Don't allow the referencing key column from NULL TO NOT NULL
when
1) Foreign key constraint type is ON UPDATE SET NULL
2) Foreign key constraint type is ON DELETE SET NULL
3) Foreign key constraint type is UPDATE CASCADE and referenced
column declared as NULL
Don't allow the referenced key column from NOT NULL to NULL
when foreign key constraint type is UPDATE CASCADE
and referencing key columns doesn't allow NULL values
get_foreign_key_info(): InnoDB sends the information about
nullability of the foreign key fields and referenced key fields.
fk_check_column_changes(): Enforce the above rules for COPY
algorithm
innobase_check_foreign_drop_col(): Checks whether the dropped
column exists in existing foreign key relation
innobase_check_foreign_low() : Enforce the above rules for
INPLACE algorithm
dict_foreign_t::check_fk_constraint_valid(): This is used
by CREATE TABLE statement to check nullability for foreign
key relation.
The method was declared to return an unsigned integer, but it is
really a boolean (and used as such by all callers).
A secondary change is the addition of "const" and "noexcept" to this
method.
In ha_mroonga.cpp, I also added "inline" to the two helper methods of
referenced_by_foreign_key(). This allows the compiler to flatten the
method.
In the bug report MDEV-32817 it occurred that the function
row_mysql_get_table_status() is outputting a fil_space_t*
as if it were a numeric tablespace identifier.
ib_push_warning(): Remove. Let us invoke push_warning_printf() directly.
innodb_decryption_failed(): Report a decryption failure and set the
dict_table_t::file_unreadable flag. This code was being duplicated in
very many places. We return the constant value DB_DECRYPTION_FAILED
in order to avoid code duplication in the callers and to allow tail calls.
innodb_fk_error(): Report a FOREIGN KEY error.
dict_foreign_def_get(), dict_foreign_def_get_fields(): Remove.
This code was being used in dict_create_add_foreign_to_dictionary()
in an apparently uncovered code path. That ib_push_warning() call
would pass the integer i+1 instead of a pointer to NUL terminated
string ("%s"), and therefore the call should have resulted in a crash.
dict_print_info_on_foreign_key_in_create_format(),
innobase_quote_identifier(): Add const qualifiers.
row_mysql_get_table_error(): Replaces row_mysql_get_table_status().
Display no message on DB_CORRUPTION; it should be properly reported at
the SQL layer anyway.
In commit fa8a46eb68 (MDEV-33613)
the parameter innodb_lru_flush_size ceased to have any effect.
Let us declare the parameter as deprecated and additionally as
MARIADB_REMOVED_OPTION, so that there will be a warning written
to the error log in case the option is specified in the command line.
Let us also do the same for the parameter
innodb_purge_rseg_truncate_frequency
that was deprecated&ignored earlier in MDEV-32050.
Reviewed by: Debarun Banerjee
In a Sysbench oltp_update_index workload that involves 1 table,
a serious contention between the workload and the purge of history
was observed. This was the worst when the table contained only 1 record.
This turned out to be fixed by setting innodb_purge_batch_size=128,
which corresponds to the number of usable persistent rollback segments.
When we go above that, there would be contention between row_purge_poss_sec()
and the workload, typically on the clustered index page latch, sometimes
also on a secondary index page latch. It might be that with smaller
batches, trx_sys.history_size() will end up pausing all concurrent
transaction start/commit frequently enough so that purge will be able
to make some progress, so that there would be less contention on the
index page latches between purge and SQL execution.
In commit aa719b5010 (part of MDEV-32050)
the interpretation of the parameter innodb_purge_batch_size was slightly
changed. It would correspond to the maximum desired size of the
purge_sys.pages cache. Before that change, the parameter was referring to
a number of undo log pages, but the accounting might have been inaccurate.
To avoid a regression, we will reduce the default value to
innodb_purge_batch_size=127, which will also be compatible with
innodb_undo_tablespaces>1 (which will disable rollback segment 0).
Additionally, some logic in the purge and MVCC checks is simplified.
The purge tasks will make use of purge_sys.pages when accessing undo
log pages to find out if a secondary index record can be removed.
