数据库内核月报 － 2016 / 05

----> SQL输入
----> 解析SQL，获取解析后的语法树
----> 分析、重写语法树，获取查询树
----> 根据重写、分析后的查询树计算各路径代价，从而选择一条成本最优的执行树
----> 根据执行树进行执行
----> 获取结果并返回

=> \d pg_class
      Table "pg_catalog.pg_class"
     Column     |   Type    | Modifiers
----------------+-----------+-----------
 relname        | name      | not null
 ...
 relpages       | integer   | not null
 reltuples      | real      | not null
 ...
 relkind        | "char"    | not null
 relnatts       | smallint  | not null
 ...
Indexes:
    "pg_class_oid_index" UNIQUE, btree (oid)
    "pg_class_relname_nsp_index" UNIQUE, btree (relname, relnamespace)
    "pg_class_tblspc_relfilenode_index" btree (reltablespace, relfilenode)

=> \d pg_statistic
  Table "pg_catalog.pg_statistic"
   Column    |   Type   | Modifiers
-------------+----------+-----------
 starelid    | oid      | not null
 staattnum   | smallint | not null
 stainherit  | boolean  | not null
 stanullfrac | real     | not null
 stawidth    | integer  | not null
 stadistinct | real     | not null
 stakind1    | smallint | not null
 stakind2    | smallint | not null
 stakind3    | smallint | not null
 stakind4    | smallint | not null
 stakind5    | smallint | not null
 staop1      | oid      | not null
 staop2      | oid      | not null
 staop3      | oid      | not null
 staop4      | oid      | not null
 staop5      | oid      | not null
 stanumbers1 | real[]   |
 stanumbers2 | real[]   |
 stanumbers3 | real[]   |
 stanumbers4 | real[]   |
 stanumbers5 | real[]   |
 stavalues1  | anyarray |
 stavalues2  | anyarray |
 stavalues3  | anyarray |
 stavalues4  | anyarray |
 stavalues5  | anyarray |
Indexes:
    "pg_statistic_relid_att_inh_index" UNIQUE, btree (starelid, staattnum, stainherit)

/*
 * These are the valid values of type LOCKMODE for all the standard lock
 * methods (both DEFAULT and USER).
 */

/* NoLock is not a lock mode, but a flag value meaning "don't get a lock" */
#define NoLock					0

#define AccessShareLock			1		/* SELECT */
#define RowShareLock			2		/* SELECT FOR UPDATE/FOR SHARE */
#define RowExclusiveLock		3		/* INSERT, UPDATE, DELETE */
#define ShareUpdateExclusiveLock 4		/* VACUUM (non-FULL),ANALYZE, CREATE
										 * INDEX CONCURRENTLY */
#define ShareLock				5		/* CREATE INDEX (WITHOUT CONCURRENTLY) */
#define ShareRowExclusiveLock	6		/* like EXCLUSIVE MODE, but allows ROW
										 * SHARE */
#define ExclusiveLock			7		/* blocks ROW SHARE/SELECT...FOR
										 * UPDATE */
#define AccessExclusiveLock		8		/* ALTER TABLE, DROP TABLE, VACUUM
										 * FULL, and unqualified LOCK TABLE */

typedef struct VacAttrStats
{
	/*
	 * These fields are set up by the main ANALYZE code before invoking the
	 * type-specific typanalyze function.
	 *
	 * Note: do not assume that the data being analyzed has the same datatype
	 * shown in attr, ie do not trust attr->atttypid, attlen, etc.  This is
	 * because some index opclasses store a different type than the underlying
	 * column/expression.  Instead use attrtypid, attrtypmod, and attrtype for
	 * information about the datatype being fed to the typanalyze function.
	 */
	Form_pg_attribute attr;		/* copy of pg_attribute row for column */
	Oid			attrtypid;		/* type of data being analyzed */
	int32		attrtypmod;		/* typmod of data being analyzed */
	Form_pg_type attrtype;		/* copy of pg_type row for attrtypid */
	MemoryContext anl_context;	/* where to save long-lived data */

	/*
	 * These fields must be filled in by the typanalyze routine, unless it
	 * returns FALSE.
	 */
	AnalyzeAttrComputeStatsFunc compute_stats;	/* function pointer */
	int			minrows;		/* Minimum # of rows wanted for stats */
	void	   *extra_data;		/* for extra type-specific data */

	/*
	 * These fields are to be filled in by the compute_stats routine. (They
	 * are initialized to zero when the struct is created.)
	 */
	bool		stats_valid;
	float4		stanullfrac;	/* fraction of entries that are NULL */
	int32		stawidth;		/* average width of column values */
	float4		stadistinct;	/* # distinct values */
	int16		stakind[STATISTIC_NUM_SLOTS];
	Oid			staop[STATISTIC_NUM_SLOTS];
	int			numnumbers[STATISTIC_NUM_SLOTS];
	float4	   *stanumbers[STATISTIC_NUM_SLOTS];
	int			numvalues[STATISTIC_NUM_SLOTS];
	Datum	   *stavalues[STATISTIC_NUM_SLOTS];

	/*
	 * These fields describe the stavalues[n] element types. They will be
	 * initialized to match attrtypid, but a custom typanalyze function might
	 * want to store an array of something other than the analyzed column's
	 * elements. It should then overwrite these fields.
	 */
	Oid			statypid[STATISTIC_NUM_SLOTS];
	int16		statyplen[STATISTIC_NUM_SLOTS];
	bool		statypbyval[STATISTIC_NUM_SLOTS];
	char		statypalign[STATISTIC_NUM_SLOTS];

	/*
	 * These fields are private to the main ANALYZE code and should not be
	 * looked at by type-specific functions.
	 */
	int			tupattnum;		/* attribute number within tuples */
	HeapTuple  *rows;			/* access info for std fetch function */
	TupleDesc	tupDesc;
	Datum	   *exprvals;		/* access info for index fetch function */
	bool	   *exprnulls;
	int			rowstride;
} VacAttrStats;