Issue
====
The issue is that the info message that InnoDB prints when a table
is created with a reference which doesn't exist fills up the log as
it's printed for every insert when foreign_key_checks is disabled.
Fix
===
The fix is to display the message only if foreign_key_checks is
enabled.
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
row_update_for_mysql(): Remove the wrapper function and
rename the function from row_update_for_mysql_using_upd_graph().
Remove the unused parameter mysql_rec.
Problem was introduced with the InnoDB 5.7 merge, the code related to
avoiding extra fsync at the end of commit when binlog is enabled. The
MariaDB method for this was removed, but the replacement MySQL method
based on thd_get_durability_property() is not functional in MariaDB.
This commit reverts the offending parts of the merge and adds a test
case, to fix the problem for InnoDB. But other storage engines are
likely to have a similar problem.
when opening 10.1- table that has virtual columns:
1. don't error out if it has vcols over autoinc columns.
just issue a warning.
2. set vcol type properly
3. in innodb: use table->s->stored_fields instead of table->s->fields,
because that's what was stored in innodb data dictionary
don't use thd->query_id check in background purge threads
(it doesn't work, because thd->query_id is never incremented there)
instead use thd->open_tables directly, there can be only one table
there anyway, and this is the table opened by this purge thread.
InnoDB I/O and buffer pool interfaces and the redo log format
have been changed between MariaDB 10.1 and 10.2, and the backup
code has to be adjusted accordingly.
The code has been simplified, and many memory leaks have been fixed.
Instead of the file name xtrabackup_logfile, the file name ib_logfile0
is being used for the copy of the redo log. Unnecessary InnoDB startup and
shutdown and some unnecessary threads have been removed.
Some help was provided by Vladislav Vaintroub.
Parameters have been cleaned up and aligned with those of MariaDB 10.2.
The --dbug option has been added, so that in debug builds,
--dbug=d,ib_log can be specified to enable diagnostic messages
for processing redo log entries.
By default, innodb_doublewrite=OFF, so that --prepare works faster.
If more crash-safety for --prepare is needed, double buffering
can be enabled.
The parameter innodb_log_checksums=OFF can be used to ignore redo log
checksums in --backup.
Some messages have been cleaned up.
Unless --export is specified, Mariabackup will not deal with undo log.
The InnoDB mini-transaction redo log is not only about user-level
transactions; it is actually about mini-transactions. To avoid confusion,
call it the redo log, not transaction log.
We disable any undo log processing in --prepare.
Because MariaDB 10.2 supports indexed virtual columns, the
undo log processing would need to be able to evaluate virtual column
expressions. To reduce the amount of code dependencies, we will not
process any undo log in prepare.
This means that the --export option must be disabled for now.
This also means that the following options are redundant
and have been removed:
xtrabackup --apply-log-only
innobackupex --redo-only
In addition to disabling any undo log processing, we will disable any
further changes to data pages during --prepare, including the change
buffer merge. This means that restoring incremental backups should
reliably work even when change buffering is being used on the server.
Because of this, preparing a backup will not generate any further
redo log, and the redo log file can be safely deleted. (If the
--export option is enabled in the future, it must generate redo log
when processing undo logs and buffered changes.)
In --prepare, we cannot easily know if a partial backup was used,
especially when restoring a series of incremental backups. So, we
simply warn about any missing files, and ignore the redo log for them.
FIXME: Enable the --export option.
FIXME: Improve the handling of the MLOG_INDEX_LOAD record, and write
a test that initiates a backup while an ALGORITHM=INPLACE operation
is creating indexes or rebuilding a table. An error should be detected
when preparing the backup.
FIXME: In --incremental --prepare, xtrabackup_apply_delta() should
ensure that if FSP_SIZE is modified, the file size will be adjusted
accordingly.
The POINT data type is being treated just like any other
geometry data type in InnoDB. The fixed-length data type
DATA_POINT had been introduced in WL#6942 based on a
misunderstanding and without appropriate review.
Because of fundamental design problems (such as a
DEFAULT POINT(0 0) value secretly introduced by InnoDB),
the code was disabled in Oracle Bug#20415831 fix.
This patch removes the dead code and definitions that were
left behind by the Oracle Bug#20415831 patch.
