Other usage if persistent statistics is checking 'stats_is_read' in
caller, which is why this was not noticed earlier.
Other things:
- Simplified no_stat_values_provided
Example of what causes the problem:
T1: ANALYZE TABLE starts to collect statistics
T2: ALTER TABLE starts by deleting statistics for all changed fields,
then creates a temp table and copies data to it.
T1: ANALYZE ends and writes to the statistics tables.
T2: ALTER TABLE renames temp table in place of the old table.
Now the statistics from analyze matches the old deleted tables.
Fixed by waiting to delete old statistics until ALTER TABLE is
the only one using the old table and ensure that rename of columns
can handle swapping of column names.
rename_columns_in_stat_table() (former rename_column_in_stat_tables())
now takes a list of columns to rename. It uses the following algorithm
to update column_stats to be able to handle circular renames
- While there are columns to be renamed and it is the first loop or
last rename loop did change something.
- Loop over all columns to be renamed
- Change column name in column_stat
- If fail because of duplicate key
- If this is first change attempt for this column
- Change column name to a temporary column name
- If there was a conflicting row, replace it with the current row.
else
- Remove entry from column list
- Loop over all remaining columns in the list
- Remove the conflicting row
- Change column from temporary name to final name in column_stat
Other things:
- Don't flush tables for every operation. Only flush when all updates
are done.
- Rename of columns was not handled in case of ALGORITHM=copy (old bug).
- Fixed that we do not collect statistics for hidden hash columns
used by UNIQUE constraint on long values.
- Fixed that we do not collect statistics for blob columns referred by
generated virtual columns. This was achieved by storing the fields for
which we want to have statistics in table->has_value_set instead of
in table->read_set.
- Rename of indexes was not handled for persistent statistics.
- This is now handled similar as rename of columns. Renamed columns
are now stored in 'rename_stat_indexes' and handled in
Alter_info::delete_statistics() together with drooped indexes.
- ALTER TABLE .. ADD INDEX may instead of creating a new index rename
an existing generated foreign key index. This was not reflected in
the index_stats table because this was handled in
mysql_prepare_create_table instead instead of in the mysql_alter() code.
Fixed by adding a call in mysql_prepare_create_table() to drop the
changed index.
I also had to change the code that 'marked the index' to be ignored
with code that would not destroy the original index name.
Reviewer: Sergei Petrunia <sergey@mariadb.com>
This commits enables reloading of engine-independent statistics
without flushing the table from table definition cache.
This is achieved by allowing multiple version of the
TABLE_STATISTICS_CB object and having independent pointers to it in
TABLE and TABLE_SHARE. The TABLE_STATISTICS_CB object have reference
pointers and are freed when no one is pointing to it anymore.
TABLE's TABLE_STATISTICS_CB pointer is updated to use the
TABLE_SHARE's pointer when read_statistics_for_tables() is called at
the beginning of a query.
Main changes:
- read_statistics_for_table() will allocate an new TABLE_STATISTICS_CB
object.
- All get_stat_values() functions has a new parameter that tells
where collected data should be stored. get_stat_values() are not
using the table_field object anymore to store data.
- All get_stat_values() functions returns 1 if they found any
data in the statistics tables.
Other things:
- Fixed INSERT DELAYED to not read statistics tables.
- Removed Statistics_state from TABLE_STATISTICS_CB as this is not
needed anymore as wer are not changing TABLE_SHARE->stats_cb while
calculating or loading statistics.
- Store values used with store_from_statistical_minmax_field() in
TABLE_STATISTICS_CB::mem_root. This allowed me to remove the function
delete_stat_values_for_table_share().
- Field_blob::store_from_statistical_minmax_field() is implemented
but is not normally used as we do not yet support EIS statistics
for blobs. For example Field_blob::update_min() and
Field_blob::update_max() are not implemented.
Note that the function can be called if there is an concurrent
"ALTER TABLE MODIFY field BLOB" running because of a bug in
ALTER TABLE where it deletes entries from column_stats
before it has an exclusive lock on the table.
- Use result of field->val_str(&val) as a pointer to the result
instead of val (safetly fix).
- Allocate memory for collected statistics in THD::mem_root, not in
in TABLE::mem_root. This could cause the TABLE object to grow if a
ANALYZE TABLE was run many times on the same table.
This was done in allocate_statistics_for_table(),
create_min_max_statistical_fields_for_table() and
create_min_max_statistical_fields_for_table_share().
- Store in TABLE_STATISTICS_CB::stats_available which statistics was
found in the statistics tables.
- Removed index_table from class Index_prefix_calc as it was not used.
- Added TABLE_SHARE::LOCK_statistics to ensure we don't load EITS
in parallel. First thread will load it, others will reuse the
loaded data.
- Eliminate read_histograms_for_table(). The loading happens within
read_statistics_for_tables() if histograms are needed.
One downside is that if we have read statistics without histograms
before and someone requires histograms, we have to read all statistics
again (once) from the statistics tables.
A smaller downside is the need to call alloc_root() for each
individual histogram. Before we could allocate all the space for
histograms with a single alloc_root.
- Fixed bug in MyISAM and Aria where they did not properly notice
that table had changed after analyze table. This was not a problem
before this patch as then the MyISAM and Aria tables where flushed
as part of ANALYZE table which did hide this issue.
- Fixed a bug in ANALYZE table where table->records could be seen as 0
in collect_statistics_for_table(). The effect of this unlikely bug
was that a full table scan could be done even if
analyze_sample_percentage was not set to 1.
- Changed multiple mallocs in a row to use multi_alloc_root().
- Added a mutex protection in update_statistics_for_table() to ensure
that several tables are not updating the statistics at the same time.
Some of the changes in sql_statistics.cc are based on a patch from
Oleg Smirnov <olernov@gmail.com>
Co-authored-by: Oleg Smirnov <olernov@gmail.com>
Co-authored-by: Vicentiu Ciorbaru <cvicentiu@gmail.com>
Reviewer: Sergei Petrunia <sergey@mariadb.com>
This feature adds the functionality of ignorability for indexes.
Indexes are not ignored be default.
To control index ignorability explicitly for a new index,
use IGNORE or NOT IGNORE as part of the index definition for
CREATE TABLE, CREATE INDEX, or ALTER TABLE.
Primary keys (explicit or implicit) cannot be made ignorable.
The table INFORMATION_SCHEMA.STATISTICS get a new column named IGNORED that
would store whether an index needs to be ignored or not.
