Problem:
========
- InnoDB reads the length of the variable length field wrongly
while applying the modification log of instant table.
Solution:
========
rec_init_offsets_comp_ordinary(): For the temporary instant
file record, InnoDB should read the length of the variable length
field from the record itself.
In any test that uses wait_all_purged.inc, ensure that InnoDB tables
will be created without persistent statistics.
This is a follow-up to commit cd04673a17
after a similar failure was observed in the innodb_zip.blob test.
The motivation of introducing the parameter
innodb_purge_rseg_truncate_frequency in
mysql/mysql-server@28bbd66ea5 and
mysql/mysql-server@8fc2120fed
seems to have been to avoid stalls due to freeing undo log pages
or truncating undo log tablespaces. In MariaDB Server,
innodb_undo_log_truncate=ON should be a much lighter operation
than in MySQL, because it will not involve any log checkpoint.
Another source of performance stalls should be
trx_purge_truncate_rseg_history(), which is shrinking the history list
by freeing the undo log pages whose undo records have been purged.
To alleviate that, we will introduce a purge_truncation_task that will
offload this from the purge_coordinator_task. In that way, the next
innodb_purge_batch_size pages may be parsed and purged while the pages
from the previous batch are being freed and the history list being shrunk.
The processing of innodb_undo_log_truncate=ON will still remain the
responsibility of the purge_coordinator_task.
purge_coordinator_state::count: Remove. We will ignore
innodb_purge_rseg_truncate_frequency, and act as if it had been
set to 1 (the maximum shrinking frequency).
purge_coordinator_state::do_purge(): Invoke an asynchronous task
purge_truncation_callback() to free the undo log pages.
purge_sys_t::iterator::free_history(): Free those undo log pages
that have been processed. This used to be a part of
trx_purge_truncate_history().
purge_sys_t::clone_end_view(): Take a new value of purge_sys.head
as a parameter, so that it will be updated while holding exclusive
purge_sys.latch. This is needed for race-free access to the field
in purge_truncation_callback().
Reviewed by: Vladislav Lesin
trx_t::commit_empty(): A special case of transaction "commit" when
the transaction was actually rolled back or the persistent undo log
is empty. In this case, we need to change the undo log header state to
TRX_UNDO_CACHED and move the undo log from rseg->undo_list to
rseg->undo_cached for fast reuse. Furthermore, unless this is the only
undo log record in the page, we will remove the record and rewind
TRX_UNDO_PAGE_START, TRX_UNDO_PAGE_FREE, TRX_UNDO_LAST_LOG.
We must also ensure that the system-wide transaction identifier
will be persisted up to this->id, so that there will not be warnings or
errors due to a PAGE_MAX_TRX_ID being too large. We might have modified
secondary index pages before being rolled back, and any changes of
PAGE_MAX_TRX_ID are never rolled back.
Even though it is not going to be written persistently anywhere,
we will invoke trx_sys.assign_new_trx_no(this), so that in the test
innodb.instant_alter everything will be purged as expected.
trx_t::write_serialisation_history(): Renamed from
trx_write_serialisation_history(). If there is no undo log,
invoke commit_empty().
trx_purge_add_undo_to_history(): Simplify an assertion and remove a
comment. This function will not be invoked on an empty undo log anymore.
trx_undo_header_create(): Add a debug assertion.
trx_undo_mem_create_at_db_start(): Remove a duplicated assignment.
Reviewed by: Vladislav Lesin
Tested by: Matthias Leich
purge_sys_t::sees(): Wrapper for view.sees().
trx_purge_truncate_history(): Invoke purge_sys.sees() instead of
comparing to head.trx_no, to determine if undo pages can be safely freed.
The test innodb.cursor-restore-locking was adjusted by Vladislav Lesin,
as was the the debug instrumentation in row_purge_del_mark().