If an undo page needs to be looked up in buf_pool.page_hash, we will
merely buffer-fix it. This is correct, because the undo pages are
append-only in nature. Holding purge_sys.latch or purge_sys.end_latch
or the fact that the current thread is executing as a part of an
in-progress purge batch will prevent the contents of the undo page from
being freed and subsequently reused. The buffer-fix will prevent the
page from being evicted form the buffer pool. Thanks to this logic,
we can refer to the undo log record directly in the buffer pool page
and avoid copying the record.
buf_pool_t::page_fix(): Look up and buffer-fix a page. This is useful
for accessing undo log pages, which are append-only by nature.
There will be no need to deal with change buffer or ROW_FORMAT=COMPRESSED
in that case.
purge_sys_t::view_guard::view_guard(): Allow the type of guard to be
acquired: end_latch, latch, or no latch (in case we are a purge thread).
purge_sys_t::view_guard::get(): Read-only accessor to purge_sys.pages.
purge_sys_t::get_page(): Invoke buf_pool_t::page_fix().
row_vers_old_has_index_entry(): Replaced with row_purge_is_unsafe()
and row_undo_mod_sec_unsafe().
trx_undo_get_undo_rec(): Merged to trx_undo_prev_version_build().
row_purge_poss_sec(): Add the parameter mtr and remove redundant
or unused parameters sec_pcur, sec_mtr, is_tree. We will use the
caller's mtr object but release any acquired page latches before
returning.
btr_cur_get_page(), page_cur_get_page(): Do not invoke page_align().
row_purge_remove_sec_if_poss_leaf(): Return the value of PAGE_MAX_TRX_ID
to be checked against the page in row_purge_remove_sec_if_poss_tree().
If the secondary index page was not changed meanwhile, it will be
unnecessary to invoke row_purge_poss_sec() again.
trx_undo_prev_version_build(): Access any undo log pages using
the caller's mini-transaction object.
row_purge_vc_matches_cluster(): Moved to the only compilation unit that
needs it.
Reviewed by: Debarun Banerjee
int wsrep_thd_append_key(THD*, const wsrep_key*, int, Wsrep_service_key_type)
CREATE TABLE [SELECT|REPLACE SELECT] is CTAS and idea was that
we force ROW format. However, it was not correctly enforced
and keys were appended before wsrep transaction was started.
At THD::decide_logging_format we should force used stmt binlog
format to ROW in CTAS case and produce a warning if used
binlog format was not ROW.
At ha_innodb::update_row we should not append keys similarly
as in ha_innodb::write_row if sql_command is SQLCOM_CREATE_TABLE.
Improved error logging on ::write_row, ::update_row and ::delete_row
if wsrep key append fails.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>
Problem:
========
- After the commit ada1074bb1 (MDEV-14398)
fil_crypt_set_encrypt_tables() iterates through all tablespaces to
fill the default_encrypt tables list. This was a trigger to
encrypt or decrypt when key rotation age is set to 0. But import
tablespace does call fil_crypt_set_encrypt_tables() unnecessarily.
The motivation for the call is to signal the encryption threads.
Fix:
====
ha_innobase::discard_or_import_tablespace: Remove the
fil_crypt_set_encrypt_tables() and add the import tablespace
to the default encrypt list if necessary
(With trivial fixes by sergey@mariadb.com)
Added option fix_innodb_cardinality to optimizer_adjust_secondary_key_costs
Using fix_innodb_cardinality disables the 'divide by 2' of rec_per_key_int
in InnoDB that in effect doubles the Cardinality for secondary keys.
This has the biggest effect for indexes where a few rows has the same key
value. Using this may also cause table scans for very small tables (which
in some cases may be better than an index scan).
The user visible effect is that 'SHOW INDEX FROM table_name' will for
InnoDB show the true Cardinality (and not 2x the real value). It will
also allow the optimizer to chose a better index in some cases as the
division by 2 could have a bad effect for tables with 2-5 identical values
per key.
A few notes about using fix_innodb_cardinality:
- It has direct affect for SHOW INDEX FROM table_name. SHOW INDEX
will also update the statistics in table share.
- The effect of fix_innodb_cardinality for query plans or EXPLAIN
is only visible after first open of the table. This is why one must
do a flush tables or use SHOW INDEX for the option to take effect.
- Using fix_innodb_cardinality can thus affect all user in their query
plans if they are using the same tables.
