PostgreSQL 统计信息pg_statistic格式及导入导出dump_stat - 兼容Oracle-阿里云开发者社区

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PostgreSQL 统计信息pg_statistic格式及导入导出dump_stat - 兼容Oracle

简介:

标签

PostgreSQL , dump_stat , 统计信息 , 导出导入


背景

《PostgreSQL 规格评估 - 微观、宏观、精准 多视角估算数据库性能(选型、做预算不求人)》

EXPLAIN是PG数据库用于输出SQL执行计划的语法,

1、生成的执行计划中包含COST一项。

如果校准了成本因子,COST可以和SQL实际执行时间对其。因子校对的方法如下,实际上每一种硬件,我们只需要校对一遍即可。

《优化器成本因子校对(disk,ssd,memory IO开销精算) - PostgreSQL real seq_page_cost & random_page_cost in disks,ssd,memory》

《优化器成本因子校对 - PostgreSQL explain cost constants alignment to timestamp》

校对因子如下:

#seq_page_cost = 1.0                    # measured on an arbitrary scale    
random_page_cost = 1.2                  # same scale as above    
#cpu_tuple_cost = 0.01                  # same scale as above    
#cpu_index_tuple_cost = 0.005           # same scale as above    
#cpu_operator_cost = 0.0025             # same scale as above    
    
# 以下不需要校对, 不考虑并行计算SQL    
parallel_tuple_cost = 0.1               # same scale as above    
parallel_setup_cost = 1000.0            # same scale as above    
effective_cache_size = 10GB    

2、评估COST还需要依赖统计信息柱状图:

涉及reltuples, relpages. 表示评估的记录数以及占用多少个数据块。注意源头的block_size可能和PG的不一致,占用多少个块需要转换一下。(show block_size可以查看数据块大小。)   
    
postgres=# \d pg_class    
                     Table "pg_catalog.pg_class"    
       Column        |     Type     | Collation | Nullable | Default     
---------------------+--------------+-----------+----------+---------    
 relname             | name         |           | not null |   -- 对象名  
 relnamespace        | oid          |           | not null |   -- 对象所属的schema, 对应pg_namespace.oid  
 reltype             | oid          |           | not null |     
 reloftype           | oid          |           | not null |     
 relowner            | oid          |           | not null |     
 relam               | oid          |           | not null |     
 relfilenode         | oid          |           | not null |     
 reltablespace       | oid          |           | not null |     
 relpages            | integer      |           | not null |   -- 评估的页数(单位为block_size)  
 reltuples           | real         |           | not null |   -- 评估的记录数  
 relallvisible       | integer      |           | not null |     
 reltoastrelid       | oid          |           | not null |     
 relhasindex         | boolean      |           | not null |     
 relisshared         | boolean      |           | not null |     
 relpersistence      | "char"       |           | not null |     
 relkind             | "char"       |           | not null |     
 relnatts            | smallint     |           | not null |     
 relchecks           | smallint     |           | not null |     
 relhasoids          | boolean      |           | not null |     
 relhaspkey          | boolean      |           | not null |     
 relhasrules         | boolean      |           | not null |     
 relhastriggers      | boolean      |           | not null |     
 relhassubclass      | boolean      |           | not null |     
 relrowsecurity      | boolean      |           | not null |     
 relforcerowsecurity | boolean      |           | not null |     
 relispopulated      | boolean      |           | not null |     
 relreplident        | "char"       |           | not null |     
 relispartition      | boolean      |           | not null |     
 relfrozenxid        | xid          |           | not null |     
 relminmxid          | xid          |           | not null |     
 relacl              | aclitem[]    |           |          |     
 reloptions          | text[]       |           |          |     
 relpartbound        | pg_node_tree |           |          |     
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)    
    
涉及   空值比例、平均列宽、唯一值比例或个数、高频值以及频率、柱状图分布、存储相关性、多值列(高频元素及比例、元素柱状图分布)。    
    
-- 这个是视图:  
  