Reviewed by: Vladislav Lesin
- InnoDB DDL results in `Duplicate entry' if concurrent DML throws
duplicate key error. The following scenario explains the problem
connection con1:
ALTER TABLE t1 FORCE;
connection con2:
INSERT INTO t1(pk, uk) VALUES (2, 2), (3, 2);
In connection con2, InnoDB throws the 'DUPLICATE KEY' error because
of unique index. Alter operation will throw the error when applying
the concurrent DML log.
- Inserting the duplicate key for unique index logs the insert
operation for online ALTER TABLE. When insertion fails,
transaction does rollback and it leads to logging of
delete operation for online ALTER TABLE.
While applying the insert log entries, alter operation
encounters 'DUPLICATE KEY' error.
- To avoid the above fake duplicate scenario, InnoDB should
not write any log for online ALTER TABLE before DML transaction
commit.
- User thread which does DML can apply the online log if
InnoDB ran out of online log and index is marked as completed.
Set online log error if apply phase encountered any error.
It can also clear all other indexes log, marks the newly
added indexes as corrupted.
- Removed the old online code which was a part of DML operations
commit_inplace_alter_table() : Does apply the online log
for the last batch of secondary index log and does frees
the log for the completed index.
trx_t::apply_online_log: Set to true while writing the undo
log if the modified table has active DDL
trx_t::apply_log(): Apply the DML changes to online DDL tables
dict_table_t::is_active_ddl(): Returns true if the table
has an active DDL
dict_index_t::online_log_make_dummy(): Assign dummy value
for clustered index online log to indicate the secondary
indexes are being rebuild.
dict_index_t::online_log_is_dummy(): Check whether the online
log has dummy value
ha_innobase_inplace_ctx::log_failure(): Handle the apply log
failure for online DDL transaction
row_log_mark_other_online_index_abort(): Clear out all other
online index log after encountering the error during
row_log_apply()
row_log_get_error(): Get the error happened during row_log_apply()
row_log_online_op(): Does apply the online log if index is
completed and ran out of memory. Returns false if apply log fails
UndorecApplier: Introduced a class to maintain the undo log
record, latched undo buffer page, parse the undo log record,
maintain the undo record type, info bits and update vector
UndorecApplier::get_old_rec(): Get the correct version of the
clustered index record that was modified by the current undo
log record
UndorecApplier::clear_undo_rec(): Clear the undo log related
information after applying the undo log record
UndorecApplier::log_update(): Handle the update, delete undo
log and apply it on online indexes
UndorecApplier::log_insert(): Handle the insert undo log
and apply it on online indexes
UndorecApplier::is_same(): Check whether the given roll pointer
is generated by the current undo log record information
trx_t::rollback_low(): Set apply_online_log for the transaction
after partially rollbacked transaction has any active DDL
prepare_inplace_alter_table_dict(): After allocating the online
log, InnoDB does create fulltext common tables. Fulltext index
doesn't allow the index to be online. So removed the dead
code of online log removal
Thanks to Marko Mäkelä for providing the initial prototype and
Matthias Leich for testing the issue patiently.
- Server incorrectly downgrading the MDL after prepare phase when
table is empty. mdl_exclusive_after_prepare is being set in
prepare phase only. But mdl_exclusive_after_prepare condition was
misplaced and checked before prepare phase by
commit d270525dfd and it is now
changed to check after prepare phase.
- main.innodb_mysql_sync test case was changed to avoid locking
optimization when table is empty.
MDEV-23805 simplified the treatment of empty tables during ALTER TABLE,
which could prevent the scenarios that were previously reported and
fixed as MDEV-16131 and MDEV-24730.
With the MDEV-23805 fix, the statement
SET DEBUG_SYNC = 'now WAIT_FOR copied';
could occasionally time out, depending on timing.
Apparently, there was a race condition where purge could resume
(and empty the table) before ALTER TABLE got the chance to execute.
We must prevent the purge of history from running before
ALTER TABLE has started executing.