In Mariabackup, we would want the backed-up redo log file size to be
a multiple of 512 bytes, or OS_FILE_LOG_BLOCK_SIZE. However, at startup,
InnoDB would be picky, requiring the file size to be a multiple of
innodb_page_size.
Furthermore, InnoDB would require the parameter to be a multiple of
one megabyte, while the minimum granularity is 512 bytes. Because
the data-file-oriented fil_io() API is being used for writing the
InnoDB redo log, writes will for now require innodb_log_file_size to
be a multiple of the maximum innodb_page_size (65536 bytes).
To complicate matters, InnoDB startup divided srv_log_file_size by
UNIV_PAGE_SIZE, so that initially, the unit was bytes, and later it
was innodb_page_size. We will simplify this and keep srv_log_file_size
in bytes at all times.
innobase_log_file_size: Remove. Remove some obsolete checks against
overflow on 32-bit systems. srv_log_file_size is always 64 bits, and
the maximum size 512GiB in multiples of innodb_page_size always fits
in ulint (which is 32 or 64 bits). 512GiB would be 8,388,608*64KiB or
134,217,728*4KiB.
log_init(): Remove the parameter file_size that was always passed as
srv_log_file_size.
log_set_capacity(): Add a parameter for passing the requested file size.
srv_log_file_size_requested: Declare static in srv0start.cc.
create_log_file(), create_log_files(),
innobase_start_or_create_for_mysql(): Invoke fil_node_create()
with srv_log_file_size expressed in multiples of innodb_page_size.
innobase_start_or_create_for_mysql(): Require the redo log file sizes
to be multiples of 512 bytes.
When it comes to DEFAULT values of columns, InnoDB is imposing both
unnecessary and insufficient conditions on whether ALGORITHM=INPLACE
should be allowed for ALTER TABLE.
When changing an existing column to NOT NULL, any NULL values in the
columns only get a special treatment if the column is changed to an
AUTO_INCREMENT column (which is not supported by ALGORITHM=INPLACE)
or the column type is TIMESTAMP. In all other cases, an error
must be reported for the failure to convert a NULL value to NOT NULL.
InnoDB was unnecessarily interested in whether the DEFAULT value
is not constant when altering other than TIMESTAMP columns. Also,
when changing a TIMESTAMP column to NOT NULL, InnoDB was performing
an insufficient check, and it was incorrectly allowing a constant
DEFAULT value while not being able to replace NULL values with that
constant value.
Furthermore, in ADD COLUMN, InnoDB is unnecessarily rejecting certain
nondeterministic DEFAULT expressions (depending on the session
parameters or the current time).
When the btr_search_latch was split into an array of latches
in MySQL 5.7.8 as part of the Oracle Bug#20985298 fix, the "caching"
of the latch across storage engine API calls was removed, and
the field trx->has_search_latch would only be set during a short
time frame in the execution of row_search_mvcc(), which was
formerly called row_search_for_mysql().
This means that the column
INFORMATION_SCHEMA.INNODB_TRX.TRX_ADAPTIVE_HASH_LATCHED will always
report 0. That column cannot be removed in MariaDB 10.2, but it
can be removed in future releases.
trx_t::has_search_latch: Remove.
trx_assert_no_search_latch(): Remove.
row_sel_try_search_shortcut_for_mysql(): Remove a redundant condition
on trx->has_search_latch (it was always true).
sync_check_iterate(): Make the parameter const.
sync_check_functor_t: Make the operator() const, and remove result()
and the virtual destructor. There is no need to have mutable state
in the functors.
sync_checker<bool>: Replaces dict_sync_check and btrsea_sync_check.
sync_check: Replaces btrsea_sync_check.
dict_sync_check: Instantiated from sync_checker.
sync_allowed_latches: Use std::find() directly on the array.
Remove the std::vector.
TrxInInnoDB::enter(), TrxInInnoDB::exit(): Remove obviously redundant
debug assertions on trx->in_depth, and use equality comparison against 0
because it could be more efficient on some architectures.
The sole purpose of handlerton::release_temporary_latches and its wrapper
function was to release the InnoDB adaptive hash index latch
(btr_search_latch).
When the btr_search_latch was split into an array of latches
in MySQL 5.7.8 as part of the Oracle Bug#20985298 fix, the "caching"
of the latch across storage engine API calls was removed. As part of that,
the function trx_search_latch_release_if_reserved() was changed to an
assertion and the function trx_reserve_search_latch_if_not_reserved()
was removed, and handlerton::release_temporary_latches() practically
became a no-op.
