WL#4351: Data Dictionary: relational schema
Affects: Server-6.2 — Status: Assigned — Priority: Medium
From the minutes of an architecture meeting in Stockholm, March 2008: > Information_Schema > > It was noted that Peter had agreed to list the underlying tables > and the views. Peter hereby lists. At this time it is only necessary to list the base tables, and only with respect to the information that is new or shocking. The base tables are analogous to the standard's DEFINITION_SCHEMA. There is no requirement that users can see them, they are internal. But INFORMATION_SCHEMA views will just select from them, so their contents are visible indirectly. We already have the makings of data dictionary tables. Peter proposes to (a) make changes affecting identifiers, (b) take what's already in mysql.* tables, (c) for items that are not in mysql.* use information_schema definitions and materialize. Name of Data Dictionary Database -------------------------------- Originally Peter wrote: " I have no name for the database where we'll store data dictionary. Indeed I cannot assume that there is such a thing, because WL#2760 leaves us a choice of storing separate instances of metadata tables in each database. But if we did have such a thing it would be called DEFINITION_SCHEMA /* because the standard has one */ MYSQL /* because mysql.* is where stuff is now */ DATA_DICTIONARY /* because that's what we're calling WL#2760 */ 'SYS____%' /* like other DBMSs e.g. DB2 has SYSCAT */ SUPER /* reminiscent of the original WL#2760 proposal */ DDD /* abbreviation of DATA DICTIONARY DATABASE. yuk. */ For neutrality in what follows, I'll preface names of new data-dictionary tables with 'Metadata.'. We'll replace it later. " However, Konstantin has informed Peter that the Stockholm decided that the name is 'mysql', same as the directory. Peter will remove this section soon. Changes Affecting Identifiers ----------------------------- Peter proposed in Stockholm that this is the appropriate time to change identifiers. He heard no objection there. Of course this means that Peter is assuming approval of WL#922 "Case-Sensitive Delimited Identifiers" plus WL#923 "Store regular identifiers in upper case". He is also assuming a lot about what will be in WL#922 and WL#923 by the time they're approved. 1. All identifier data types will be [VAR]CHAR(128). This is the amount that we allow for storage. This does not mean that maximum lengths automatically increase from what the MySQL Reference Manual currently says (http://dev.mysql.com/doc/refman/5.1/en/identifiers.html). 2. All Metadata table and column names will become upper case. This is already true for information_schema columns but not mysql.* columns. For example mysql.columns_priv has a column `Host`; it will change to HOST. This won't affect searches since they'll be case insensitive. 3. Identifiers are stored using 4-byte Unicode (UTF-8) with a Private Use Area. 4. Almost all identifier columns will become COLLATE UTF8_UNICODE_CS. There's currently no such collation. The CS stands for "case sensitive" but remember that regular identifiers get stored in upper case. There will be no flag to show an identifier was delimited. Base Tables like mysql.* ------------------------ These Metadata. tables have exactly the same contents as 6.0 mysql.* base tables except for the "Changes Affecting Identifiers" described earlier, and the addition of CATALOG VARCHAR(128) which will always be NULL. COLUMNS_PRIV DB EVENT FUNC HELP_CATEGORY HELP_KEYWORD HELP_RELATION HELP_TOPIC HOST NDB_BINLOG_INDEX PLUGIN PROC PROCS_PRIV SERVERS TABLES_PRIV TIME_ZONE TIME_ZONE_LEAP_SECOND TIME_ZONE_NAME TIME_ZONE_TRANSITION TIME_ZONE_TRANSITION_TYPE USER These mysql.* tables are not metadata and do not become Metadata tables: GENERAL_LOG ONLINE_BACKUP ONLINE_BACKUP_PROGRESS SLOW_LOG Base Tables like information_schema ----------------------------------- These Metadata. tables have exactly the same contents as 6.0 information_schema viewed tables except for the "Changes Affecting Identifiers" described earlier. Until now MYSQL has taken definitions from .frm files and from file headers. Henceforward it stores the definitions, since henceforward these are persistent base tables rather than just views. However the volatile data in TABLES columns, for example "row_count", is not stored and must be calculated during retrieval. FILES KEY_COLUMN_USAGE PARAMETERS PARTITIONS REFERENTIAL_CONSTRAINTS STATISTICS TABLES TABLESPACES (actually this doesn't exist in INFORMATION_SCHEMA yet) TRIGGERS VIEWS These information_schema tables are not metadata, or are fixed, or are due to bugs, and do not become Metadata tables: CHARACTER_SETS COLLATIONS COLLATION_CHARACTER_SET_APPLICABILITY ENGINES FALCON_DATABASE_IO FALCON_RECORD_CACHE_DETAIL FALCON_RECORD_CACHE_SUMMARY FALCON_SERIAL_LOG_INFO FALCON_SYSTEM_MEMORY_SUMMARY FALCON_SYNCOBJECTS FALCON_SYSTEM_MEMORY_DETAIL FALCON_TABLES FALCON_TRANSACTIONS FALCON_TRANSACTION_SUMMARY FALCON_VERSION GLOBAL_STATUS GLOBAL_VARIABLES PROCESSLIST PROFILING SESSION_STATUS SESSION_VARIABLES Other objects ------------- Peter urges reading the list of objects in WL#3713 Online backup: Selective rpl/backup of metadata https://intranet.mysql.com/worklog/Backup-BackLog/?tid=3713 He intends to follow the same classification scheme here. Metadata. has only a minority of the 60 items in the list. References ---------- dev-private email thread "Minutes of Stockholm meeting re changing WL#2760" https://intranet.mysql.com/secure/mailarchive/mail.php?folder=4&mail=23528
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