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linux+mysql+c plus plus 你懂的!

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分类: Mysql/postgreSQL

2013-04-09 11:03:17

例5.2 “CREATE INDEX 和 DROP INDEX的速度和效率”

这是一个展示CREATE INDEX 和 DROP INDEX的速度和效率的语句序列。对于小的表, 使用的时间不超过1秒,取决于我们使用快或慢的技术, 所以我们查看“rows affected” 输出来验证操作可以避免表的重建。对于一个大表,效率的差异是显而易见的,因为跳过表的重建可以节省大量的时间。
\! clear

\! echo "=== Create and drop index (small table, new/fast technique) ==="
\! echo
\! echo "Data size (kilobytes) before index created: "
\! du -k data/test/small_table.ibd
create index i_dtyp_small on small_table (data_type), algorithm=inplace;
\! echo "Data size after index created: "
\! du -k data/test/small_table.ibd
drop index i_dtyp_small on small_table, algorithm=inplace;

-- Compare against the older slower DDL.

\! echo "=== Create and drop index (small table, old/slow technique) ==="
\! echo
\! echo "Data size (kilobytes) before index created: "
\! du -k data/test/small_table.ibd
create index i_dtyp_small on small_table (data_type), algorithm=copy;
\! echo "Data size after index created: "
\! du -k data/test/small_table.ibd
drop index i_dtyp_small on small_table, algorithm=copy;

-- In the above example, we examined the "rows affected" number,
-- ideally looking for a zero figure. Let's try again with a larger
-- sample size, where we'll see that the actual time taken can
-- vary significantly.

\! echo "=== Create and drop index (big table, new/fast technique) ==="
\! echo
\! echo "Data size (kilobytes) before index created: "
\! du -k data/test/big_table.ibd
create index i_dtyp_big on big_table (data_type), algorithm=inplace;
\! echo "Data size after index created: "
\! du -k data/test/big_table.ibd
drop index i_dtyp_big on big_table, algorithm=inplace;

\! echo "=== Create and drop index (big table, old/slow technique) ==="
\! echo
\! echo "Data size (kilobytes) before index created: "
\! du -k data/test/big_table.ibd
create index i_dtyp_big on big_table (data_type), algorithm=copy;
\! echo "Data size after index created: "
\! du -k data/test/big_table.ibd
drop index i_dtyp_big on big_table, algorithm=copy;
运行以上代码会有如下的输出,浓缩为简洁和最重要的用粗体显示:
Query OK, 0 rows affected (0.00 sec)

=== Create and drop index (small table, new/fast technique) ===

Data size (kilobytes) before index created: 
384  data/test/small_table.ibd
Query OK, 0 rows affected (0.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

Data size after index created: 
432  data/test/small_table.ibd
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

Query OK, 0 rows affected (0.00 sec)

=== Create and drop index (small table, old/slow technique) ===

Data size (kilobytes) before index created: 
432  data/test/small_table.ibd
Query OK, 1678 rows affected (0.12 sec)
Records: 1678  Duplicates: 0  Warnings: 0

Data size after index created: 
448  data/test/small_table.ibd
Query OK, 1678 rows affected (0.10 sec)
Records: 1678  Duplicates: 0  Warnings: 0

Query OK, 0 rows affected (0.00 sec)

=== Create and drop index (big table, new/fast technique) ===

Data size (kilobytes) before index created: 
315392  data/test/big_table.ibd
Query OK, 0 rows affected (33.32 sec)
Records: 0  Duplicates: 0  Warnings: 0

Data size after index created: 
335872  data/test/big_table.ibd
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

Query OK, 0 rows affected (0.00 sec)

=== Create and drop index (big table, old/slow technique) ===

Data size (kilobytes) before index created: 
335872  data/test/big_table.ibd
Query OK, 1718272 rows affected (1 min 5.01 sec)
Records: 1718272  Duplicates: 0  Warnings: 0

Data size after index created: 
348160  data/test/big_table.ibd
Query OK, 1718272 rows affected (46.59 sec)
Records: 1718272  Duplicates: 0  Warnings: 0

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