• 列的相关性

• 表的全表扫描次数

• 索引使用次数

• Seq Scan全表扫描

3.2.1.

/*
* API struct for an index AM.  Note this must be stored in a single palloc'd
* chunk of memory.
*/
typedef struct IndexAmRoutine
{
    NodeTag		type;
    
    /*
* Total number of strategies (operators) by which we can traverse/search
* this AM.  Zero if AM does not have a fixed set of strategy assignments.
*/
    uint16		amstrategies;
    /* total number of support functions that this AM uses */
    uint16		amsupport;
    /* opclass options support function number or 0 */
    uint16		amoptsprocnum;
    /* does AM support ORDER BY indexed column's value? */
    bool		amcanorder;
    /* does AM support ORDER BY result of an operator on indexed column? */
    bool		amcanorderbyop;
    /* does AM support backward scanning? */
    bool		amcanbackward;
    /* does AM support UNIQUE indexes? */
    bool		amcanunique;
    /* does AM support multi-column indexes? */
    bool		amcanmulticol;
    /* does AM require scans to have a constraint on the first index column? */
    bool		amoptionalkey;
    /* does AM handle ScalarArrayOpExpr quals? */
    bool		amsearcharray;
    /* does AM handle IS NULL/IS NOT NULL quals? */
    bool		amsearchnulls;
    /* can index storage data type differ from column data type? */
    bool		amstorage;
    /* can an index of this type be clustered on? */
    bool		amclusterable;
    /* does AM handle predicate locks? */
    bool		ampredlocks;
    /* does AM support parallel scan? */
    bool		amcanparallel;
    /* does AM support columns included with clause INCLUDE? */
    bool		amcaninclude;
    /* does AM use maintenance_work_mem? */
    bool		amusemaintenanceworkmem;
    /* OR of parallel vacuum flags.  See vacuum.h for flags. */
    uint8		amparallelvacuumoptions;
    /* type of data stored in index, or InvalidOid if variable */
    Oid			amkeytype;

    /*
* If you add new properties to either the above or the below lists, then
* they should also (usually) be exposed via the property API (see
* IndexAMProperty at the top of the file, and utils/adt/amutils.c).
*/

    /* interface functions */
    ambuild_function ambuild;
    ambuildempty_function ambuildempty;
    aminsert_function aminsert;
    ambulkdelete_function ambulkdelete;
    amvacuumcleanup_function amvacuumcleanup;
    amcanreturn_function amcanreturn;	/* can be NULL */
    amcostestimate_function amcostestimate;
    amoptions_function amoptions;
    amproperty_function amproperty; /* can be NULL */
    ambuildphasename_function ambuildphasename; /* can be NULL */
    amvalidate_function amvalidate;
    amadjustmembers_function amadjustmembers;	/* can be NULL */
    ambeginscan_function ambeginscan;
    amrescan_function amrescan;
    amgettuple_function amgettuple; /* can be NULL */
    amgetbitmap_function amgetbitmap;	/* can be NULL */
    amendscan_function amendscan;
    ammarkpos_function ammarkpos;	/* can be NULL */
    amrestrpos_function amrestrpos; /* can be NULL */

    /* interface functions to support parallel index scans */
    amestimateparallelscan_function amestimateparallelscan; /* can be NULL */
    aminitparallelscan_function aminitparallelscan; /* can be NULL */
    amparallelrescan_function amparallelrescan; /* can be NULL */
} IndexAmRoutine;