postgres=# \d pg_stats     
                     View "pg_catalog.pg_stats"    
         Column         |   Type   | Collation | Nullable | Default     
------------------------+----------+-----------+----------+---------    
 schemaname             | name     |           |          |   -- 对象所属的schema  
 tablename              | name     |           |          |   -- 对象名  
 attname                | name     |           |          |   -- 列名  
 inherited              | boolean  |           |          |   -- 是否为继承表的统计信息(false时表示当前表的统计信息,true时表示包含所有继承表的统计信息)  
 null_frac              | real     |           |          |   -- 该列空值比例  
 avg_width              | integer  |           |          |   -- 该列平均长度  
 n_distinct             | real     |           |          |   -- 该列唯一值个数(-1表示唯一,小于1表示占比,大于等于1表示实际的唯一值个数)  
 most_common_vals       | anyarray |           |          |   -- 该列高频词  
 most_common_freqs      | real[]   |           |          |   -- 该列高频词对应的出现频率  
 histogram_bounds       | anyarray |           |          |   -- 该列柱状图(表示隔出的每个BUCKET的记录数均等)  
 correlation            | real     |           |          |   -- 该列存储相关性(-1到1的区间),绝对值越小,存储越离散。小于0表示反向相关,大于0表示正向相关  
 most_common_elems      | anyarray |           |          |   -- 该列为多值类型(数组)时,多值元素的高频词  
 most_common_elem_freqs | real[]   |           |          |   -- 多值元素高频词的出现频率  
 elem_count_histogram   | real[]   |           |          |   -- 多值元素的柱状图中,每个区间的非空唯一元素个数  
    
-- 这个是实际存储的数据(也就是要导入的部分):  
-- https://www.postgresql.org/docs/10/static/catalog-pg-statistic.html  
  
postgres=# \d pg_statistic    
             Table "pg_catalog.pg_statistic"    
   Column    |   Type   | Collation | Nullable | Default     
-------------+----------+-----------+----------+---------    
 starelid    | oid      |           | not null |   -- 对象OID,对应pg_class.oid  
 staattnum   | smallint |           | not null |   -- 该列在表中的位置序号,对应pg_attribute.attnum  
 stainherit  | boolean  |           | not null |   -- 是否为继承表的统计信息(false时表示当前表的统计信息,true时表示包含所有继承表的统计信息)  
 stanullfrac | real     |           | not null |   -- 空值比例  
 stawidth    | integer  |           | not null |   -- 平均长度  
 stadistinct | real     |           | not null |   -- 唯一值个数、比例  
 stakind1    | smallint |           | not null |   -- 表示第1个SLOT的统计信息分类编号  
 stakind2    | smallint |           | not null |   -- 表示第2个SLOT的统计信息分类编号  
 stakind3    | smallint |           | not null |   -- 表示第3个SLOT的统计信息分类编号  
 stakind4    | smallint |           | not null |   -- 表示第4个SLOT的统计信息分类编号  
 stakind5    | smallint |           | not null |   -- 表示第5个SLOT的统计信息分类编号  
 staop1      | oid      |           | not null |   -- 表示第1个SLOT的统计信息是用哪个operator生成的(例如统计柱状图边界,需要用到 "<" 这个操作符)  
 staop2      | oid      |           | not null |   -- 表示第2个SLOT的统计信息是用哪个operator生成的(例如统计柱状图边界,需要用到 "<" 这个操作符)  
 staop3      | oid      |           | not null |   -- 表示第3个SLOT的统计信息是用哪个operator生成的(例如统计柱状图边界,需要用到 "<" 这个操作符)  
 staop4      | oid      |           | not null |   -- 表示第4个SLOT的统计信息是用哪个operator生成的(例如统计柱状图边界,需要用到 "<" 这个操作符)  
 staop5      | oid      |           | not null |   -- 表示第5个SLOT的统计信息是用哪个operator生成的(例如统计柱状图边界,需要用到 "<" 这个操作符)  
 stanumbers1 | real[]   |           |          |   -- 表示第1个SLOT的以numeric[]为结果的统计信息,NULL说明这个SLOT分类没有numeric的统计信息。  
 stanumbers2 | real[]   |           |          |   -- 表示第2个SLOT的以numeric[]为结果的统计信息,NULL说明这个SLOT分类没有numeric的统计信息。  
 stanumbers3 | real[]   |           |          |   -- 表示第3个SLOT的以numeric[]为结果的统计信息,NULL说明这个SLOT分类没有numeric的统计信息。  
 stanumbers4 | real[]   |           |          |   -- 表示第4个SLOT的以numeric[]为结果的统计信息,NULL说明这个SLOT分类没有numeric的统计信息。  
 stanumbers5 | real[]   |           |          |   -- 表示第5个SLOT的以numeric[]为结果的统计信息,NULL说明这个SLOT分类没有numeric的统计信息。  
 stavalues1  | anyarray |           |          |   -- 表示第1个SLOT的以anyarray[]为结果的统计信息,NULL说明这个SLOT分类没有anyarray[]统计信息。数组类型为列的元素类型,或者列本身的类型。  
 stavalues2  | anyarray |           |          |   -- 表示第2个SLOT的以anyarray[]为结果的统计信息,NULL说明这个SLOT分类没有anyarray[]统计信息。数组类型为列的元素类型,或者列本身的类型。  
 stavalues3  | anyarray |           |          |   -- 表示第3个SLOT的以anyarray[]为结果的统计信息,NULL说明这个SLOT分类没有anyarray[]统计信息。数组类型为列的元素类型,或者列本身的类型。  
 stavalues4  | anyarray |           |          |   -- 表示第4个SLOT的以anyarray[]为结果的统计信息,NULL说明这个SLOT分类没有anyarray[]统计信息。数组类型为列的元素类型,或者列本身的类型。  
 stavalues5  | anyarray |           |          |   -- 表示第5个SLOT的以anyarray[]为结果的统计信息,NULL说明这个SLOT分类没有anyarray[]统计信息。数组类型为列的元素类型,或者列本身的类型。  
Indexes:    
    "pg_statistic_relid_att_inh_index" UNIQUE, btree (starelid, staattnum, stainherit)    