Note: MDEV-12121 replaced the function
trx_search_latch_release_if_reserved()
with the more appropriately named macro trx_assert_no_search_latch().
innodb.table_flags: Adjust the test case. Due to the MDEV-12873 fix
in 10.2, the corrupted flags for table test.td would be converted,
and a tablespace flag mismatch will occur when trying to open the file.
Remove the SHARED_SPACE flag that was erroneously introduced in
MariaDB 10.2.2, and shift the SYS_TABLES.TYPE flags back to where
they were before MariaDB 10.2.2. While doing this, ensure that
tables created with affected MariaDB versions can be loaded,
and also ensure that tables created with MySQL 5.7 using the
TABLESPACE attribute cannot be loaded.
MariaDB 10.2.2 picked the SHARED_SPACE flag from MySQL 5.7,
shifting the MariaDB 10.1 flags PAGE_COMPRESSION, PAGE_COMPRESSION_LEVEL,
ATOMIC_WRITES by one bit. The SHARED_SPACE flag would always
be written as 0 by MariaDB, because MariaDB does not support
CREATE TABLESPACE or CREATE TABLE...TABLESPACE for InnoDB.
So, instead of the bits AALLLLCxxxxxxx we would have
AALLLLC0xxxxxxx if the table was created with MariaDB 10.2.2
to 10.2.6. (AA=ATOMIC_WRITES, LLLL=PAGE_COMPRESSION_LEVEL,
C=PAGE_COMPRESSED, xxxxxxx=7 bits that were not moved.)
PAGE_COMPRESSED=NO implies LLLLC=00000. That is not a problem.
If someone created a table in MariaDB 10.2.2 or 10.2.3 with
the attribute ATOMIC_WRITES=OFF (value 2; AA=10) and without
PAGE_COMPRESSED=YES or PAGE_COMPRESSION_LEVEL, the table should be
rejected. We ignore this problem, because it should be unlikely
for anyone to specify ATOMIC_WRITES=OFF, and because 10.2.2 and
10.2.2 were not mature releases. The value ATOMIC_WRITES=ON (1)
would be interpreted as ATOMIC_WRITES=OFF, but starting with
MariaDB 10.2.4 the ATOMIC_WRITES attribute is ignored.
PAGE_COMPRESSED=YES implies that PAGE_COMPRESSION_LEVEL be between
1 and 9 and that ROW_FORMAT be COMPACT or DYNAMIC. Thus, the affected
wrong bit pattern in SYS_TABLES.TYPE is of the form AALLLL10DB00001
where D signals the presence of a DATA DIRECTORY attribute and B is 1
for ROW_FORMAT=DYNAMIC and 0 for ROW_FORMAT=COMPACT. We must interpret
this bit pattern as AALLLL1DB00001 (discarding the extraneous 0 bit).
dict_sys_tables_rec_read(): Adjust the affected bit pattern when
reading the SYS_TABLES.TYPE column. In case of invalid flags,
report both SYS_TABLES.TYPE (after possible adjustment) and
SYS_TABLES.MIX_LEN.
dict_load_table_one(): Replace an unreachable condition on
!dict_tf2_is_valid() with a debug assertion. The flags will already
have been validated by dict_sys_tables_rec_read(); if that validation
fails, dict_load_table_low() will have failed.
fil_ibd_create(): Shorten an error message about a file pre-existing.
Datafile::validate_to_dd(): Clarify an error message about tablespace
flags mismatch.
ha_innobase::open(): Remove an unnecessary warning message.
dict_tf_is_valid(): Simplify and stricten the logic. Validate the
values of PAGE_COMPRESSION. Remove error log output; let the callers
handle that.
DICT_TF_BITS: Remove ATOMIC_WRITES, PAGE_ENCRYPTION, PAGE_ENCRYPTION_KEY.
The ATOMIC_WRITES is ignored once the SYS_TABLES.TYPE has been validated;
there is no need to store it in dict_table_t::flags. The PAGE_ENCRYPTION
and PAGE_ENCRYPTION_KEY are unused since MariaDB 10.1.4 (the GA release
was 10.1.8).
DICT_TF_BIT_MASK: Remove (unused).
