MDEV-21652 Foreign key migration from old version
== fk_check_legacy_storage(), fk_upgrade_legacy_storage() ==
fk_check_legacy_storage() checks whether upgrade is required for the
given table name by looking SYS_FOREIGN table for corresponding record
existence.
fk_upgrade_legacy_storage() does the upgrade routine which includes
getting the foreign keys from SYS_FOREIGN[_COLS], updating the
foreign/referenced shares as well as their FRM files, deleting the
records from SYS_FOREIGN[_COLS] tables.
Both routines utilize the internal SQL for SYS_FOREIGN[_COLS]
processing.
== Upgrade foreign keys via backoff action ==
When table is opened fk_check_legacy_storage() detects whether upgrade
is required and HA_ERR_FK_UPGRADE is returned to SQL layer which then
handles this error by backoff action from Open_table_context where
table is opened again with HA_OPEN_FOR_REPAIR flag which indicates
that fk_upgrade_legacy_storage() is required. After
fk_upgrade_legacy_storage() is done fk_check_legacy_storage() is
checked again to ensure that SYS_FOREIGN[_COLS] are empty for the
given table.
== Check foreign/referenced indexes existence ==
fk_upgrade_legacy_storage() via fk_upgrade_push_fk() fails if there
are no indexes in foreign/referenced tables for the given data
acquired from SYS_FOREIGN[_COLS].
== Internal SQL: select into both func and vars extension ==
fk_upgrade_legacy_storage() utilizes syntax extension in internal SQL:
FETCH c INTO fk_upgrade_create_fk() fk_id, unused;
Thus the data is fetched into both fk_upgrade_create_fk() function and
fk_id variable.
== Rename table, rename column, drop table, drop column handling ==
When foreign table is opened it is automatically upgraded by backoff
action. But if the referenced table is altered or dropped first there
is no chance for the foreign table to get the correct data. So the
SYS_FOREIGN_[COLS] must be kept in sync with the above DDL operations
in respect of referenced names. DROP TABLE for the referenced table is
disabled as usual. DROP TABLE, DROP COLUMN relied in 10.5 on
dict_foreign_t cached data for the referenced tables. Now there is no
such possibility for the legacy data so we have to look at
SYS_FOREIGN_[COLS] directly.
== Reverted some SYS_FOREIGN(_COLS) routines ==
Rename table and rename column handling was done in sync with
SYS_FOREIGN_[COLS] in 10.5. To retain the above DDL consistency for
the referenced tables we still use that old synchronization code.
== ALGORITHM=COPY handling ==
Since we cannot faingrain ALGORITHM=COPY in innobase handler it is
disabled for the referenced tables unless the foreign tables are upgraded.
The check is done in create_table_info_t::create_table() and is
equivalent to DROP TABLE check as we are actually dropping the old
table after the copy routine is done.
== WITH_INNODB_LEGACY_FOREIGN_STORAGE macro ==
Every SYS_FOREIGN_[COLS] handling is wrapped inside
WITH_INNODB_LEGACY_FOREIGN_STORAGE compilation macro. When this macro
is disabled the foreign key upgrade is not possible. Future versions
will obsolete the upgrade completely.
== innodb_eval_sql debug interface ==
Test cases must fill SYS_FOREIGN_[COLS] with data. This is done with
setting the new innodb_eval_sql debug variable. The value of that
variable is processed by que_eval_sql().
== Some syntax error-friendly parser handling ==
que_eval_sql() was unfriendly on syntax errors: it just failed with
SIGABRT exception. To keep the server alive some frequent syntax
errors are now returned as DB_ERROR from que_eval_sql().
MDEV-21052 InnoDB foreign key refactoring for TABLE_SHARE::foreign_keys
Refactor dict_load_foreigns() for synchronising TABLE_SHARE foreign
data with dict_table_t cache.
Remove a number of routines working with SYS_FOREIGNS and
SYS_FOREIGN_COLS. innobase_update_foreign_try() is now used solely for
ER_FK_INCORRECT_OPTION check.
Prelock parent tables as well as child tables. This is done for the
case when parent table doesn't know about its children when they
created before parent with foreign_key_checks=0. Opening the parent
table initiates fk_resolve_referenced_keys() which updates its
referenced_keys. Due to CREATE TABLE doesn't not know about "illegal"
children it can not check for foreign consistency. F.ex. this would
succeed:
set foreign_key_checks= 0;
create table child (fk int references parent (id)) engine=innodb;
set foreign_key_checks= 1;
create table parent (id bigint primary key) engine=innodb;
In the above case dict_load_foreigns() deduces which tables are
unknown to opened parent (tables_missing) and reloads their foreign
data via recursion. Infinite recursion is not possible via test case:
a table cannot be "parent after child" and "child before parent"
simultaneously. Though infinite recursion is possible via malicously
crafted FRM file, there is no protection from that at InnoDB level but
there is protection at SQL level: thd->fk_circular_check.
Later though it would not allow DML on child as well as on parent (see
innodb.foreign_key MDEV-10083). So this is pretty acceptable:
foreign_key_checks is unnormal setting, checking parent on CREATE
TABLE would impose all frms scanning which is not acceptable.
ha_innobase::open() then synchronizes these referenced_keys with its
referenced_set cache by calling dict_load_foreigns().
Disable self-references on same column. The Bug 12902967 restricted
them on some condition of "same column/index" (see
innodb_bug12902967.test), though such self-references were not
completely disabled (see other self-ref cases changed in this
patch). It is not clear why they worked if they are "self-refs on same
column/index".