- In ha_innobase::prepare_inplace_alter_table(), InnoDB should
check whether the table is empty. If the table is empty then
server should avoid downgrading the MDL after prepare phase.
It is more like instant alter, does change only in dicationary
and metadata.
- Changed few debug test case to make non-empty DDL table
In other ROW_FORMAT than REDUNDANT, the InnoDB record header
size calculation depends on dict_index_t::n_core_null_bytes.
In ROW_FORMAT=REDUNDANT, the record header always is 6 bytes
plus n_fields or 2*n_fields bytes, depending on the maximum
record size. But, during online ALTER TABLE, the log records
in the temporary file always use a format similar to
ROW_FORMAT=DYNAMIC, even omitting the 5-byte fixed-length part
of the header.
While creating a temporary file record for a ROW_FORMAT=REDUNDANT
table, InnoDB must refer to dict_index_t::n_nullable.
The field dict_index_t::n_core_null_bytes is only valid for
other than ROW_FORMAT=REDUNDANT tables.
The bug does not affect MariaDB 10.3, because only
commit 7a27db778e (MDEV-15563)
allowed an ALGORITHM=INSTANT change of a NOT NULL column to
NULL in a ROW_FORMAT=REDUNDANT table.
The fix was developed by Thirunarayanan Balathandayuthapani
and tested by Matthias Leich. The test case was simplified by me.
Between btr_pcur_store_position() and btr_pcur_restore_position()
it is possible that purge empties a table and enlarges
index->n_core_fields and index->n_core_null_bytes.
Therefore, we must cache index->n_core_fields in
btr_pcur_t::old_n_core_fields so that btr_pcur_t::old_rec can be
parsed correctly.
Unfortunately, this is a huge change, because we will replace
"bool leaf" parameters with "ulint n_core"
(passing index->n_core_fields, or 0 for non-leaf pages).
For special cases where we know that index->is_instant() cannot hold,
we may also pass index->n_fields.
In commit eaeb8ec4b8 (MDEV-24653)
an incorrect debug assertion was introduced.
btr_pcur_store_position(): If the only record in the page is the
instant ALTER TABLE metadata record, we cannot expect there to be
a successor page. The situation could be improved by MDEV-24673 later.
Online log for insert operation of redundant table fails with
index->is_instant() assert. Purge can reset the n_core_fields when
alter is waiting to upgrade MDL for commit phase of DDL. In the
meantime, any insert DML tries to log the operation fails with
index is not being instant.
row_log_get_n_core_fields(): Get the n_core_fields of online log
for the given index.
rec_get_converted_size_comp_prefix_low(): Use n_core_fields of online
log when InnoDB calculates the size of data tuple during redundant
row format table rebuild.
rec_convert_dtuple_to_rec_comp(): Use n_core_fields of online log
when InnoDB does the conversion of data tuple to record during
redudant row format table rebuild.
- Adding the test case which has more than 129 instant columns.
We may end up with an empty leaf page (containing only an ADD COLUMN
metadata record) that is not the root page.
innobase_add_instant_try(): Disable an optimization for a non-canonical
empty table that contains a metadata record somewhere else than in
the root page.
btr_pcur_store_position(): Tolerate a non-canonical empty table.
btr_discard_only_page_on_level(): Attempt to read the MDEV-15562 metadata
record from the leaf page, not the root page. In the root, the leftmost
(in this case, the only) node pointer would look like a metadata record.
This corruption bug was introduced in
commit 0e5a4ac253 (MDEV-15562).
The scenario is rare: a column was dropped instantly or the order of
columns was changed instantly, and then the table became empty in such
a way that in the last step, the root page had one child page.
Normally, a non-leaf B-tree page would always contain at least 2 children.
This is a race condition where a table on which a 10.3-style
instant ADD COLUMN is emptied during the execution of
ALTER TABLE ... DROP COLUMN ..., DROP INDEX ..., ALGORITHM=NOCOPY.
In commit 2c4844c9e7 the
function instant_metadata_lock() would prevent this race condition.