Because of this, it is strongly recommended that one uses
optimizer_adjust_secondary_key_costs=fix_innodb_cardinality mainly
in configuration files to not cause issues for other users.
During read only mode, InnoDB doesn't allow checkpoint to happen.
So InnoDB should throw the warning when InnoDB tries to
force the checkpoint when innodb_read_only = 1 or
innodb_force_recovery = 6.
InnoDB transactions may be reused after committed:
- when taken from the transaction pool
- during a DDL operation execution
In this case wsrep flag on trx object is cleared, which may cause wrong
execution logic afterwards (wsrep-related hooks are not run).
Make trx->wsrep flag initialize from THD object only once on InnoDB transaction
start and don't change it throughout the transaction's lifetime.
The flag is reset at commit time as before.
Unconditionally set wsrep=OFF for THD objects that represent InnoDB background
threads.
Make Wsrep_schema::store_view() operate in its own transaction.
Fix streaming replication transactions' fragments rollback to not switch
THD->wsrep value during transaction's execution
(use THD->wsrep_ignore_table as a workaround).
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>
During a Sysbench oltp_point_select workload with 1 table and 400
concurrent connections, a bottleneck on dict_table_t::lock_mutex was
observed in ha_innobase::info_low().
dict_table_t::lock_latch: Replaces lock_mutex.
In ha_innobase::info_low() and several other places, we will acquire
a shared dict_table_t::lock_latch or we may elide the latch if
hardware memory transactions are available.
innobase_build_v_templ(): Remove the parameter "bool locked", and
require the caller to hold exclusive dict_table_t::lock_latch
(instead of holding an exclusive dict_sys.latch).
Tested by: Vladislav Vaintroub
Reviewed by: Vladislav Vaintroub
ha_innobase::info_low(): For HA_STATUS_VARIABLE without
HA_STATUS_VARIABLE_EXTRA, let us avoid unnecessary and costly updates
of the data_free statistics, which are only needed for SHOW TABLE STATUS.
This optimization had been enabled in
commit 247ecb7597 but not utilized until now.
Problem was that there was two non-conflicting local idle
transactions in node_1 that both inserted a key to primary key.
Then two transactions from other nodes inserted also
a key to primary key so that insert from node_2 conflicted
one of the local transactions in node_1 so that there would
be duplicate key if both are committed. For this insert
from other node tries to acquire S-lock for this record
and because this insert is high priority brute force (BF)
transaction it will kill idle local transaction.
Concurrently, second insert from node_3 conflicts the second
idle insert transaction in node_1. Again, it tries to acquire
S-lock for this record and kills idle local transaction.
At this point we have two non-conflicting high priority
transactions holding S-lock on different records in node_1.
For example like this: rec s-lock-node2-rec s-lock-node3-rec rec.
Because these high priority BF-transactions do not wait
each other insert from node3 that has later seqno compared
to insert from node2 can continue. It will try to acquire
insert intention for record it tries to insert (to avoid
duplicate key to be inserted by local transaction). Hower,
it will note that there is conflicting S-lock in same gap
between records. This will lead deadlock error as we have
defined that BF-transactions may not wait for record lock
but we can't kill conflicting BF-transaction because
it has lower seqno and it should commit first.
BF-transactions are executed concurrently because their
values to primary key are different i.e. they do not
conflict.
Galera certification will make sure that inserts from
other nodes i.e these high priority BF-transactions
can't insert duplicate keys. Local transactions naturally
can but they will be killed when BF-transaction
acquires required record locks.
Therefore, we can allow situation where there is conflicting
S-lock and insert intention lock regardless of their seqno
order and let both continue with no wait. This will lead
to situation where we need to allow BF-transaction
to wait when lock_rec_has_to_wait_in_queue is called
because this function is also called from
lock_rec_queue_validate and because lock is waiting
there would be assertion in ut_a(lock->is_gap()
|| lock_rec_has_to_wait_in_queue(cell, lock));
lock_wait_wsrep_kill
Add debug sync points for BF-transactions killing
local transaction.
wsrep_assert_no_bf_bf_wait
Print also requested lock information
lock_rec_has_to_wait
Add function to handle wsrep transaction lock wait
cases.
lock_rec_has_to_wait_wsrep
New function to handle wsrep transaction lock wait
exceptions.
lock_rec_has_to_wait_in_queue
Remove wsrep exception, in this function all
conflicting locks need to wait in queue.
