Roland,
This actually helps a lot...thanx!
-Sheeri
On 9/23/08, Roland Bouman <[EMAIL PROTECTED]> wrote:
>
> Hi!
>
>
> > So, a few questions as to how MySQL does it, and hopefully a discussion
> on
>
>
> I can say what I have seen in MySQL 5.1 - most notably sql/sql_show.cc
>
>
> > how Drizzle should do it:
> > 1) Are the information_schema tables views or temporary tables?
>
>
> As far as I know they are not "views" in the sense of named schema
> objects defined by a query expression.
> They are temporary tables in the sense that they are transient
> in-memory structures that are bound to the thread (the current
> connection).
> In C they are defined through a special struct in table.h
>
> typedef struct st_schema_table
> {
> const char* table_name;
> ST_FIELD_INFO *fields_info;
> /* Create information_schema table */
> TABLE *(*create_table) (THD *thd, TABLE_LIST *table_list);
> /* Fill table with data */
> int (*fill_table) (THD *thd, TABLE_LIST *tables, COND *cond);
> /* Handle fileds for old SHOW */
> int (*old_format) (THD *thd, struct st_schema_table *schema_table);
> int (*process_table) (THD *thd, TABLE_LIST *tables, TABLE *table,
> bool res, LEX_STRING *db_name, LEX_STRING
> *table_name);
> int idx_field1, idx_field2;
> bool hidden;
> uint i_s_requested_object; /* the object we need to open(TABLE | VIEW)
> */
> } ST_SCHEMA_TABLE;
>
> I don't think this is the same as a table you create with CREATE TEMP
> TABLE.
>
>
> > 2) Where are the definitions stored for the information_schema tables?
>
>
> If you mean, the column layout that is defined as a list in the C code.
> The member
>
> ST_FIELD_INFO *fields_info;
>
> of ST_SCHEMA_TABLE holds this list.
>
> The specific IS table layouts are hardwired in sql_show.cc
>
> For example, here is the column layout for I_S.processlist:
>
> ST_FIELD_INFO processlist_fields_info[]=
> {
> {"ID", 4, MYSQL_TYPE_LONGLONG, 0, 0, "Id", SKIP_OPEN_TABLE},
> {"USER", 16, MYSQL_TYPE_STRING, 0, 0, "User", SKIP_OPEN_TABLE},
> {"HOST", LIST_PROCESS_HOST_LEN, MYSQL_TYPE_STRING, 0, 0, "Host",
> SKIP_OPEN_TABLE},
> {"DB", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 1, "Db", SKIP_OPEN_TABLE},
> {"COMMAND", 16, MYSQL_TYPE_STRING, 0, 0, "Command", SKIP_OPEN_TABLE},
> {"TIME", 7, MYSQL_TYPE_LONGLONG, 0, 0, "Time", SKIP_OPEN_TABLE},
> {"STATE", 64, MYSQL_TYPE_STRING, 0, 1, "State", SKIP_OPEN_TABLE},
> {"INFO", PROCESS_LIST_INFO_WIDTH, MYSQL_TYPE_STRING, 0, 1, "Info",
> SKIP_OPEN_TABLE},
> {0, 0, MYSQL_TYPE_STRING, 0, 0, 0, SKIP_OPEN_TABLE}
>
> };
>
> > 3) How and when do the definitions get loaded?
>
>
> If you mean by "definition" the column layout, then I think it is
> loaded from the start on. The arrays of ST_FIELD_INFO are global
> variables.
> I am not entirely sure how and when the data is loaded.
>
>
> > I see these questions (particularly #3) as important particularly for
> > plugins, as some plugins will (heck, I'd probably argue that most of the
> > major ones *should*) add to the information_schema database.
>
>
> well, I believe that for information schema plugins, the definition is
> loaded at least upon INSTALL plugin, but also on server startup (for
> those plugins already installed)
>
> I hope this helps,
>
> Roland
> >
> > --
> > - Sheeri K. Cabral
> >
> >
> >
> > _______________________________________________
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> >
> >
>
>
>
>
> --
> Roland Bouman
> http://rpbouman.blogspot.com/
>
--
- Sheeri K. Cabral
Note: Currently I work for The Pythian Group (http://www.pythian.com/ ), a
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I have a webpage with tips on how to find a DBA:
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