But, it would also hold a page latch on the leftmost leaf page of
clustered index for the duration of a possible DROP INDEX operation.
The race could be fixed by restoring the function
instant_metadata_lock() that was removed in
commit ea37b14409
but it would be more future-proof to prevent the
dict_index_t::clear_instant_add() call from being issued at all.
We at some point support DROP COLUMN ..., ADD INDEX ..., ALGORITHM=NOCOPY
and that would spend a non-trivial amount of
execution time in ha_innobase::inplace_alter(),
making a server hang possible. Currently this is not supported
and our added test case will notice when the support is introduced.
dict_index_t::must_avoid_clear_instant_add(): Determine if
a call to clear_instant_add() must be avoided.
btr_discard_only_page_on_level(): Preserve the metadata record
if must_avoid_clear_instant_add() holds.
btr_cur_optimistic_delete_func(), btr_cur_pessimistic_delete():
Do not remove the metadata record even if the table becomes empty
but must_avoid_clear_instant_add() holds.
btr_pcur_store_position(): Relax a debug assertion.
This is joint work with Thirunarayanan Balathandayuthapani.
row_log_table_get_pk_old_col(): For replacing a NULL value for a
column of the being-added primary key, look up the correct
default value, even if columns had been instantly reordered or
dropped earlier. This ought to have been broken ever since
commit 0e5a4ac253 (MDEV-15562).
row_undo_ins_remove_clust_rec(): When rolling back the insert
of a metadata record, also reset the root page state within the
same mini-transaction.
dict_table_t::rollback_instant(): Do not allow index->n_core_fields
to be larger than index->n_fields. This logic exists in the 10.3
branch but was incorrectly removed as part of MDEV-15562 in 10.4.0.
Allow ADD COLUMN anywhere in a table, not only adding as the
last column.
Allow instant DROP COLUMN and instant changing the order of columns.
The added columns will always be added last in clustered index records.
In new records, instantly dropped columns will be stored as NULL or
empty when possible.
Information about dropped and reordered columns will be written in
a metadata BLOB (mblob), which is stored before the first 'user' field
in the hidden metadata record at the start of the clustered index.
The presence of mblob is indicated by setting the delete-mark flag in
the metadata record.
The metadata BLOB stores the number of clustered index fields,
followed by an array of column information for each field.
For dropped columns, we store the NOT NULL flag, the fixed length,
and for variable-length columns, whether the maximum length exceeded
255 bytes. For non-dropped columns, we store the column position.
Unlike with MDEV-11369, when a table becomes empty, it cannot
be converted back to the canonical format. The reason for this is
that other threads may hold cached objects such as
row_prebuilt_t::ins_node that could refer to dropped or reordered
index fields.
For instant DROP COLUMN and ROW_FORMAT=COMPACT or ROW_FORMAT=DYNAMIC,
we must store the n_core_null_bytes in the root page, so that the
chain of node pointer records can be followed in order to reach the
leftmost leaf page where the metadata record is located.
If the mblob is present, we will zero-initialize the strings
"infimum" and "supremum" in the root page, and use the last byte of
"supremum" for storing the number of null bytes (which are allocated
but useless on node pointer pages). This is necessary for
btr_cur_instant_init_metadata() to be able to navigate to the mblob.
If the PRIMARY KEY contains any variable-length column and some
nullable columns were instantly dropped, the dict_index_t::n_nullable
in the data dictionary could be smaller than it actually is in the
non-leaf pages. Because of this, the non-leaf pages could use more
bytes for the null flags than the data dictionary expects, and we
could be reading the lengths of the variable-length columns from the
wrong offset, and thus reading the child page number from wrong place.
This is the result of two design mistakes that involve unnecessary
storage of data: First, it is nonsense to store any data fields for
the leftmost node pointer records, because the comparisons would be
resolved by the MIN_REC_FLAG alone. Second, there cannot be any null
fields in the clustered index node pointer fields, but we nevertheless
reserve space for all the null flags.