MDEV-20865 Store foreign key info in TABLE_SHARE
1. Access foreign keys via TABLE_SHARE::foreign_keys and
TABLE_SHARE::referenced_keys;
foreign_keys and referenced_keys are objects in TABLE_SHARE.
2. Remove handler FK interface:
- get_foreign_key_list()
- get_parent_foreign_key_list()
- referenced_by_foreign_key()
3. Invalidate referenced shares on:
- RENAME TABLE
- DROP TABLE
- RENAME COLUMN
- ADD FOREIGN KEY
When foreign table is created or altered by the above operations all
referenced shares are closed. This blocks the operation while any
referenced shares are used (when at least one its TABLE instance is
locked).
4. Update referenced shares on:
- CREATE TABLE
On CREATE TABLE add items to referenced_keys of referenced shares.
5. Invalidate foreign shares on:
- RENAME TABLE
- RENAME COLUMN
The above-mentioned blocking takes effect.
6. Debug check foreign/referenced shares on:
- FLUSH TABLE
7. Temporary change until MDEV-21051:
InnoDB fill foreign key info at handler open().
On first TABLE open FK info is loaded from storage engine into
TABLE_SHARE. All referenced shares (if any exist) are closed. This
leads to blocking of first time foreign table open while referenced
tables are used.
Restore states of referenced shares in case of errors.
FOREIGN_KEY_INFO refactored to FK_info holding Lex_cstring
(MDEV-21311) Converge Foreign_key and supplemental generated Key together
mysql_prepare_create_table() does data validation and such utilities
as automatic name generation. But it does that only for indexes and
ignores Foreign_key objects. Now as Foreign_key data needs to be
stored in FRM files as well this processing must be done for them like
for any other Key objects.
Replace Key::FOREIGN_KEY type with Key::foreign flag of type
Key::MULTIPLE and Key::generated set to true. Construct one object
with Key::foreign == true instead of two objects of type
Key::FOREIGN_KEY and Key::MULTIPLE.
(MDEV-21051) datadict refactorings
- Move read_extra2() to datadict.cc
- Refactored extra2_fields to Extra2_info
- build_frm_image() readability
(MDEV-21051) build_table_shadow_filename() refactoring
mysql_prepare_alter_table() leaks fixes
(MDEV-21051) amend system tables locking restriction
Table mysql.help_relation has foreign key to mysql.help_keyword. On
bootstrap when help_relation is opened, it preopens help_keyword for
READ and fails in lock_tables_check().
If system table is opened for write then fk references are opened for
write.
Related to: Bug#25422, WL#3984
Tests: main.lock
(MDEV-21051) Store and read foreign key info into/from FRM files
1. Introduce Foreign_key_io class which creates/parses binary stream
containing foreign key structures. Referenced tables store there only
hints about foreign tables (their db and name), they restore full info
from the corresponding tables.
Foreign_key_io is stored under new EXTRA2_FOREIGN_KEY_INFO field in
extra2 section of FRM file.
2. Modify mysql_prepare_create_table() to generate names for foreign
keys. Until InnoDB storage of foreign keys is removed, FK names must
be unique across the database: the FK name must be based on table
name.
3. Keep stored data in sync on DDL changes. Referenced tables update
their foreign hints after following operations on foreign tables:
- RENAME TABLE
- DROP TABLE
- CREATE TABLE
- ADD FOREIGN KEY
- DROP FOREIGN KEY
Foreign tables update their foreign info after following operations on
referenced tables:
- RENAME TABLE
- RENAME COLUMN
4. To achieve 3. there must be ability to rewrite extra2 section of
FRM file without full reparse. FRM binary is built from primary
structures like HA_CREATE_INFO and cannot be built from TABLE_SHARE.
Use shadow write and rename like fast_alter_partition_table() does.
Create table workflow:
1. Foreign_key is constructed in parser, placed into alter_info->key_list;
2. mysql_prepare_create_table() translates them to FK_info, assigns
foreign_id if needed;
3. build_frm_image() writes two FK_info lists into FRM's extra2
section, for referenced keys it stores only table names (hints);
4. init_from_binary_frm_image() parses extra2 section and fills
foreign_keys and referenced_keys of TABLE_SHARE.
It restores referenced_keys by reading hint list of table names,
opening corresponding shares and restoring FK_info from their
foreign_keys. Hints resolution is done only when initializing
non-temporary shares. Usually temporary share has different
(temporary) name and it is impossible to resolve foreign keys by that
name (as we identify them by both foreign and referenced table
names). Another not unimportant reason is performance: this saves
spare share acquisitions.
Alter table workflow:
1. Foreign_key is constructed in parser, placed into
alter_info->key_list;
2. mysql_prepare_alter_table() prepares action lists and share list of
foreigns/references;
3. mysql_prepare_alter_table() locks list of foreigns/references by
MDL_INTENTION_EXCLUSIVE, acquires shares;
4. prepare_create_table() converts key_list into FK_list, assigns
foreign_id;
5. shadow FRM of altered table is created;
6. data is copied;
7. altered table is locked by MDL_EXCLUSIVE;
8. fk_handle_alter() processes action lists, creates FK backups,
modifies shares, writes shadow FRMs;
9. altered table is closed;
10. shadow FRMs are installed;
11. altered table is renamed, FRM backup deleted;
12. (TBD in MDEV-21053) shadow FRMs installation log closed, backups deleted;
On FK backup system:
In case of failed DDL operation all shares that was modified must be
restored into original state. This is done by FK_ddl_backup (CREATE,
DROP), FK_rename_backup (RENAME), FK_alter_backup (ALTER).
On STL usage:
STL is used for utility not performance-critical algorithms, core
structures hold native List. A wrapper was made to convert STL
exception into bool error status or NULL value.