statkind的定义

src/include/catalog/pg_statistic.h

/*  
 * Currently, five statistical slot "kinds" are defined by core PostgreSQL,  
 * as documented below.  Additional "kinds" will probably appear in  
 * future to help cope with non-scalar datatypes.  Also, custom data types  
 * can define their own "kind" codes by mutual agreement between a custom  
 * typanalyze routine and the selectivity estimation functions of the type's  
 * operators.  
 *  
 * Code reading the pg_statistic relation should not assume that a particular  
 * data "kind" will appear in any particular slot.  Instead, search the  
 * stakind fields to see if the desired data is available.  (The standard  
 * function get_attstatsslot() may be used for this.)  
 */  
  
/*  
 * The present allocation of "kind" codes is:  
 *  
 *      1-99:           reserved for assignment by the core PostgreSQL project  
 *                              (values in this range will be documented in this file)  
 *      100-199:        reserved for assignment by the PostGIS project  
 *                              (values to be documented in PostGIS documentation)  
 *      200-299:        reserved for assignment by the ESRI ST_Geometry project  
 *                              (values to be documented in ESRI ST_Geometry documentation)  
 *      300-9999:       reserved for future public assignments  
 *  
 * For private use you may choose a "kind" code at random in the range  
 * 10000-30000.  However, for code that is to be widely disseminated it is  
 * better to obtain a publicly defined "kind" code by request from the  
 * PostgreSQL Global Development Group.  
 */  
  
/*  
 * In a "most common values" slot, staop is the OID of the "=" operator  
 * used to decide whether values are the same or not.  stavalues contains  
 * the K most common non-null values appearing in the column, and stanumbers  
 * contains their frequencies (fractions of total row count).  The values  
 * shall be ordered in decreasing frequency.  Note that since the arrays are  
 * variable-size, K may be chosen by the statistics collector.  Values should  
 * not appear in MCV unless they have been observed to occur more than once;  
 * a unique column will have no MCV slot.  
 */  
#define STATISTIC_KIND_MCV      1  
  
/*  
 * A "histogram" slot describes the distribution of scalar data.  staop is  
 * the OID of the "<" operator that describes the sort ordering.  (In theory,  
 * more than one histogram could appear, if a datatype has more than one  
 * useful sort operator.)  stavalues contains M (>=2) non-null values that  
 * divide the non-null column data values into M-1 bins of approximately equal  
 * population.  The first stavalues item is the MIN and the last is the MAX.  
 * stanumbers is not used and should be NULL.  IMPORTANT POINT: if an MCV  
 * slot is also provided, then the histogram describes the data distribution  
 * *after removing the values listed in MCV* (thus, it's a "compressed  
 * histogram" in the technical parlance).  This allows a more accurate  
 * representation of the distribution of a column with some very-common  
 * values.  In a column with only a few distinct values, it's possible that  
 * the MCV list describes the entire data population; in this case the  
 * histogram reduces to empty and should be omitted.  
 */  
#define STATISTIC_KIND_HISTOGRAM  2  
  