Limitations (future work):
MDEV-17459 Allow instant ALTER TABLE even if FULLTEXT INDEX exists
MDEV-17468 Avoid table rebuild on operations on generated columns
MDEV-17494 Refuse ALGORITHM=INSTANT when the row size is too large
btr_page_reorganize_low(): Preserve any metadata in the root page.
Call lock_move_reorganize_page() only after restoring the "infimum"
and "supremum" records, to avoid a memcmp() assertion failure.
dict_col_t::DROPPED: Magic value for dict_col_t::ind.
dict_col_t::clear_instant(): Renamed from dict_col_t::remove_instant().
Do not assert that the column was instantly added, because we
sometimes call this unconditionally for all columns.
Convert an instantly added column to a "core column". The old name
remove_instant() could be mistaken to refer to "instant DROP COLUMN".
dict_col_t::is_added(): Rename from dict_col_t::is_instant().
dtype_t::metadata_blob_init(): Initialize the mblob data type.
dtuple_t::is_metadata(), dtuple_t::is_alter_metadata(),
upd_t::is_metadata(), upd_t::is_alter_metadata(): Check if info_bits
refer to a metadata record.
dict_table_t::instant: Metadata about dropped or reordered columns.
dict_table_t::prepare_instant(): Prepare
ha_innobase_inplace_ctx::instant_table for instant ALTER TABLE.
innobase_instant_try() will pass this to dict_table_t::instant_column().
On rollback, dict_table_t::rollback_instant() will be called.
dict_table_t::instant_column(): Renamed from instant_add_column().
Add the parameter col_map so that columns can be reordered.
Copy and adjust v_cols[] as well.
dict_table_t::find(): Find an old column based on a new column number.
dict_table_t::serialise_columns(), dict_table_t::deserialise_columns():
Convert the mblob.
dict_index_t::instant_metadata(): Create the metadata record
for instant ALTER TABLE. Invoke dict_table_t::serialise_columns().
dict_index_t::reconstruct_fields(): Invoked by
dict_table_t::deserialise_columns().
dict_index_t::clear_instant_alter(): Move the fields for the
dropped columns to the end, and sort the surviving index fields
in ascending order of column position.
ha_innobase::check_if_supported_inplace_alter(): Do not allow
adding a FTS_DOC_ID column if a hidden FTS_DOC_ID column exists
due to FULLTEXT INDEX. (This always required ALGORITHM=COPY.)
instant_alter_column_possible(): Add a parameter for InnoDB table,
to check for additional conditions, such as the maximum number of
index fields.
ha_innobase_inplace_ctx::first_alter_pos: The first column whose position
is affected by instant ADD, DROP, or changing the order of columns.
innobase_build_col_map(): Skip added virtual columns.
prepare_inplace_add_virtual(): Correctly compute num_to_add_vcol.
Remove some unnecessary code. Note that the call to
innodb_base_col_setup() should be executed later.
commit_try_norebuild(): If ctx->is_instant(), let the virtual
columns be added or dropped by innobase_instant_try().
innobase_instant_try(): Fill in a zero default value for the
hidden column FTS_DOC_ID (to reduce the work needed in MDEV-17459).
If any columns were dropped or reordered (or added not last),
delete any SYS_COLUMNS records for the following columns, and
insert SYS_COLUMNS records for all subsequent stored columns as well
as for all virtual columns. If any virtual column is dropped, rewrite
all virtual column metadata. Use a shortcut only for adding
virtual columns. This is because innobase_drop_virtual_try()
assumes that the dropped virtual columns still exist in ctx->old_table.
innodb_update_cols(): Renamed from innodb_update_n_cols().
innobase_add_one_virtual(), innobase_insert_sys_virtual(): Change
the return type to bool, and invoke my_error() when detecting an error.
innodb_insert_sys_columns(): Insert a record into SYS_COLUMNS.
