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-rw-r--r--Docs/manual.texi83
-rwxr-xr-xvio/test-sslbin42096 -> 42160 bytes
2 files changed, 46 insertions, 37 deletions
diff --git a/Docs/manual.texi b/Docs/manual.texi
index 8e89c9d09d2..7a67a73d05f 100644
--- a/Docs/manual.texi
+++ b/Docs/manual.texi
@@ -3706,7 +3706,7 @@ list in this manual. @xref{TODO}.
* Missing Transactions:: Transactions
* Missing Triggers:: Triggers
* Missing Foreign Keys:: Foreign Keys
-* Broken Foreign KEY:: Reasons NOT to Use Foreign Keys constraints
+* Broken Foreign KEY:: Why We Did Not Implement Foreign Keys
* Missing Views:: Views
* Missing comments:: @samp{--} as the start of a comment
@end menu
@@ -3989,61 +3989,70 @@ coded to avoid them.
@node Broken Foreign KEY, Missing Views, Missing Foreign Keys, Missing functions
-@subsubsection Reasons NOT to Use Foreign Keys constraints
+@subsubsection Why We Did Not Implement Foreign Keys
-@cindex foreign keys, reasons not to use
+@cindex foreign keys, why not implemented
-There are so many problems with foreign key constraints that we don't
-know where to start:
+Many database scholars and programmers feel very strongly that
+referential integrity should be enforced inside the database server. Indeed,
+in many cases, this approach is very helpful. However, in talking with many
+database users we have observed that foreign keys are often misused, which
+can cause severe problems. Even when used properly, it is not a
+magic solution for the referential integrity problem, although it does make
+things easier in some cases.
+
+Because of the above observations, we did not assign implementing foreign
+keys a high priority. Our user base consisted of mostly of developers who
+did not mind enforcing referential integerity inside the application code,
+and in fact, preferred to do it that way because it gave them more control.
+
+However, in the last couple of years, our user base has expanded a great deal
+and we now have many users who would like to have the enforced referential
+integrity support inside MySQL. So we will implement the foreign keys in
+the near future, although at this point we cannot provide a definite
+delivery date.
+
+Some advantages of foreign key enforcement:
@itemize @bullet
@item
-Foreign key constraints make life very complicated, because the foreign
-key definitions must be stored in a database and implementing them would
-destroy the whole ``nice approach'' of using files that can be moved,
-copied, and removed.
+Assuming proper design of the relations, foreign key constraints will make it
+more difficult for a programmer to introduce an inconsistency into the
+database
@item
-The speed impact is terrible for @code{INSERT} and @code{UPDATE}
-statements, and in this case almost all @code{FOREIGN KEY} constraint
-checks are useless because you usually insert records in the right
-tables in the right order, anyway.
+Using cascading updates and deletes can simplify the client code
@item
-There is also a need to hold locks on many more tables when updating one
-table, because the side effects can cascade through the entire database. It's
-MUCH faster to delete records from one table first and subsequently delete
-them from the other tables.
+Properly designed foreign key rules aid in documenting relations between
+tables
+@end itemize
+
+Disadvantages:
+@itemize @bullet
@item
-You can no longer restore a table by doing a full delete from the table
-and then restoring all records (from a new source or from a backup).
+MySQL does not yet support enforced referential integrity, so if your
+application depends on it, you will not be able to use it with MySQL until
+we implement this feature.
@item
-If you use foreign key constraints you can't dump and restore tables
-unless you do so in a very specific order.
+Mistakes, that are easy to make in designing key relations, can cause severe
+problems, for example, circular rules, or the wrong combination of cascading
+deletes.
@item
-It's very easy to do ``allowed'' circular definitions that make the
-tables impossible to re-create each table with a single create statement,
-even if the definition works and is usable.
+A properly written application will make sure internally that it is not
+violating referential integrity constraints before proceding with a query.
+Thus, additionaly checks on the database level will only slow down performance
+for such application.
@item
-It's very easy to overlook @code{FOREIGN KEY ... ON DELETE} rules when
-one codes an application. It's not unusual that one loses a lot of
-important information just because a wrong or misused @code{ON DELETE} rule.
+It is not uncommon for a DBA to make such a complex topology of relations that
+it becomes very difficult, and in some cases impossible to backup or restore
+individual tables.
@end itemize
-The only nice aspect of @code{FOREIGN KEY} is that it gives ODBC and some
-other client programs the ability to see how a table is connected and to use
-this to show connection diagrams and to help in building applications.
-
-MySQL will soon store @code{FOREIGN KEY} definitions so that a
-client can ask for and receive an answer about how the original
-connection was made. The current @file{.frm} file format does not have
-any place for it. At a later stage we will implement the foreign key
-constraints for application that can't easily be coded to avoid them.
-
@node Missing Views, Missing comments, Broken Foreign KEY, Missing functions
@subsubsection Views
diff --git a/vio/test-ssl b/vio/test-ssl
index fefa3fce263..0a3e73a819d 100755
--- a/vio/test-ssl
+++ b/vio/test-ssl
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