/*  
 * A "correlation" slot describes the correlation between the physical order  
 * of table tuples and the ordering of data values of this column, as seen  
 * by the "<" operator identified by staop.  (As with the histogram, more  
 * than one entry could theoretically appear.)  stavalues is not used and  
 * should be NULL.  stanumbers contains a single entry, the correlation  
 * coefficient between the sequence of data values and the sequence of  
 * their actual tuple positions.  The coefficient ranges from +1 to -1.  
 */  
#define STATISTIC_KIND_CORRELATION      3  
  
/*  
 * A "most common elements" slot is similar to a "most common values" slot,  
 * except that it stores the most common non-null *elements* of the column  
 * values.  This is useful when the column datatype is an array or some other  
 * type with identifiable elements (for instance, tsvector).  staop contains  
 * the equality operator appropriate to the element type.  stavalues contains  
 * the most common element values, and stanumbers their frequencies.  Unlike  
 * MCV slots, frequencies are measured as the fraction of non-null rows the  
 * element value appears in, not the frequency of all rows.  Also unlike  
 * MCV slots, the values are sorted into the element type's default order  
 * (to support binary search for a particular value).  Since this puts the  
 * minimum and maximum frequencies at unpredictable spots in stanumbers,  
 * there are two extra members of stanumbers, holding copies of the minimum  
 * and maximum frequencies.  Optionally, there can be a third extra member,  
 * which holds the frequency of null elements (expressed in the same terms:  
 * the fraction of non-null rows that contain at least one null element).  If  
 * this member is omitted, the column is presumed to contain no null elements.  
 *  
 * Note: in current usage for tsvector columns, the stavalues elements are of  
 * type text, even though their representation within tsvector is not  
 * exactly text.  
 */  
#define STATISTIC_KIND_MCELEM  4  
  
/*  
 * A "distinct elements count histogram" slot describes the distribution of  
 * the number of distinct element values present in each row of an array-type  
 * column.  Only non-null rows are considered, and only non-null elements.  
 * staop contains the equality operator appropriate to the element type.  
 * stavalues is not used and should be NULL.  The last member of stanumbers is  
 * the average count of distinct element values over all non-null rows.  The  
 * preceding M (>=2) members form a histogram that divides the population of  
 * distinct-elements counts into M-1 bins of approximately equal population.  
 * The first of these is the minimum observed count, and the last the maximum.  
 */  
#define STATISTIC_KIND_DECHIST  5  
  
/*  
 * A "length histogram" slot describes the distribution of range lengths in  
 * rows of a range-type column. stanumbers contains a single entry, the  
 * fraction of empty ranges. stavalues is a histogram of non-empty lengths, in  
 * a format similar to STATISTIC_KIND_HISTOGRAM: it contains M (>=2) range  
 * values that divide the column data values into M-1 bins of approximately  
 * equal population. The lengths are stored as float8s, as measured by the  
 * range type's subdiff function. Only non-null rows are considered.  
 */  
#define STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM  6  
  
/*  
 * A "bounds histogram" slot is similar to STATISTIC_KIND_HISTOGRAM, but for  
 * a range-type column.  stavalues contains M (>=2) range values that divide  
 * the column data values into M-1 bins of approximately equal population.  
 * Unlike a regular scalar histogram, this is actually two histograms combined  
 * into a single array, with the lower bounds of each value forming a  
 * histogram of lower bounds, and the upper bounds a histogram of upper  
 * bounds.  Only non-NULL, non-empty ranges are included.  
 */  
#define STATISTIC_KIND_BOUNDS_HISTOGRAM  7  

那么这些统计信息如何导入导出呢?

导出导入统计信息

https://postgrespro.com/docs/postgresproee/9.6/dump-stat.html

dump_stat这个插件是PostgreSQL pro推出的兼容9.6版本的导出统计信息的插件。

代码如下:

https://github.com/postgrespro/postgrespro/tree/PGPRO9_6

https://github.com/postgrespro/postgrespro/tree/PGPRO9_6/contrib/dump_stat

导出

通过dump_stat导出(导出的结构已经是SQL形式),然后通过SQL导入。

$ psql test -A    
test=# \t    
test=# \o dump_stat.sql    
test=# select dump_statistic();    

pg_statistic的每一条记录,产生一条如下SQL:

WITH upsert as (    
  UPDATE pg_catalog.pg_statistic SET column_name = expression [, ...]    
  WHERE to_schema_qualified_relation(starelid) = t_relname    
    AND to_attname(t_relname, staattnum) = t_attname    
    AND to_atttype(t_relname, staattnum) = t_atttype    
    AND stainherit = t_stainherit    
  RETURNING *)    
ins as (    
  SELECT expression [, ...]    
  WHERE NOT EXISTS (SELECT * FROM upsert)    
    AND to_attnum(t_relname, t_attname) IS NOT NULL    
    AND to_atttype(t_relname, t_attname) = t_atttype)    
INSERT INTO pg_catalog.pg_statistic SELECT * FROM ins;    
    
where expression can be one of:    
    
array_in(array_text, type_name::regtype::oid, -1)    
value::type_name    

stat导入的实际例子

(表示public.test表的info列的统计信息,如果存在则更新,不存在则插入。)

WITH   
  upsert as (   
    UPDATE pg_catalog.pg_statistic   
    SET   
      stanullfrac = 0, stawidth = 4, stadistinct = -1, stakind1 = 2, stakind2 = 3, stakind3 = 0, stakind4 = 0, stakind5 = 0, staop1 = 'pg_catalog.<(pg_catalog.text, pg_catalog.text)'::regoperator, staop2 = 'pg_catalog.<(pg_catalog.text, pg_catalog.text)'::regoperator, staop3 = '0'::regoperator, staop4 = '0'::regoperator, staop5 = '0'::regoperator, stanumbers1 = NULL::real[], stanumbers2 = '{-0.5}'::real[], stanumbers3 = NULL::real[], stanumbers4 = NULL::real[], stanumbers5 = NULL::real[], stavalues1 = array_in('{abc,cde,test}', 'pg_catalog.text'::regtype, -1)::anyarray, stavalues2 = NULL::anyarray, stavalues3 = NULL::anyarray, stavalues4 = NULL::anyarray, stavalues5 = NULL::anyarray   
    WHERE to_schema_qualified_relation(starelid) = 'public.test' AND to_attname('public.test', staattnum) = 'info' AND to_atttype('public.test', staattnum) = 'pg_catalog.text' AND stainherit = false   
    RETURNING *  
  ),   
  ins as (   
    SELECT   
      'public.test'::regclass,   
      to_attnum('public.test', 'info'),   
      'false'::boolean,   
      0::real,   
      4::integer,   
      -1::real,   
      2,  -- stakind=2 表示柱状图  
      3,  -- stakind=3 表示相关性  
      0,   
      0,   
      0,   
      'pg_catalog.<(pg_catalog.text, pg_catalog.text)'::regoperator,   
      'pg_catalog.<(pg_catalog.text, pg_catalog.text)'::regoperator,   
      '0'::regoperator,   
      '0'::regoperator,   
      '0'::regoperator,   
      NULL::real[],   
      '{-0.5}'::real[],   
      NULL::real[],   
      NULL::real[],   
      NULL::real[],   
      array_in('{abc,cde,test}', 'pg_catalog.text'::regtype, -1)::anyarray,   
      NULL::anyarray,   
      NULL::anyarray,   
      NULL::anyarray,   
      NULL::anyarray   
    WHERE NOT EXISTS (SELECT * FROM upsert) AND to_attnum('public.test', 'info') IS NOT NULL AND to_atttype('public.test', 'info') = 'pg_catalog.text'  
  )   
INSERT INTO pg_catalog.pg_statistic SELECT * FROM ins;  

导入

1、修改postgresql.conf,允许修改系统表,重启数据库生效配置

vi postgresql.conf  
    
allow_system_table_mods=on  
  
pg_ctl restart -m fast  

2、导入统计信息

-- 1 pg_class    
    
update pg_class set reltuples=?, relpages=? where oid=?;    
    
-- 2 pg_statistic    
    
WITH upsert as (    
  UPDATE pg_catalog.pg_statistic SET column_name = expression [, ...]    
  WHERE to_schema_qualified_relation(starelid) = t_relname    
    AND to_attname(t_relname, staattnum) = t_attname    
    AND to_atttype(t_relname, staattnum) = t_atttype    
    AND stainherit = t_stainherit    
  RETURNING *)    
ins as (    
  SELECT expression [, ...]    
  WHERE NOT EXISTS (SELECT * FROM upsert)    
    AND to_attnum(t_relname, t_attname) IS NOT NULL    
    AND to_atttype(t_relname, t_attname) = t_atttype)    
INSERT INTO pg_catalog.pg_statistic SELECT * FROM ins;    
    