/*
 * Btree handler function: return IndexAmRoutine with access method parameters
 * and callbacks.
 */
Datum
bthandler(PG_FUNCTION_ARGS)
{
	IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);

	amroutine->amstrategies = BTMaxStrategyNumber;
	amroutine->amsupport = BTNProcs;
	amroutine->amoptsprocnum = BTOPTIONS_PROC;
	amroutine->amcanorder = true;
	amroutine->amcanorderbyop = false;
	amroutine->amcanbackward = true;
	amroutine->amcanunique = true;
	amroutine->amcanmulticol = true;
	amroutine->amoptionalkey = true;
	amroutine->amsearcharray = true;
	amroutine->amsearchnulls = true;
	amroutine->amstorage = false;
	amroutine->amclusterable = true;
	amroutine->ampredlocks = true;
	amroutine->amcanparallel = true;
	amroutine->amcaninclude = true;
	amroutine->amusemaintenanceworkmem = false;
	amroutine->amparallelvacuumoptions =
		VACUUM_OPTION_PARALLEL_BULKDEL | VACUUM_OPTION_PARALLEL_COND_CLEANUP;
	amroutine->amkeytype = InvalidOid;

	amroutine->ambuild = btbuild;
	amroutine->ambuildempty = btbuildempty;
	amroutine->aminsert = btinsert;
	amroutine->ambulkdelete = btbulkdelete;
	amroutine->amvacuumcleanup = btvacuumcleanup;
	amroutine->amcanreturn = btcanreturn;
	amroutine->amcostestimate = btcostestimate;
	amroutine->amoptions = btoptions;
	amroutine->amproperty = btproperty;
	amroutine->ambuildphasename = btbuildphasename;
	amroutine->amvalidate = btvalidate;
	amroutine->amadjustmembers = btadjustmembers;
	amroutine->ambeginscan = btbeginscan;
	amroutine->amrescan = btrescan;
	amroutine->amgettuple = btgettuple;
	amroutine->amgetbitmap = btgetbitmap;
	amroutine->amendscan = btendscan;
	amroutine->ammarkpos = btmarkpos;
	amroutine->amrestrpos = btrestrpos;
	amroutine->amestimateparallelscan = btestimateparallelscan;
	amroutine->aminitparallelscan = btinitparallelscan;
	amroutine->amparallelrescan = btparallelrescan;

	PG_RETURN_POINTER(amroutine);
}

/*
 * Working state for btbuild and its callback.
 *
 * When parallel CREATE INDEX is used, there is a BTBuildState for each
 * participant.
 */
typedef struct BTBuildState
{
	bool		isunique;
	bool		nulls_not_distinct;
	bool		havedead;
	Relation	heap;
	BTSpool    *spool;

	/*
	 * spool2 is needed only when the index is a unique index. Dead tuples are
	 * put into spool2 instead of spool in order to avoid uniqueness check.
	 */
	BTSpool    *spool2;
	double		indtuples;

	/*
	 * btleader is only present when a parallel index build is performed, and
	 * only in the leader process. (Actually, only the leader has a
	 * BTBuildState.  Workers have their own spool and spool2, though.)
	 */
	BTLeader   *btleader;
} BTBuildState;

/*
 * Overall status record for index writing phase.
 */
typedef struct BTWriteState
{
	Relation	heap;
	Relation	index;
	BTScanInsert inskey;		/* generic insertion scankey */
	bool		btws_use_wal;	/* dump pages to WAL? 是否开启wal */
	BlockNumber btws_pages_alloced; /* # pages allocated 记录下一次申请page的块号*/
	BlockNumber btws_pages_written; /* # pages written out 已经写入文件的页面块号*/
	Page		btws_zeropage;	/* workspace for filling zeroes */
} BTWriteState;

/*
 * Status record for a btree page being built.  We have one of these
 * for each active tree level.
 */
typedef struct BTPageState
{
	Page		btps_page;		/* workspace for page building */
	BlockNumber btps_blkno;		/* block # to write this page at */
	IndexTuple	btps_lowkey;	/* page's strict lower bound pivot tuple */
	OffsetNumber btps_lastoff;	/* last item offset loaded */
	Size		btps_lastextra; /* last item's extra posting list space */
	uint32		btps_level;		/* tree level (0 = leaf) */
	Size		btps_full;		/* "full" if less than this much free space */
	struct BTPageState *btps_next;	/* link to parent level, if any */
} BTPageState;