Skip to content

M
mariadb
Commit c76c4206 authored by monty@hundin.mysql.fi's avatar monty@hundin.mysql.fi
Browse files
Options

Test of optimize table.

parent 7a45e7f2
Hide whitespace changes
Inline Side-by-side
Showing with 167 additions and 56 deletions
Docs/manual.texi
View file @ c76c4206
......@@ -3460,7 +3460,8 @@ select * from temporary_table, temporary_table as t2;
@end example
@item
@code{RENAME} doesn't work with @code{TEMPORARY} tables.
@code{RENAME} doesn't work with @code{TEMPORARY} tables or tables used in a
@code{MERGE} table.
@item
The optimiser may handle @code{DISTINCT} differently if you are using
......@@ -3554,6 +3555,7 @@ Minimum respective maximum possible @code{double} value.
@item
@code{LIMIT} on negative numbers are treated as big positive numbers.
@item
If you use @code{ALTER TABLE} to first add an @code{UNIQUE} index to a
table used in a @code{MERGE} table and then use @code{ALTER TABLE} to
......@@ -3701,6 +3703,9 @@ able to choose the right index when there is many to choose from. We should
also extend the info interface to get the key distribution for each index,
of @code{analyze} is run on all sub tables.
@item
@code{RENAME TABLE} on a table used in an active @code{MERGE} table may
corrupt the table.
@item
@code{SET SQL_DEFAULT_TABLE_TYPE=[MyISAM | INNODB | BDB | HEAP]}.
@end itemize
......@@ -3768,8 +3773,6 @@ in microseconds.
Add a configurable prompt to the @code{mysql} command line client, with
options like database in use, time and date...
@item
Add range checking to @code{MERGE} tables.
@item
Link the @code{myisampack} code into the server.
@item
Port of MySQL to BeOS.
......@@ -7789,6 +7792,10 @@ Multithreaded clients should use @code{mysql_thread_init()} and
If you want to recompile the perl DBD-MySQL module, you must get
Msql-Mysql-modules version 1.2218 or newer, because the older DBD modules
used the deprecated @code{drop_db()} call.
@item
@code{RAND(seed)} returns a different random number series in 4.0 than in
3.23; This was done to get @code{RAND(seed)} and @code{RAND(seed+1)} more
different.
@end itemize
@node Upgrading-from-3.22, Upgrading-from-3.21, Upgrading-from-3.23, Upgrade
......@@ -9137,12 +9144,14 @@ from usage by other threads. This has to do with the fact that on Windows,
you can't delete a file that is in use by another threads. (In the future,
we may find some way to work around this problem.)
@item @code{DROP TABLE} on a table that is in use by a @code{MERGE} table will not work
The @code{MERGE} handler does its table mapping hidden from MySQL.
Because Windows doesn't allow you to drop files that are open, you first
must flush all @code{MERGE} tables (with @code{FLUSH TABLES}) or drop the
@code{MERGE} table before dropping the table. We will fix this at the same
time we introduce @code{VIEW}s.
@item
@code{DROP TABLE} on a table that is in use by a @code{MERGE} table will
not work on windows becasue @code{MERGE} handler does the table mapping
hidden from the upper layer of MySQL. Because Windows doesn't allow you
to drop files that are open, you first must flush all @code{MERGE}
tables (with @code{FLUSH TABLES}) or drop the @code{MERGE} table before
dropping the table. We will fix this at the same time we introduce
@code{VIEW}s.
@item
@code{DATA DIRECTORY} and @code{INDEX DIRECTORY} directives in
@code{CREATE TABLE} is ignored on windows, because windows doesn't support
......@@ -13086,7 +13095,7 @@ DROP TABLE tmp;
@end example
The above way to solve this query is in effect a @code{UNION} of two queries.
@xref{UNION}.
@node Calculating days, example-AUTO_INCREMENT, Searching on two keys, Examples
@subsection Calculating visits per day
......@@ -25105,9 +25114,9 @@ option to @code{DELETE} may help. @xref{DELETE, , @code{DELETE}}.