where expression can be one of:    
    
array_in(array_text, type_name::regtype::oid, -1)    
value::type_name    

3、导入完成后,将allow_system_table_mods设置为off,重启数据库。

dump_statistic代码

CREATE FUNCTION dump_statistic(relid oid) RETURNS SETOF TEXT AS $$  
        DECLARE  
                result  text;  
                  
                cmd             text;           -- main query  
                in_args text;           -- args for insert  
                up_args text;           -- args for upsert  
                  
                fstaop  text := '%s::regoperator';  
                arr_in  text := 'array_in(%s, %s::regtype, -1)::anyarray';  
                  
                stacols text[] = ARRAY['stakind', 'staop',  
                                                           'stanumbers', 'stavalues' ];  
                  
                r               record;  
                i               int;  
                j               text;  
                ncols   int := 26;      -- number of columns in pg_statistic  
                  
                stanum  text[];         -- stanumbers{1, 5}  
                staval  text[];         -- stavalues{1, 5}  
                staop   text[];         -- staop{1, 5}  
                  
                relname text;           -- quoted relation name  
                attname text;           -- quoted attribute name  
                atttype text;           -- quoted attribute type  
                  
        BEGIN  
                for r in  
                                select * from pg_catalog.pg_statistic  
                                where starelid = relid  
                                        and get_namespace(starelid) != to_namespace('information_schema')  
                                        and get_namespace(starelid) != to_namespace('pg_catalog') loop  
                          
                        relname := to_schema_qualified_relation(r.starelid);  
                        attname := quote_literal(to_attname(relname, r.staattnum));  
                        atttype := quote_literal(to_atttype(relname, r.staattnum));  
                        relname := quote_literal(relname); -- redefine relname  
                          
                        in_args := '';  
                        up_args = 'stanullfrac = %s, stawidth = %s, stadistinct = %s, ';  
                          
                        cmd := 'WITH upsert as ( ' ||  
                                                'UPDATE pg_catalog.pg_statistic SET %s ' ||  
                                                'WHERE to_schema_qualified_relation(starelid) = ' || relname || ' '  
                                                        'AND to_attname(' || relname || ', staattnum) = ' || attname || ' '  
                                                        'AND to_atttype(' || relname || ', staattnum) = ' || atttype || ' '  
                                                        'AND stainherit = ' || r.stainherit || ' ' ||  
                                                'RETURNING *), ' ||  
                                   'ins as ( ' ||  
                                                'SELECT %s ' ||  
                                                'WHERE NOT EXISTS (SELECT * FROM upsert) ' ||  
                                                        'AND to_attnum(' || relname || ', ' || attname || ') IS NOT NULL '  
                                                        'AND to_atttype(' || relname || ', ' || attname || ') = ' || atttype || ') '  
                                   'INSERT INTO pg_catalog.pg_statistic SELECT * FROM ins;';  
                                          
                        for i in 1..ncols loop  
                                in_args := in_args || '%s';  
  
                                if i != ncols then  
                                        in_args := in_args || ', ';  
                                end if;  
                        end loop;  
                                  
                        for j in 1..4 loop  
                                for i in 1..5 loop  
                                        up_args := up_args || format('%s%s = %%s', stacols[j], i);  
  
                                        if i * j != 20 then  
                                                up_args := up_args || ', ';  
                                        end if;  
                                end loop;  
                        end loop;  
                          
                        cmd := format(cmd, up_args, in_args);   --prepare template for main query  
  
                        staop := array[format(fstaop, quote_literal(to_schema_qualified_operator(r.staop1))),  
                                                   format(fstaop, quote_literal(to_schema_qualified_operator(r.staop2))),  
                                                   format(fstaop, quote_literal(to_schema_qualified_operator(r.staop3))),  
                                                   format(fstaop, quote_literal(to_schema_qualified_operator(r.staop4))),  
                                                   format(fstaop, quote_literal(to_schema_qualified_operator(r.staop5)))];  
  
                        stanum := array[r.stanumbers1::text,  
                                                        r.stanumbers2::text,  
                                                        r.stanumbers3::text,  
                                                        r.stanumbers4::text,  
                                                        r.stanumbers5::text];  
                                                          
                        for i in 1..5 loop  
                                if stanum[i] is null then  
                                        stanum[i] := 'NULL::real[]';  
                                else  
                                        stanum[i] := '''' || stanum[i] || '''::real[]';  
                                end if;  
                        end loop;  
  