Conflicts between BF and local transactions
are handled in lock_wait.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>
number of non-user tablespace.
- InnoDB only closes the user tablespace when the number of open
files exceeds innodb_open_files limit. In that case, InnoDB should
make sure that innodb_open_files value should be greater
than number of undo tablespace, system and temporary tablespace files.
In commit 99bd22605938c42d876194f2ec75b32e658f00f5 (MDEV-31558)
we wrongly thought that there would be minimal overhead for accessing
a thread-local variable mariadb_stats.
It turns out that in C++11, each access to an extern thread_local
variable requires conditionally invoking an initialization function.
In fact, the initializer expression of mariadb_stats is dynamic, and
those calls were actually unavoidable.
In C++20, one could declare constinit thread_local variables, but
the address of a thread_local variable (&mariadb_dummy_stats) is not
a compile-time constant. We did not want to declare mariadb_dummy_stats
without thread_local, because then the dummy accesses could lead to
cache line contention between threads.
mariadb_stats: Declare as __thread or __declspec(thread) so that
there will be no dynamic initialization, but zero-initialization.
mariadb_dummy_stats: Remove. It is a lesser evil to let
the environment perform zero-initialization and check if
!mariadb_stats.
Reviewed by: Sergei Petrunia
- Added a counter innodb_num_bulk_insert_operation in
INFORMATION_SCHEMA.GLOBAL_STATUS. This counter is incremented
whenever a InnoDB undergoes bulk insert operation.
- Change the innodb_instant_alter_column to atomic variable.
Correct the second parameter for strxnmov to prevent potential buffer
overflows. The second parameter must be one less than the size of the
input buffer to avoid writing past the end of the buffer.
While the second parameter is usually correct, there are exceptions
that need fixing.
This commit addresses the issue within frm_file_exists() and other
affected places.
Problem:
========
- Partition update operation enables the bulk insert for the
transaction while moving the row between partitions. This leads
to debug assert failure while removing the row from one
of the partition.
Solution:
========
- Disallow the bulk insert operation for non-insert operation
of partition table.
We have quite a few assertions
ut_a(m_prebuilt->trx == thd_to_trx(ha_thd()));
in low-level functions.
These had better be debug assertions for performance reasons.
It should suffice to check that condition in the less frequently invoked
ha_innobase::change_active_index().
convert_search_mode_to_innobase(): Return whether the mode is
unsupported, and optionally update ha_innobase::m_last_match_mode.
ha_innobase::index_read(): Only branch on find_flag once, and
simplify the error handling after invoking row_search_mvcc().
ha_innobase::rnd_pos(): Remove an assertion that is duplicating one
in ha_innobase::index_read(), which we are calling unconditionally.
ha_innobase::records_in_range(): Check only once whether
min_key, max_key are null pointers.
row_sel_convert_mysql_key_to_innobase(): Declare all parameters
except the conversion buffer pointer (buf) to be nonnull.
Reviewed by: Debarun Banerjee
Fix in this commit handles foreign key value appending into write set
so that db and table names are converted from the filepath format
to tablename format. This is compatible with key values appended from
elsewhere in the code base
There is a mtr test galera.galera_table_with_hyphen for regression testing
Reviewer: monty@mariadb.com
https://jepsen.io/analyses/mysql-8.0.34 highlights that the
transaction isolation levels in the InnoDB storage engine do not
correspond to any widely accepted definitions, such as
"Generalized Isolation Level Definitions"
https://pmg.csail.mit.edu/papers/icde00.pdf
(PL-1 = READ UNCOMMITTED, PL-2 = READ COMMITTED, PL-2.99 = REPEATABLE READ,
PL-3 = SERIALIZABLE).
Only READ UNCOMMITTED in InnoDB seems to match the above definition.
The issue is that InnoDB does not detect write/write conflicts
(Section 4.4.3, Definition 6) in the above.
It appears that as soon as we implement write/write conflict detection
(SET SESSION innodb_snapshot_isolation=ON), the default isolation level
(SET TRANSACTION ISOLATION LEVEL REPEATABLE READ) will become
Snapshot Isolation (similar to Postgres), as defined in Section 4.2 of
"A Critique of ANSI SQL Isolation Levels", MSR-TR-95-51, June 1995
https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/tr-95-51.pdf
Locking reads inside InnoDB used to read the latest committed version,
ignoring what should actually be visible to the transaction.