FSP_FLAGS_MEM_ATOMIC_WRITES: Remove (the flags are never read).
row_import_read_v1(): Display an error if dict_tf_is_valid() fails.
dict_table_t::thd: Remove. This was only used by btr_root_block_get()
for reporting decryption failures, and it was only assigned by
ha_innobase::open(), and never cleared. This could mean that if a
connection is closed, the pointer would become stale, and the server
could crash while trying to report the error. It could also mean
that an error is being reported to the wrong client. It is better
to use current_thd in this case, even though it could mean that if
the code is invoked from an InnoDB background operation, there would
be no connection to which to send the error message.
Remove dict_table_t::crypt_data and dict_table_t::page_0_read.
These fields were never read.
fil_open_single_table_tablespace(): Remove the parameter "table".
When a slow shutdown is performed soon after spawning some work for
background threads that can create or commit transactions, it is possible
that new transactions are started or committed after the purge has finished.
This is violating the specification of innodb_fast_shutdown=0, namely that
the purge must be completed. (None of the history of the recent transactions
would be purged.)
Also, it is possible that the purge threads would exit in slow shutdown
while there exist active transactions, such as recovered incomplete
transactions that are being rolled back. Thus, the slow shutdown could
fail to purge some undo log that becomes purgeable after the transaction
commit or rollback.
srv_undo_sources: A flag that indicates if undo log can be generated
or the persistent, whether by background threads or by user SQL.
Even when this flag is clear, active transactions that already exist
in the system may be committed or rolled back.
innodb_shutdown(): Renamed from innobase_shutdown_for_mysql().
Do not return an error code; the operation never fails.
Clear the srv_undo_sources flag, and also ensure that the background
DROP TABLE queue is empty.
srv_purge_should_exit(): Do not allow the purge to exit if
srv_undo_sources are active or the background DROP TABLE queue is not
empty, or in slow shutdown, if any active transactions exist
(and are being rolled back).
srv_purge_coordinator_thread(): Remove some previous workarounds
for this bug.
innobase_start_or_create_for_mysql(): Set buf_page_cleaner_is_active
and srv_dict_stats_thread_active directly. Set srv_undo_sources before
starting the purge subsystem, to prevent immediate shutdown of the purge.
Create dict_stats_thread and fts_optimize_thread immediately
after setting srv_undo_sources, so that shutdown can use this flag to
determine if these subsystems were started.
dict_stats_shutdown(): Shut down dict_stats_thread. Backported from 10.2.
srv_shutdown_table_bg_threads(): Remove (unused).
The doublewrite buffer pages must fit in the first InnoDB system
tablespace data file. The checks that were added in the initial patch
(commit 112b21da37)
were at too high level and did not cover all cases.
innodb.log_data_file_size: Test all innodb_page_size combinations.
fsp_header_init(): Never return an error. Move the change buffer creation
to the only caller that needs to do it.
btr_create(): Clean up the logic. Remove the error log messages.
buf_dblwr_create(): Try to return an error on non-fatal failure.
Check that the first data file is big enough for creating the
doublewrite buffers.
buf_dblwr_process(): Check if the doublewrite buffer is available.
Display the message only if it is available.
recv_recovery_from_checkpoint_start_func(): Remove a redundant message
about FIL_PAGE_FILE_FLUSH_LSN mismatch when crash recovery has already
been initiated.
fil_report_invalid_page_access(): Simplify the message.
fseg_create_general(): Do not emit messages to the error log.
innobase_init(): Revert the changes.
trx_rseg_create(): Refactor (no functional change).
Problem was that all doublewrite buffer pages must fit to first
system datafile.
Ported commit 27a34df7882b1f8ed283f22bf83e8bfc523cbfde
Author: Shaohua Wang <shaohua.wang@oracle.com>
Date: Wed Aug 12 15:55:19 2015 +0800
BUG#21551464 - SEGFAULT WHILE INITIALIZING DATABASE WHEN
INNODB_DATA_FILE SIZE IS SMALL
To 10.1 (with extended error printout).
btr_create(): If ibuf header page allocation fails report error and
return FIL_NULL. Similarly if root page allocation fails return a error.
dict_build_table_def_step: If fsp_header_init fails return
error code.
fsp_header_init: returns true if header initialization succeeds
and false if not.
fseg_create_general: report error if segment or page allocation fails.
innobase_init: If first datafile is smaller than 3M and could not
contain all doublewrite buffer pages report error and fail to
initialize InnoDB plugin.
row_truncate_table_for_mysql: report error if fsp header init
fails.
srv_init_abort: New function to report database initialization errors.
srv_undo_tablespaces_init, innobase_start_or_create_for_mysql: If
database initialization fails report error and abort.
trx_rseg_create: If segment header creation fails return.