* MySQL indexes:: How MySQL Uses Indexes
* Indexes:: Column Indexes
* Multiple-column indexes:: Multiple-Column Indexes
* Open tables:: Why So Many Open tables?
* Table cache:: How MySQL Opens and Closes Tables
* Creating many tables:: Drawbacks to Creating Large Numbers of Tables in the Same Database
* Open tables:: Why So Many Open tables?
@end menu
......@@ -25452,7 +25461,7 @@ created only from @code{VARCHAR} and @code{TEXT} columns.
Indexing always happens over the entire column and partial indexing is not
supported. See @ref{Fulltext Search} for details.
@node Multiple-column indexes, Table cache, Indexes, Optimising Database Structure
@node Multiple-column indexes, Open tables, Indexes, Optimising Database Structure
@subsection Multiple-Column Indexes
@cindex multi-column indexes
......@@ -25513,8 +25522,31 @@ For more information on the manner in which MySQL uses indexes to
improve query performance, see @ref{MySQL indexes, , MySQL
indexes}.
@node Open tables, Table cache, Multiple-column indexes, Optimising Database Structure
@subsection Why So Many Open tables?
@cindex tables, open
@cindex open tables
When you run @code{mysqladmin status}, you'll see something like this:
@example
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
@end example
@node Table cache, Creating many tables, Multiple-column indexes, Optimising Database Structure
This can be somewhat perplexing if you only have 6 tables.
MySQL is multithreaded, so it may have many queries on the same table
simultaneously. To minimise the problem with two threads having
different states on the same file, the table is opened independently by
each concurrent thread. This takes some memory but will normaly increase
performance. Wth ISAM and MyISAM tables this also requires one extra file
descriptor for the data file. With these table types the index file
descriptor is shared between all threads.
You can read more about this topic in the next section. @xref{Table cache}.
@node Table cache, Creating many tables, Open tables, Optimising Database Structure
@subsection How MySQL Opens and Closes Tables
@findex table_cache
......@@ -25549,11 +25581,27 @@ in increase the number of file descriptors available for MySQL with
the @code{--open-files-limit=#} startup option. @xref{Not enough file
handles}.
The cache of open tables can grow to a maximum of @code{table_cache}
(default 64; this can be changed with the @code{-O table_cache=#}
option to @code{mysqld}). A table is never closed, except when the
cache is full and another thread tries to open a table or if you use
@code{mysqladmin refresh} or @code{mysqladmin flush-tables}.
The cache of open tables will be keept at a level of @code{table_cache}
entries (default 64; this can be changed with the @code{-O
table_cache=#} option to @code{mysqld}). Note that in MySQL may
temporarly open even more tables to be able to execute queries.
A not used table is closed and removed from the table cache under the
following circumstances:
@itemize @bullet
@item
When the cache is full and a thread tries to open a table that is not in
the cache.
@item
When the cache contains more than @code{table_cache} entires and
a thread is not anymore using a table.
@item
When someone executes @code{mysqladmin refresh} or
@code{mysqladmin flush-tables}.
@item
When someone executes 'FLUSH TABLES'
@end itemize
When the table cache fills up, the server uses the following procedure
to locate a cache entry to use:
......@@ -25584,15 +25632,16 @@ If you are opening a table with the @code{HANDLER table_name OPEN}
statement, a dedicated table object is allocated for the thread.
This table object is not shared by other threads an will not be closed
until the thread calls @code{HANDLER table_name CLOSE} or the thread dies.
@xref{HANDLER}.
@xref{HANDLER}. When this happens, the table is put back in the table_cache
(if it isn't full).
You can check if your table cache is too small by checking the mysqld
variable @code{opened_tables}. If this is quite big, even if you
variable @code{Opened_tables}. If this is quite big, even if you
haven't done a lot of @code{FLUSH TABLES}, you should increase your table
cache. @xref{SHOW STATUS}.