The added test innodb.lock_isolation illustrates this. The statement
UPDATE t SET a=3 WHERE b=2;
is executed in a transaction that was started before a read view or
a snapshot of the current transaction was created, and committed before
the current transaction attempts to execute
UPDATE t SET b=3;
If SET innodb_snapshot_isolation=ON is in effect when the second
transaction was started, the second transaction will be aborted with
the error ER_CHECKREAD. By default (innodb_snapshot_isolation=OFF),
the second transaction would execute inconsistently, displaying an
incorrect SELECT COUNT(*) FROM t in its read view.
If innodb_snapshot_isolation=ON, if an attempt to acquire a lock on a
record that does not exist in the current read view is made, an error
DB_RECORD_CHANGED (HA_ERR_RECORD_CHANGED, ER_CHECKREAD) will
be raised. This error will be treated in the same way as a deadlock:
the transaction will be rolled back.
lock_clust_rec_read_check_and_lock(): If the current transaction has
a read view where the record is not visible and
innodb_snapshot_isolation=ON, fail before trying to acquire the lock.
row_sel_build_committed_vers_for_mysql(): If innodb_snapshot_isolation=ON,
disable the "semi-consistent read" logic that had been implemented by
myself on the directions of Heikki Tuuri in order to address
https://bugs.mysql.com/bug.php?id=3300 that was motivated by a customer
wanting UPDATE to skip locked rows that do not match the WHERE condition.
It looks like my changes were included in the MySQL 5.1.5
commit ad126d90e0; at that time, employees
of Innobase Oy (a recent acquisition of Oracle) had lost write access to
the repository.
The only reason why we set innodb_snapshot_isolation=OFF by default is
backward compatibility with applications, such as the one that motivated
the implementation of "semi-consistent read" back in 2005. In a later
major release, we can default to innodb_snapshot_isolation=ON.
Thanks to Peter Alvaro, Kyle Kingsbury and Alexey Gotsman for their work
on https://github.com/jepsen-io/ and to Kyle and Alexey for explanations
and some testing of this fix.
Thanks to Vladislav Lesin for the initial test for MDEV-26643,
as well as reviewing these changes.
Starting with clang-16, MemorySanitizer appears to check that
uninitialized values not be passed by value nor returned.
Previously, it was allowed to copy uninitialized data in such cases.
get_foreign_key_info(): Remove a local variable that was passed
uninitialized to a function.
DsMrr_impl: Initialize key_buffer, because DsMrr_impl::dsmrr_init()
is reading it.
test_bind_result_ext1(): MYSQL_TYPE_LONG is 32 bits, hence we must
use a 32-bit type, such as int. sizeof(long) differs between
LP64 and LLP64 targets.
MDEV-33558 Fatal error InnoDB: Clustered record field for column x not found
This is issue is about row ID filtering used with index on virtual
column(s). We hit debug assert and crash while building the record
template in Innodb. The primary reason is that we try to force the code
path to use the ICP path. With ICP, we don't support index with virtual
column and we validate it while index condition is pushed.
Simplify the code for building template to handle both ICP and Row ID
filtering by skipping virtual columns.
The issue here is ha_innobase::get_auto_increment() could cause a
deadlock involving auto-increment lock and rollback the transaction
implicitly. For such cases, storage engines usually call
thd_mark_transaction_to_rollback() to inform SQL engine about it which
in turn takes appropriate actions and close the transaction. In innodb,
we call it while converting Innodb error code to MySQL.
However, since ::innobase_get_autoinc() returns void, we skip the call
for error code conversion and also miss marking the transaction for
rollback for deadlock error. We assert eventually while releasing a
savepoint as the transaction state is not active.
Since convert_error_code_to_mysql() is handling some generic error
handling part, like invoking the callback when needed, we should call
that function in ha_innobase::get_auto_increment() even if we don't
return the resulting mysql error code back.