Problem was that FIL_PAGE_FLUSH_LSN_OR_KEY_VERSION field that for
encrypted pages even in system datafiles should contain key_version
except very first page (0:0) is after encryption overwritten with
flush lsn.
Ported WL#7990 Repurpose FIL_PAGE_FLUSH_LSN to 10.1
The field FIL_PAGE_FLUSH_LSN_OR_KEY_VERSION is consulted during
InnoDB startup.
At startup, InnoDB reads the FIL_PAGE_FLUSH_LSN_OR_KEY_VERSION
from the first page of each file in the InnoDB system tablespace.
If there are multiple files, the minimum and maximum LSN can differ.
These numbers are passed to InnoDB startup.
Having the number in other files than the first file of the InnoDB
system tablespace is not providing much additional value. It is
conflicting with other use of the field, such as on InnoDB R-tree
index pages and encryption key_version.
This worklog will stop writing FIL_PAGE_FLUSH_LSN_OR_KEY_VERSION to
other files than the first file of the InnoDB system tablespace
(page number 0:0) when system tablespace is encrypted. If tablespace
is not encrypted we continue writing FIL_PAGE_FLUSH_LSN_OR_KEY_VERSION
to all first pages of system tablespace to avoid unnecessary
warnings on downgrade.
open_or_create_data_files(): pass only one flushed_lsn parameter
xb_load_tablespaces(): pass only one flushed_lsn parameter.
buf_page_create(): Improve comment about where
FIL_PAGE_FIL_FLUSH_LSN_OR_KEY_VERSION is set.
fil_write_flushed_lsn(): A new function, merged from
fil_write_lsn_and_arch_no_to_file() and
fil_write_flushed_lsn_to_data_files().
Only write to the first page of the system tablespace (page 0:0)
if tablespace is encrypted, or write all first pages of system
tablespace and invoke fil_flush_file_spaces(FIL_TYPE_TABLESPACE)
afterwards.
fil_read_first_page(): read flush_lsn and crypt_data only from
first datafile.
fil_open_single_table_tablespace(): Remove output of LSN, because it
was only valid for the system tablespace and the undo tablespaces, not
user tablespaces.
fil_validate_single_table_tablespace(): Remove output of LSN.
checkpoint_now_set(): Use fil_write_flushed_lsn and output
a error if operation fails.
Remove lsn variable from fsp_open_info.
recv_recovery_from_checkpoint_start(): Remove unnecessary second
flush_lsn parameter.
log_empty_and_mark_files_at_shutdown(): Use fil_writte_flushed_lsn
and output error if it fails.
open_or_create_data_files(): Pass only one flushed_lsn variable.
When MySQL 5.7 introduced fulltext parser plugins to InnoDB,
it hard-coded the plugin name "ngram" to mean something special.
Because -fsanitize=undefined was issuing warnings for the
assignment in row_merge_create_index() that the value is out of
range for Boolean, we remove this code that was not intended to
be used in MariaDB 10.2.
fts_check_token(): Remove the special logic for N-gram tokens.
Significantly reduce the amount of InnoDB, XtraDB and Mariabackup
code changes by defining pfs_os_file_t as something that is
transparently compatible with os_file_t.
This fixes warnings that were emitted when running InnoDB test
suites on a debug server that was compiled with GCC 7.1.0 using
the flags -O3 -fsanitize=undefined.
thd_requested_durability(): XtraDB can call this with trx->mysql_thd=NULL.
Remove the function in InnoDB, because it is not used there.
calc_row_difference(): Do not call memcmp(o_ptr, NULL, 0).
innobase_index_name_is_reserved(): This can be called with
key_info=NULL, num_of_keys=0.
innobase_dropping_foreign(), innobase_check_foreigns_low(),
innobase_check_foreigns(): This can be called with
drop_fk=NULL, n_drop_fk=0.
rec_convert_dtuple_to_rec_comp(): Do not invoke memcpy(end, NULL, 0).
