[统计信息]1.Oracle统计信息概述
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（一）统计信息分类
Oracle的统计信息可以分为如下6类：
| 统计信息分类 | 作用 |
| 表的统计信息 | 包含记录数、表块的数量、平均行长度等 |
| 索引的统计信息 | 包含索引的高度、叶子块的数量、聚簇因子等 |
| 列的统计信息 | 包含列的distinct值、列的null值的数量、列的最小值、列的最大值以及直方图等 |
| 系统统计信息 |
系统统计信息用于描述Oracle所在服务器的系统处理能力，它包含了CPU和I/O两个维度，借助于系统统计信息，Oracle可以更清楚的指导服务器的实际处理能力 |
| 数据字典统计信息 | 数据字典统计信息用于描述数据库字典基表（如tab$,ind$等）、基表的索引、以及对应列的详细信息 |
| 内部对象统计信息 | 内部对象统计信息用于描述Oracle的一些内部表（如x$系列表）的详细信息，他的维度和普通表的统计信息维度类似，只不过其表块的数量为0，因为x$系列表实际上是Oracle自定义的内存结构，并不占用实际空间 |
（二）统计信息收集与删除
（1）使用analyze来收集/删除统计信息
--收集索引的统计信息 analyze index pk_id compute statistics; -- 删除索引pk_id的统计信息 analyze index pk_id delete statistics; -- 只对表收集统计信息，不对列和索引收集，以采样20%的方式收集 analyze table test01 estimate statistics sample 20 percent for table; -- 收集test01的col1和col2的统计信息 analyze table test01 compute statistics for columns col1,col2; -- 一次性收集test01 表、列、索引的统计信息 analyze table test01 compute statistics; -- 删除test01 表、列、索引的统计信息 analyze table test01 delete statistics;
（2）使用DBMS_STATS来收集/删除统计信息
收集统计信息：
- GATHER_TABLE_STATS：用来收集目标表、表上的列、表上的索引的统计信息；
- GATHER_INDEX_STATS：用于收集索引的统计信息；
- GATHER_SCHEMA_STATS：用于收集schema下所有对象的统计信息
- GATHER_DATABASE_STATS：用于收集全库的统计信息
删除统计信息：
- DELETE_COLUMN_STATS ： 删除列的统计信息
- DELETE_INDEX_STATS ： 删除索引的统计信息
- DELETE_TABLE_STATS ：删除表的统计信息
- DELETE_SCHEMA_STATS ：删除schema的统计信息
- DELETE_DATABASE_STATS ：删除数据库的统计信息
（三）统计信息收集方法比较
- analyze不能正确收集分区表的统计信息。analyze只会收集最底层对象的统计信息，然后推导和汇总出高一级的统计信息。例如对于分区表，analyze会统计出分区的统计信息，然后汇总出表的统计信息，对于表的行数，可以由分区汇总得到，但是对于列的distinct值，无法得到正确值。
- analyze命令不能并行收集统计信息，而dbms_stats可以。
- analyze命令可以收集行迁移/行链接、索引的结构等信息，而dbms_stats不行。
（四）查看统计信息
可以使用sosi.txt脚本收集统计信息，该脚本记录了表、分区、子分区级别的统计信息，sosi.txt脚本如下：
1 set echo off 2 set scan on 3 set lines 150 4 set pages 66 5 set verify off 6 set feedback off 7 set termout off 8 column uservar new_value Table_Owner noprint 9 select user uservar from dual; 10 set termout on 11 column TABLE_NAME heading "Tables owned by &Table_Owner" format a30 12 select table_name from dba_tables where owner=upper(\'&Table_Owner\') order by 1 13 / 14 undefine table_name 15 undefine owner 16 prompt 17 accept owner prompt \'Please enter Name of Table Owner (Null = &Table_Owner): \' 18 accept table_name prompt \'Please enter Table Name to show Statistics for: \' 19 column TABLE_NAME heading "Table|Name" format a15 20 column PARTITION_NAME heading "Partition|Name" format a15 21 column SUBPARTITION_NAME heading "SubPartition|Name" format a15 22 column NUM_ROWS heading "Number|of Rows" format 9,999,999,990 23 column BLOCKS heading "Blocks" format 999,990 24 column EMPTY_BLOCKS heading "Empty|Blocks" format 999,999,990 25 column AVG_SPACE heading "Average|Space" format 9,990 26 column CHAIN_CNT heading "Chain|Count" format 999,990 27 column AVG_ROW_LEN heading "Average|Row Len" format 990 28 column COLUMN_NAME heading "Column|Name" format a25 29 column NULLABLE heading Null|able format a4 30 column NUM_DISTINCT heading "Distinct|Values" format 999,999,990 31 column NUM_NULLS heading "Number|Nulls" format 9,999,990 32 column NUM_BUCKETS heading "Number|Buckets" format 990 33 column DENSITY heading "Density" format 990 34 column INDEX_NAME heading "Index|Name" format a15 35 column UNIQUENESS