Refactored from innobase_add_one_virtual() and innobase_instant_add_col().
innobase_instant_add_col(): Replace the parameter dfield with type.
innobase_instant_drop_cols(): Drop matching columns from SYS_COLUMNS
and all columns from SYS_VIRTUAL.
innobase_add_virtual_try(), innobase_drop_virtual_try(): Let
the caller invoke innodb_update_cols().
innobase_rename_column_try(): Skip dropped columns.
commit_cache_norebuild(): Update table->fts->doc_col.
dict_mem_table_col_rename_low(): Skip dropped columns.
trx_undo_rec_get_partial_row(): Skip dropped columns.
trx_undo_update_rec_get_update(): Handle the metadata BLOB correctly.
trx_undo_page_report_modify(): Avoid out-of-bounds access to record fields.
Log metadata records consistently.
Apparently, the first fields of a clustered index may be updated
in an update_undo vector when the index is ID_IND of SYS_FOREIGN,
as part of renaming the table during ALTER TABLE. Normally, updates of
the PRIMARY KEY should be logged as delete-mark and an insert.
row_undo_mod_parse_undo_rec(), row_purge_parse_undo_rec():
Use trx_undo_metadata.
row_undo_mod_clust_low(): On metadata rollback, roll back the root page too.
row_undo_mod_clust(): Relax an assertion. The delete-mark flag was
repurposed for ALTER TABLE metadata records.
row_rec_to_index_entry_impl(): Add the template parameter mblob
and the optional parameter info_bits for specifying the desired new
info bits. For the metadata tuple, allow conversion between the original
format (ADD COLUMN only) and the generic format (with hidden BLOB).
Add the optional parameter "pad" to determine whether the tuple should
be padded to the index fields (on ALTER TABLE it should), or whether
it should remain at its original size (on rollback).
row_build_index_entry_low(): Clean up the code, removing
redundant variables and conditions. For instantly dropped columns,
generate a dummy value that is NULL, the empty string, or a
fixed length of NUL bytes, depending on the type of the dropped column.
row_upd_clust_rec_by_insert_inherit_func(): On the update of PRIMARY KEY
of a record that contained a dropped column whose value was stored
externally, we will be inserting a dummy NULL or empty string value
to the field of the dropped column. The externally stored column would
eventually be dropped when purge removes the delete-marked record for
the old PRIMARY KEY value.
btr_index_rec_validate(): Recognize the metadata record.
btr_discard_only_page_on_level(): Preserve the generic instant
ALTER TABLE metadata.
btr_set_instant(): Replaces page_set_instant(). This sets a clustered
index root page to the appropriate format, or upgrades from
the MDEV-11369 instant ADD COLUMN to generic ALTER TABLE format.
btr_cur_instant_init_low(): Read and validate the metadata BLOB page
before reconstructing the dictionary information based on it.
btr_cur_instant_init_metadata(): Do not read any lengths from the
metadata record header before reading the BLOB. At this point, we
would not actually know how many nullable fields the metadata record
contains.
btr_cur_instant_root_init(): Initialize n_core_null_bytes in one
of two possible ways.
btr_cur_trim(): Handle the mblob record.
row_metadata_to_tuple(): Convert a metadata record to a data tuple,
based on the new info_bits of the metadata record.
btr_cur_pessimistic_update(): Invoke row_metadata_to_tuple() if needed.
Invoke dtuple_convert_big_rec() for metadata records if the record is
too large, or if the mblob is not yet marked as externally stored.
btr_cur_optimistic_delete_func(), btr_cur_pessimistic_delete():
When the last user record is deleted, do not delete the
generic instant ALTER TABLE metadata record. Only delete
MDEV-11369 instant ADD COLUMN metadata records.
btr_cur_optimistic_insert(): Avoid unnecessary computation of rec_size.
btr_pcur_store_position(): Allow a logically empty page to contain
a metadata record for generic ALTER TABLE.