This merge reverts commit 6ca4f693c1ce472e2b1bf7392607c2d1124b4293
from current 5.6.36 innodb.
Bug #23481444 OPTIMISER CALL ROW_SEARCH_MVCC() AND READ THE
INDEX APPLIED BY UNCOMMITTED ROW
Problem:
========
row_search_for_mysql() does whole table traversal for range query
even though the end range is passed. Whole table traversal happens
when the record is not with in transaction read view.
Solution:
=========
Convert the innodb last record of page to mysql format and compare
with end range if the traversal of row_search_mvcc() exceeds 100,
no ICP involved. If it is out of range then InnoDB can avoid the
whole table traversal. Need to refactor the code little bit to
make it compile.
Reviewed-by: Jimmy Yang <jimmy.yang@oracle.com>
Reviewed-by: Knut Hatlen <knut.hatlen@oracle.com>
Reviewed-by: Dmitry Shulga <dmitry.shulga@oracle.com>
RB: 14660
Do not silence uncertain cases, or fix any bugs.
The only functional change should be that ha_federated::extra()
is not calling DBUG_PRINT to report an unhandled case for
HA_EXTRA_PREPARE_FOR_DROP.
Do not silence uncertain cases, or fix any bugs.
The only functional change should be that ha_federated::extra()
is not calling DBUG_PRINT to report an unhandled case for
HA_EXTRA_PREPARE_FOR_DROP.
Given the OK macro used in innodb does a DBUG_RETURN(1) on expression failure
the innodb implementation has a number of errors in i_s.cc.
We introduce a new macro BREAK_IF that replaces some use of the OK macro.
Also, do some other cleanup detailed below.
When invoking Field::store() on integers, always pass the parameter
is_unsigned=true to avoid an unnecessary conversion to double.
i_s_fts_deleted_generic_fill(), i_s_fts_config_fill():
Use the BREAK_IF macro instead of OK.
i_s_fts_index_cache_fill_one_index(), i_s_fts_index_table_fill_one_index():
Add a parameter for conv_string, and let the caller allocate that buffer.
i_s_fts_index_cache_fill(): Check the return status of
i_s_fts_index_cache_fill_one_index().
i_s_fts_index_table_fill(): Check the return status of
i_s_fts_index_table_fill_one_index().
i_s_fts_index_table_fill_one_fetch(): Always let the caller invoke
i_s_fts_index_table_free_one_fetch().
i_s_innodb_buffer_page_fill(), i_s_innodb_buf_page_lru_fill():
Do release dict_sys->mutex if filling the buffers fails.
i_s_innodb_buf_page_lru_fill(): Also display the value
INFORMATION_SCHEMA.INNODB_BUFFER_PAGE.PAGE_IO_FIX='IO_PIN'
when a block is in that state. Remove the unnecessary variable 'heap'.
TrxInInnoDB should be constructed to track if a transaction is executing
inside InnoDB code i.e. it is like a gate between Server and InnoDB
::rnd_next() is called from Server and thus construct TrxInInnoDB
also there.
Applied suggested clean-up to TrxInInnoDB class functions enter()
and exit(). Note that exactly original did not work for enter().
The latest attempted fix for
MDEV-11802 InnoDB purge fails to start when there is work to do
is not complete.
For now, work around the issue by making SHOW ENGINE INNODB STATUS
call srv_wake_purge_thread_if_not_active() to wake up the purge.
Use uint32_t for the encryption key_id.
When filling unsigned integer values into INFORMATION_SCHEMA tables,
use the method Field::store(longlong, bool unsigned)
instead of using Field::store(double).
Fix also some miscellanous type mismatch related to ulint (size_t).
Added a new file ha_xtradb.h where XtraDB parameters are defined. This
file is included in two places to avoid too intrusive change to
ha_innodb.cc that would make future merges harder.
innodb_show_locks_held and innodb_show_verbose_locks should be
implemented (but on different commit).
ha_innobase::check_if_supported_inplace_alter(): For now, reject
ALGORITHM=INPLACE when a non-constant DEFAULT expression is specified
for ADD COLUMN or for changing a NULL column to NOT NULL.
Later, we should evaluate the non-constant column values in these cases.