                        if r.stavalues1 is not null then  
                                staval[1] := format(arr_in, quote_literal(r.stavalues1),  
                                                                        quote_literal(  
                                                                                to_schema_qualified_type(  
                                                                                        anyarray_elemtype(r.stavalues1))));  
                        else  
                                staval[1] := 'NULL::anyarray';  
                        end if;  
  
                        if r.stavalues2 is not null then  
                                staval[2] := format(arr_in, quote_literal(r.stavalues2),  
                                                                        quote_literal(  
                                                                                to_schema_qualified_type(  
                                                                                        anyarray_elemtype(r.stavalues2))));  
                        else  
                                staval[2] := 'NULL::anyarray';  
                        end if;  
  
                        if r.stavalues3 is not null then  
                                staval[3] := format(arr_in, quote_literal(r.stavalues3),  
                                                                        quote_literal(  
                                                                                to_schema_qualified_type(  
                                                                                        anyarray_elemtype(r.stavalues3))));  
                        else  
                                staval[3] := 'NULL::anyarray';  
                        end if;  
  
                        if r.stavalues4 is not null then  
                                staval[4] := format(arr_in, quote_literal(r.stavalues4),  
                                                                        quote_literal(  
                                                                                to_schema_qualified_type(  
                                                                                        anyarray_elemtype(r.stavalues4))));  
                        else  
                                staval[4] := 'NULL::anyarray';  
                        end if;  
  
                        if r.stavalues5 is not null then  
                                staval[5] := format(arr_in, quote_literal(r.stavalues5),  
                                                                        quote_literal(  
                                                                                to_schema_qualified_type(  
                                                                                        anyarray_elemtype(r.stavalues5))));  
                        else  
                                staval[5] := 'NULL::anyarray';  
                        end if;  
                          
                        --DEBUG  
                        --staop := array['{arr}', '{arr}', '{arr}', '{arr}', '{arr}'];  
                        --stanum := array['{num}', '{num}', '{num}', '{num}', '{num}'];  
                        --staval := array['{val}', '{val}', '{val}', '{val}', '{val}'];  
  
                        result := format(cmd,  
                                                         r.stanullfrac,  
                                                         r.stawidth,  
                                                         r.stadistinct,  
                                                         -- stakind  
                                                         r.stakind1, r.stakind2, r.stakind3, r.stakind4, r.stakind5,  
                                                         -- staop  
                                                         staop[1], staop[2], staop[3], staop[4], staop[5],  
                                                         -- stanumbers  
                                                         stanum[1], stanum[2], stanum[3], stanum[4], stanum[5],  
                                                         -- stavalues  
                                                         staval[1], staval[2], staval[3], staval[4], staval[5],  
                                                           
                                                         -- first 6 columns  
                                                         format('%s::regclass', relname),  
                                                         format('to_attnum(%s, %s)', relname, attname),  
                                                         '''' || r.stainherit || '''::boolean',  
                                                         r.stanullfrac || '::real',  
                                                         r.stawidth || '::integer',  
                                                         r.stadistinct || '::real',  
                                                         -- stakind  
                                                         r.stakind1, r.stakind2, r.stakind3, r.stakind4, r.stakind5,  
                                                         -- staop  
                                                         staop[1], staop[2], staop[3], staop[4], staop[5],  
                                                         -- stanumbers  
                                                         stanum[1], stanum[2], stanum[3], stanum[4], stanum[5],  
                                                         -- stavalues  
                                                         staval[1], staval[2], staval[3], staval[4], staval[5]);  
  
                        return next result;  
                end loop;  
  
                return;  
        END;  
$$ LANGUAGE plpgsql;  

我们甚至可以将Oracle数据库的统计信息,平移到PG数据库,对齐需要的元素即可:

记录数、占用多少个数据块。每列的空值比例、平均列宽、唯一值比例或个数、高频值以及频率、柱状图分布、存储相关性、多值列(高频元素及比例、元素柱状图分布)。

好处:在迁移ORACLE数据时,可以关闭autovacuumm(提高导入速度),通过这种方法来导入统计信息。(只要元素对应即可,当然有些元素可能是ORACLE中不采集的,比如多值列的统计信息)。

参考

https://github.com/postgrespro/postgrespro/tree/PGPRO9_6/contrib/dump_stat

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