@node Creating many tables, Open tables, Table cache, Optimising Database Structure
@node Creating many tables, , Table cache, Optimising Database Structure
@subsection Drawbacks to Creating Large Numbers of Tables in the Same Database
@cindex tables, too many
......@@ -25604,28 +25653,6 @@ every table that has to be opened, another must be closed. You can reduce
this overhead by making the table cache larger.
@node Open tables, , Creating many tables, Optimising Database Structure
@subsection Why So Many Open tables?
@cindex tables, open
@cindex open tables
When you run @code{mysqladmin status}, you'll see something like this:
@example
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
@end example
This can be somewhat perplexing if you only have 6 tables.
MySQL is multithreaded, so it may have many queries on the same
table simultaneously. To minimise the problem with two threads having
different states on the same file, the table is opened independently by
each concurrent thread. This takes some memory and one extra file
descriptor for the data file. The index file descriptor is shared
between all threads.
@node Optimising the Server, Disk issues, Optimising Database Structure, MySQL Optimisation
@section Optimising the MySQL Server
......@@ -30315,16 +30342,17 @@ Returns a random floating-point value in the range @code{0} to @code{1.0}.
If an integer argument @code{N} is specified, it is used as the seed value:
@example
mysql> select RAND();
-> 0.5925
-> 0.9233482386203
mysql> select RAND(20);
-> 0.1811
-> 0.15888261251047
mysql> select RAND(20);
-> 0.1811
-> 0.15888261251047
mysql> select RAND();
-> 0.2079
-> 0.63553050033332
mysql> select RAND();
-> 0.7888
-> 0.70100469486881
@end example
You can't use a column with @code{RAND()} values in an @code{ORDER BY}
clause, because @code{ORDER BY} would evaluate the column multiple times.
In MySQL Version 3.23, you can, however, do:
......@@ -30336,6 +30364,10 @@ table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000}.
Note that a @code{RAND()} in a @code{WHERE} clause will be re-evaluated
every time the @code{WHERE} is executed.
@code{RAND()} is not meant to be a perfect random generator, but instead a
fast way to generate add-hook random numbers that will be portable between
platforms for the same MySQL version.
@findex LEAST()
@item LEAST(X,Y,...)
With two or more arguments, returns the smallest (minimum-valued) argument.
......@@ -35416,17 +35448,59 @@ Change the @code{.MRG} file and issue a @code{FLUSH TABLE} on the
read the new definition file.
@end itemize
@menu
* MERGE table problems::
@end menu
@node MERGE table problems, , MERGE, MERGE
@subsection MERGE table problems.
The following are the known problems with @code{MERGE} tables:
@itemize @bullet
@item
@code{DELETE FROM merge_table} used without a @code{WHERE}
will only clear the mapping for the table, not delete everything in the
mapped tables.
@item
@code{RENAME TABLE} on a table used in an active @code{MERGE} table may
corrupt the table. This will be fixed in MySQL 4.0.x.
@item
Creation of a table of type @code{MERGE} doesn't check if the underlying
tables are of compatible types. If you use @code{MERGE} tables in this
fasion you are very likely to run into strange problems.
@item
If you use @code{ALTER TABLE} to first add an @code{UNIQUE} index to a
table used in a @code{MERGE} table and then use @code{ALTER TABLE} to
add a normal index on the @code{MERGE} table, the key order will be
different for the tables if there was an old not-unique key in the
table. This is because @code{ALTER TABLE} puts @code{UNIQUE} keys before
normal keys to be able to detect duplicate keys as early as possible.
@item
The range optimizer can't yet use @code{MERGE} table efficiently and may
sometimes produce not optimal joins. This will be fixed in MySQL 4.0.x.
@item
@code{DROP TABLE} on a table that is in use by a @code{MERGE} table will
not work on windows becasue @code{MERGE} handler does the table mapping
hidden from the upper layer of MySQL. Because Windows doesn't allow you
to drop files that are open, you first must flush all @code{MERGE}
tables (with @code{FLUSH TABLES}) or drop the @code{MERGE} table before
dropping the table. We will fix this at the same time we introduce
@code{VIEW}s.