MDEV-33308 CHECK TABLE is modifying .frm file even if --read-only
As noted in commit d0ef1aaf61,
MySQL as well as older versions of MariaDB server would during
ALTER TABLE ... IMPORT TABLESPACE write bogus values to the
PAGE_MAX_TRX_ID field to pages of the clustered index, instead of
letting that field remain 0.
In commit 8777458a6e this field
was repurposed for PAGE_ROOT_AUTO_INC in the clustered index root page.
To avoid trouble when upgrading from MySQL or older versions of MariaDB,
we will try to detect and correct bogus values of PAGE_ROOT_AUTO_INC
when opening a table for the first time from the SQL layer.
btr_read_autoinc_with_fallback(): Add the parameters to mysql_version,max
to indicate the TABLE_SHARE::mysql_version of the .frm file and the
maximum value allowed for the type of the AUTO_INCREMENT column.
In case the table was originally created in MySQL or an older version of
MariaDB, read also the maximum value of the AUTO_INCREMENT column from
the table and reset the PAGE_ROOT_AUTO_INC if it is above the limit.
dict_table_t::get_index(const dict_col_t &) const: Find an index that
starts with the specified column.
ha_innobase::check_for_upgrade(): Return HA_ADMIN_FAILED if InnoDB
needs upgrading but is in read-only mode. In this way, the call to
update_frm_version() will be skipped.
row_import_autoinc(): Adjust the AUTO_INCREMENT column at the end of
ALTER TABLE...IMPORT TABLESPACE. This refinement was suggested by
Debarun Banerjee.
The changes outside InnoDB were developed by Michael 'Monty' Widenius:
Added print_check_msg() service for easy reporting of check/repair messages
in ENGINE=Aria and ENGINE=InnoDB.
Fixed that CHECK TABLE do not update the .frm file under --read-only.
Added 'handler_flags' to HA_CHECK_OPT as a way for storage engines to
store state from handler::check_for_upgrade().
Reviewed by: Debarun Banerjee
lock_table_children(): A new function to lock all child tables of a table.
We will only hold dict_sys.latch while traversing
dict_table_t::referenced_set. To prevent a race condition with
std::set::erase() we will copy the pointers to the child tables to a
local vector. Once we have acquired MDL and references to all child tables,
we can safely release dict_sys.latch, wait for the locks, and finally
release the references.
dict_acquire_mdl_shared(): A new variant that takes mdl_context as a
parameter.
lock_table_for_trx(): Assert that we are not holding dict_sys.latch.
ha_innobase::truncate(): When foreign_key_checks=ON, assert that
no child tables exist (other than the current table).
In any case, we will invoke lock_table_children()
so that the child table metadata can be safely updated.
(It is possible that a child table is being created concurrently
with TRUNCATE TABLE.)
ha_innobase::delete_table(): Before and after acquiring exclusive
locks on the current table as well as all child tables,
check that FOREIGN KEY constraints will not be violated.
In this way, we can reject impossible DROP TABLE without having to
wait for locks first.
This fixes up commit 2ca1123464 (MDEV-26217)
and commit c3c53926c4 (MDEV-26554).
This follows up commit 383f77cd84
which simplified dict_table_schema_check().
Note: We can display quoted names like this:
my_snprintf(buf, sizeof buf, "%`.*s.%`s",
int(t->name.dblen()), t->name.m_name, t->name.basename());
Reason:
======
undo_space_dblwr test case fails if the first page of undo
tablespace is not flushed before restart the server. While
restarting the server, InnoDB fails to detect the first
page of undo tablespace from doublewrite buffer.
Fix:
===
Use "ib_log_checkpoint_avoid_hard" debug sync point
to avoid checkpoint and make sure to flush the
dirtied page before killing the server.
innodb_make_page_dirty(): Fails to set
srv_fil_make_page_dirty_debug variable.
The directio(3C) function on Solaris is supported on NFS and UFS
while the majority of users should be on ZFS, which is a copy-on-write
file system that implements transparent compression and therefore
cannot support unbuffered I/O.
Let us remove the call to directio() and simply treat
innodb_flush_method=O_DIRECT in the same way as the previous
default value innodb_flush_method=fsync on Solaris. Also, let us
remove some dead code around calls to os_file_set_nocache() on
platforms where fcntl(2) is not usable with O_DIRECT.
On IBM AIX, O_DIRECT is not documented for fcntl(2), only for open(2).