heading "Unique" format a9 36 column BLEV heading "B|Tree|Level" format 90 37 column LEAF_BLOCKS heading "Leaf|Blks" format 990 38 column DISTINCT_KEYS heading "Distinct|Keys" format 9,999,999,990 39 column AVG_LEAF_BLOCKS_PER_KEY heading "Average|Leaf Blocks|Per Key" format 99,990 40 column AVG_DATA_BLOCKS_PER_KEY heading "Average|Data Blocks|Per Key" format 99,990 41 column CLUSTERING_FACTOR heading "Cluster|Factor" format 999,999,990 42 column COLUMN_POSITION heading "Col|Pos" format 990 43 column col heading "Column|Details" format a24 44 column COLUMN_LENGTH heading "Col|Len" format 9,990 45 column GLOBAL_STATS heading "Global|Stats" format a6 46 column USER_STATS heading "User|Stats" format a6 47 column SAMPLE_SIZE heading "Sample|Size" format 9,999,999,990 48 column to_char(t.last_analyzed,\'MM-DD-YYYY\') heading "Date|MM-DD-YYYY" format a10 49 prompt 50 prompt *********** 51 prompt Table Level 52 prompt *********** 53 prompt 54 select 55 TABLE_NAME, 56 NUM_ROWS, 57 BLOCKS, 58 EMPTY_BLOCKS, 59 AVG_SPACE, 60 CHAIN_CNT, 61 AVG_ROW_LEN, 62 GLOBAL_STATS, 63 USER_STATS, 64 SAMPLE_SIZE, 65 to_char(t.last_analyzed,\'MM-DD-YYYY\') 66 from dba_tables t 67 where 68 owner = upper(nvl(\'&&Owner\',user)) 69 and table_name = upper(\'&&Table_name\') 70 / 71 select 72 COLUMN_NAME, 73 decode(t.DATA_TYPE, 74 \'NUMBER\',t.DATA_TYPE||\'(\'|| 75 decode(t.DATA_PRECISION, 76 null,t.DATA_LENGTH||\')\', 77 t.DATA_PRECISION||\',\'||t.DATA_SCALE||\')\'), 78 \'DATE\',t.DATA_TYPE, 79 \'LONG\',t.DATA_TYPE, 80 \'LONG RAW\',t.DATA_TYPE, 81 \'ROWID\',t.DATA_TYPE, 82 \'MLSLABEL\',t.DATA_TYPE, 83 t.DATA_TYPE||\'(\'||t.DATA_LENGTH||\')\') ||\' \'|| 84 decode(t.nullable, 85 \'N\',\'NOT NULL\', 86 \'n\',\'NOT NULL\', 87 NULL) col, 88 NUM_DISTINCT, 89 DENSITY, 90 NUM_BUCKETS, 91 NUM_NULLS, 92 GLOBAL_STATS, 93 USER_STATS, 94 SAMPLE_SIZE, 95 to_char(t.last_analyzed,\'MM-DD-YYYY\') 96 from dba_tab_columns t 97 where 98 table_name = upper(\'&Table_name\') 99 and owner = upper(nvl(\'&Owner\',user)) 100 / 101 select 102 INDEX_NAME, 103 UNIQUENESS, 104 BLEVEL BLev, 105 LEAF_BLOCKS, 106 DISTINCT_KEYS, 107 NUM_ROWS, 108 AVG_LEAF_BLOCKS_PER_KEY, 109 AVG_DATA_BLOCKS_PER_KEY, 110 CLUSTERING_FACTOR, 111 GLOBAL_STATS, 112 USER_STATS, 113 SAMPLE_SIZE, 114 to_char(t.last_analyzed,\'MM-DD-YYYY\') 115 from 116 dba_indexes t 117 where 118 table_name = upper(\'&Table_name\') 119 and table_owner = upper(nvl(\'&Owner\',user)) 120 / 121 break on index_name 122 select 123 i.INDEX_NAME, 124 i.COLUMN_NAME, 125 i.COLUMN_POSITION, 126 decode(t.DATA_TYPE, 127 \'NUMBER\',t.DATA_TYPE||\'(\'|| 128 decode(t.DATA_PRECISION, 129 null,t.DATA_LENGTH||\')\', 130 t.DATA_PRECISION||\',\'||t.DATA_SCALE||\')\'), 131 \'DATE\',t.DATA_TYPE, 132 \'LONG\',t.DATA_TYPE, 133 \'LONG RAW\',t.DATA_TYPE, 134 \'ROWID\',t.DATA_TYPE, 135 \'MLSLABEL\',t.DATA_TYPE, 136 t.DATA_TYPE||\'(\'||t.DATA_LENGTH||\')\') ||\' \'|| 137 decode(t.nullable, 138 \'N\',\'NOT NULL\', 139 \'n\',\'NOT NULL\', 140 NULL) col 141 from 142 dba_ind_columns i, 143 dba_tab_columns t 144 where 145 i.table_name = upper(\'&Table_name\') 146 and owner = upper(nvl(\'&Owner\',user)) 147 and i.table_name = t.table_name 148 and i.column_name = t.column_name 149 