elements are upper nodes, and the following
  40          * LeafNodesPerPage elements are leaf nodes. Unused nodes are zero.
  41          */
  42         uint8           fp_nodes[FLEXIBLE_ARRAY_MEMBER];
  43 } FSMPageData;
  44
  45 typedef FSMPageData *FSMPage;
  46
  47 /*
  48  * Number of non-leaf and leaf nodes, and nodes in total, on an FSM page.
  49  * These definitions are internal to fsmpage.c.
  50  */
  51 #define NodesPerPage (BLCKSZ - MAXALIGN(SizeOfPageHeaderData) - \
  52                                           offsetof(FSMPageData, fp_nodes))
  53
  54 #define NonLeafNodesPerPage (BLCKSZ / 2 - 1)
  55 #define LeafNodesPerPage (NodesPerPage - NonLeafNodesPerPage)
  56
  57 /*
  58  * Number of FSM "slots" on a FSM page. This is what should be used
  59  * outside fsmpage.c.
  60  */
  61 #define SlotsPerFSMPage LeafNodesPerPage
  62
  63 /* Prototypes for functions in fsmpage.c */
  64 extern int      fsm_search_avail(Buffer buf, uint8 minvalue, bool advancenext,
  65                                                          bool exclusive_lock_held);
  66 extern uint8 fsm_get_avail(Page page, int slot);
  67 extern uint8 fsm_get_max_avail(Page page);
  68 extern bool fsm_set_avail(Page page, int slot, uint8 value);
  69 extern bool fsm_truncate_avail(Page page, int nslots);
  70 extern bool fsm_rebuild_page(Page page);
  71
  72 #endif                                                  /* FSM_INTERNALS_H */