REC_INFO_DEFAULT_ROW_ADD: Renamed from REC_INFO_DEFAULT_ROW.
This is for the old instant ADD COLUMN (MDEV-11369) only.
REC_INFO_DEFAULT_ROW_ALTER: The more generic metadata record,
with additional information for dropped or reordered columns.
rec_info_bits_valid(): Remove. The only case when this would fail
is when the record is the generic ALTER TABLE metadata record.
rec_is_alter_metadata(): Check if a record is the metadata record
for instant ALTER TABLE (other than ADD COLUMN). NOTE: This function
must not be invoked on node pointer records, because the delete-mark
flag in those records may be set (it is garbage), and then a debug
assertion could fail because index->is_instant() does not necessarily
hold.
rec_is_add_metadata(): Check if a record is MDEV-11369 ADD COLUMN metadata
record (not more generic instant ALTER TABLE).
rec_get_converted_size_comp_prefix_low(): Assume that the metadata
field will be stored externally. In dtuple_convert_big_rec() during
the rec_get_converted_size() call, it would not be there yet.
rec_get_converted_size_comp(): Replace status,fields,n_fields with tuple.
rec_init_offsets_comp_ordinary(), rec_get_converted_size_comp_prefix_low(),
rec_convert_dtuple_to_rec_comp(): Add template<bool mblob = false>.
With mblob=true, process a record with a metadata BLOB.
rec_copy_prefix_to_buf(): Assert that no fields beyond the key and
system columns are being copied. Exclude the metadata BLOB field.
rec_convert_dtuple_to_metadata_comp(): Convert an alter metadata tuple
into a record.
row_upd_index_replace_metadata(): Apply an update vector to an
alter_metadata tuple.
row_log_allocate(): Replace dict_index_t::is_instant()
with a more appropriate condition that ignores dict_table_t::instant.
Only a table on which the MDEV-11369 ADD COLUMN was performed
can "lose its instantness" when it becomes empty. After
instant DROP COLUMN or reordering columns, we cannot simply
convert the table to the canonical format, because the data
dictionary cache and all possibly existing references to it
from other client connection threads would have to be adjusted.
row_quiesce_write_index_fields(): Do not crash when the table contains
an instantly dropped column.
Thanks to Thirunarayanan Balathandayuthapani for discussing the design
and implementing an initial prototype of this.
Thanks to Matthias Leich for testing.
row_log_table_get_pk_col(): Replace a condition that was inadvertently
removed in MDEV-16365. PRIMARY KEY columns are never allowed to be NULL,
and failure to enforce the constraint caused a null pointer to be
dereferenced in mem_heap_dup().
During a table-rebuilding online ALTER TABLE, if
dict_index_t::remove_instant() was invoked on the source table
(because it became empty), we would inadvertently change the way
how log records are written and parsed. We must keep the online_log
format unchanged throughout the whole table-rebuilding operation.
dict_col_t::def_t: Name the type of dict_col_t::def_val.
rec_get_n_add_field_len(), rec_set_n_add_field(): Define globally,
because these will be needed in row_log_table_low().
rec_init_offsets_temp(), rec_init_offsets_comp_ordinary(): Add
the parameter def_val for explicitly passing the default values
of the instantly added columns of the source table, so that
dict_index_t::instant_field_value() will not be called during
row_log_table_apply(). This allows us to consistently parse the
online_log records, even if the source table was converted
to the canonical non-instant format during the rebuild operation.
row_log_t::non_core_fields[]: The default values of the
instantly added columns on the source table; copied
during ha_innobase::prepare_inplace_alter_table()
while the table is exclusively locked.
row_log_t::instant_field_value(): Accessor to non_core_fields[],
analogous to dict_index_t::instant_field_value().
row_log_table_low(): Add fake_extra_size bytes to the record
header if the source table was converted to the canonical format
during the operation.
row_log_allocate(): Initialize row_log_t::non_core_fields.