order by index_name,column_position 150 / 151 prompt 152 prompt *************** 153 prompt Partition Level 154 prompt *************** 155 select 156 PARTITION_NAME, 157 NUM_ROWS, 158 BLOCKS, 159 EMPTY_BLOCKS, 160 AVG_SPACE, 161 CHAIN_CNT, 162 AVG_ROW_LEN, 163 GLOBAL_STATS, 164 USER_STATS, 165 SAMPLE_SIZE, 166 to_char(t.last_analyzed,\'MM-DD-YYYY\') 167 from 168 dba_tab_partitions t 169 where 170 table_owner = upper(nvl(\'&&Owner\',user)) 171 and table_name = upper(\'&&Table_name\') 172 order by partition_position 173 / 174 break on partition_name 175 select 176 PARTITION_NAME, 177 COLUMN_NAME, 178 NUM_DISTINCT, 179 DENSITY, 180 NUM_BUCKETS, 181 NUM_NULLS, 182 GLOBAL_STATS, 183 USER_STATS, 184 SAMPLE_SIZE, 185 to_char(t.last_analyzed,\'MM-DD-YYYY\') 186 from 187 dba_PART_COL_STATISTICS t 188 where 189 table_name = upper(\'&Table_name\') 190 and owner = upper(nvl(\'&Owner\',user)) 191 / 192 break on partition_name 193 select 194 t.INDEX_NAME, 195 t.PARTITION_NAME, 196 t.BLEVEL BLev, 197 t.LEAF_BLOCKS, 198 t.DISTINCT_KEYS, 199 t.NUM_ROWS, 200 t.AVG_LEAF_BLOCKS_PER_KEY, 201 t.AVG_DATA_BLOCKS_PER_KEY, 202 t.CLUSTERING_FACTOR, 203 t.GLOBAL_STATS, 204 t.USER_STATS, 205 t.SAMPLE_SIZE, 206 to_char(t.last_analyzed,\'MM-DD-YYYY\') 207 from 208 dba_ind_partitions t, 209 dba_indexes i 210 where 211 i.table_name = upper(\'&Table_name\') 212 and i.table_owner = upper(nvl(\'&Owner\',user)) 213 and i.owner = t.index_owner 214 and i.index_name=t.index_name 215 / 216 prompt 217 prompt *************** 218 prompt SubPartition Level 219 prompt *************** 220 select 221 PARTITION_NAME, 222 SUBPARTITION_NAME, 223 NUM_ROWS, 224 BLOCKS, 225 EMPTY_BLOCKS, 226 AVG_SPACE, 227 CHAIN_CNT, 228 AVG_ROW_LEN, 229 GLOBAL_STATS, 230 USER_STATS, 231 SAMPLE_SIZE, 232 to_char(t.last_analyzed,\'MM-DD-YYYY\') 233 from 234 dba_tab_subpartitions t 235 where 236 table_owner = upper(nvl(\'&&Owner\',user)) 237 and table_name = upper(\'&&Table_name\') 238 order by SUBPARTITION_POSITION 239 / 240 break on partition_name 241 select 242 p.PARTITION_NAME, 243 t.SUBPARTITION_NAME, 244 t.COLUMN_NAME, 245 t.NUM_DISTINCT, 246 t.DENSITY, 247 t.NUM_BUCKETS, 248 t.NUM_NULLS, 249 t.GLOBAL_STATS, 250 t.USER_STATS, 251 t.SAMPLE_SIZE, 252 to_char(t.last_analyzed,\'MM-DD-YYYY\') 253 from 254 dba_SUBPART_COL_STATISTICS t, 255 dba_tab_subpartitions p 256 where 257 t.table_name = upper(\'&Table_name\') 258 and t.owner = upper(nvl(\'&Owner\',user)) 259 and t.subpartition_name = p.subpartition_name 260 and t.owner = p.table_owner 261 and t.table_name=p.table_name 262 / 263 break on partition_name 264 select 265 t.INDEX_NAME, 266 t.PARTITION_NAME, 267 t.SUBPARTITION_NAME, 268 t.BLEVEL BLev, 269 t.LEAF_BLOCKS, 270 t.DISTINCT_KEYS, 271 t.NUM_ROWS, 272 t.AVG_LEAF_BLOCKS_PER_KEY, 273 t.AVG_DATA_BLOCKS_PER_KEY, 274 t.CLUSTERING_FACTOR, 275 t.GLOBAL_STATS, 276 t.USER_STATS, 277 t.SAMPLE_SIZE, 278 to_char(t.last_analyzed,\'MM-DD-YYYY\') 279 from 280 dba_ind_subpartitions t, 281 dba_indexes i 282 where 283 i.table_name = upper(\'&Table_name\') 284 and i.table_owner = upper(nvl(\'&Owner\',user)) 285 and i.owner = t.index_owner 286 and i.index_name=t.index_name 287 / 288 clear breaks Oracle 和 SQLSERVER 重新获取统计信息的方法