@end itemize
@node ISAM, HEAP, MERGE, Table types
@section ISAM Tables
@cindex tables, ISAM
You can also use the deprecated ISAM table type. This will disappear
rather soon because @code{MyISAM} is a better implementation of the same
thing. ISAM uses a @code{B-tree} index. The index is stored in a file
with the @code{.ISM} extension, and the data is stored in a file with the
@code{.ISD} extension. You can check/repair ISAM tables with the
@code{isamchk} utility. @xref{Crash recovery}.
rather soon (probably in MySQL 4.1) because @code{MyISAM} is a better
implementation of the same thing. ISAM uses a @code{B-tree} index. The
index is stored in a file with the @code{.ISM} extension, and the data
is stored in a file with the @code{.ISD} extension. You can
check/repair ISAM tables with the @code{isamchk} utility. @xref{Crash
recovery}.
@code{ISAM} has the following features/properties:
......@@ -35459,6 +35533,7 @@ TABLE} statement:
mysql> ALTER TABLE tbl_name TYPE = MYISAM;
@end example
The embedded MySQL versions doesn't support ISAM tables.
@node HEAP, InnoDB, ISAM, Table types
@section HEAP Tables
......@@ -50583,7 +50658,7 @@ Fixed bug in record caches; for some queries, you could get
Added user level lock functions @code{GET_LOCK(string,timeout)},
@code{RELEASE_LOCK(string)}.
@item
Added @code{opened_tables} to @code{show status}.
Added @code{Opened_tables} to @code{show status}.
@item
Changed connect timeout to 3 seconds to make it somewhat harder
for crackers to kill @code{mysqld} through telnet + TCP/IP.
mysql-test/r/create.result
View file @ c76c4206
......@@ -68,3 +68,12 @@ select * from t2 where b="world";
a B
3 world
drop table t1,t2;
create table t1(x varchar(50) );
create table t2 select x from t1 where 1=2;
describe t1;
Field Type Null Key Default Extra
x varchar(50) YES NULL
describe t2;
Field Type Null Key Default Extra
x char(50) YES NULL
drop table t1,t2;
mysql-test/r/myisam.result
View file @ c76c4206
......@@ -31,3 +31,20 @@ check table t1;
Table Op Msg_type Msg_text
test.t1 check status OK
drop table t1;
create table t1 (a int not null auto_increment, b int not null, primary key (a), index(b));
insert into t1 (b) values (1),(2),(2),(2),(2);
optimize table t1;
Table Op Msg_type Msg_text
test.t1 optimize status OK
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Comment
t1 0 PRIMARY 1 a A 5 NULL NULL
t1 1 b 1 b A 1 NULL NULL
optimize table t1;
Table Op Msg_type Msg_text
test.t1 optimize status Table is already up to date
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Comment
t1 0 PRIMARY 1 a A 5 NULL NULL
t1 1 b 1 b A 1 NULL NULL
drop table t1;
mysql-test/t/create.test
View file @ c76c4206
......@@ -65,3 +65,13 @@ create table t2 (key (b)) select * from t1;
explain select * from t2 where b="world";
select * from t2 where b="world";
drop table t1,t2;
#
# Test types after CREATE ... SELECT
#
create table t1(x varchar(50) );
create table t2 select x from t1 where 1=2;
describe t1;
describe t2;
drop table t1,t2;
sql/item_func.cc
View file @ c76c4206
......@@ -621,8 +621,8 @@ double Item_func_rand::val()
{
if (arg_count)
{ // Only use argument once in query
ulong tmp=((ulong) args[0]->val_int())+55555555L;
randominit(&current_thd->rand,tmp,tmp/2);
ulong tmp=((ulong) args[0]->val_int());
randominit(&current_thd->rand,tmp*0x10001L+55555555L,tmp*0x10000001L);
#ifdef DELETE_ITEMS
delete args[0];
#endif
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7