Final added to:
- All reasonable classes inhereted from Field
- All classes inhereted from Protocol
- Almost all Handler classes
- Some important Item classes
The stripped size of mariadbd is just 4K smaller, but several object files
showed notable improvements in common execution paths.
- Checked field.o and item_sum.o
Other things:
- Added 'override' to a few class functions touched by this patch.
- Removed 'virtual' from a new class functions that had/got 'override'
- Changed Protocol_discard to inherit from Protocol instad of Protocol_text
The problem here is similar to the case with DISTINCT, the tree used for ORDER BY
needs to also hold the null bytes of the record. This was not done for GROUP_CONCAT
as NULLS are rejected by GROUP_CONCAT.
Also introduced a comparator function for the order by tree to handle null
values with JSON_ARRAYAGG.
For DISTINCT to be handled with JSON_ARRAYAGG, we need to make sure
that the Unique tree also holds the NULL bytes of a table record
inside the node of the tree. This behaviour for JSON_ARRAYAGG is
different from GROUP_CONCAT because in GROUP_CONCAT we just reject
NULL values for columns.
Also introduced a comparator function for the unique tree to handle null
values for distinct inside JSON_ARRAYAGG.
Backported from MYSQL
Bug #25331425: DISTINCT CLAUSE DOES NOT WORK IN GROUP_CONCAT
Issue:
------
The problem occurs when:
1) GROUP_CONCAT (DISTINCT ....) is used in the query.
2) Data size greater than value of system variable:
tmp_table_size.
The result would contain values that are non-unique.
Root cause:
-----------
An in-memory structure is used to filter out non-unique
values. When the data size exceeds tmp_table_size, the
overflow is written to disk as a separate file. The
expectation here is that when all such files are merged,
the full set of unique values can be obtained.
But the Item_func_group_concat::add function is in a bit of
hurry. Even as it is adding values to the tree, it wants to
decide if a value is unique and write it to the result
buffer. This works fine if the configured maximum size is
greater than the size of the data. But since tmp_table_size
is set to a low value, the size of the tree is smaller and
hence requires the creation of multiple copies on disk.
Item_func_group_concat currently has no mechanism to merge
all the copies on disk and then generate the result. This
results in duplicate values.
Solution:
---------
In case of the DISTINCT clause, don't write to the result
buffer immediately. Do the merge and only then put the
unique values in the result buffer. This has be done in
Item_func_group_concat::val_str.
Note regarding result file changes:
-----------------------------------
Earlier when a unique value was seen in
Item_func_group_concat::add, it was dumped to the output.
So result is in the order stored in SE. But with this fix,
we wait until all the data is read and the final set of
unique values are written to output buffer. So the data
appears in the sorted order.
This only fixes the cases when we have DISTINCT without ORDER BY clause
in GROUP_CONCAT.
Backported from MYSQL
Bug #25331425: DISTINCT CLAUSE DOES NOT WORK IN GROUP_CONCAT
Issue:
------
The problem occurs when:
1) GROUP_CONCAT (DISTINCT ....) is used in the query.
2) Data size greater than value of system variable:
tmp_table_size.
The result would contain values that are non-unique.
Root cause:
-----------
An in-memory structure is used to filter out non-unique
values. When the data size exceeds tmp_table_size, the
overflow is written to disk as a separate file. The
expectation here is that when all such files are merged,
the full set of unique values can be obtained.
But the Item_func_group_concat::add function is in a bit of
hurry. Even as it is adding values to the tree, it wants to
decide if a value is unique and write it to the result
buffer. This works fine if the configured maximum size is
greater than the size of the data. But since tmp_table_size
is set to a low value, the size of the tree is smaller and
hence requires the creation of multiple copies on disk.
Item_func_group_concat currently has no mechanism to merge
all the copies on disk and then generate the result. This
results in duplicate values.
Solution:
---------
In case of the DISTINCT clause, don't write to the result
buffer immediately. Do the merge and only then put the
unique values in the result buffer. This has be done in
Item_func_group_concat::val_str.
Note regarding result file changes:
-----------------------------------
Earlier when a unique value was seen in
Item_func_group_concat::add, it was dumped to the output.
So result is in the order stored in SE. But with this fix,
we wait until all the data is read and the final set of
unique values are written to output buffer. So the data
appears in the sorted order.
This only fixes the cases when we have DISTINCT without ORDER BY clause
in GROUP_CONCAT.
We have to include NULL in the result which the GOUP_CONCAT doesn't
always do. Also converting should be done into another String instance
as these can be same.
Item_sum_sp did not override val_native(). So the reported script
crashed in the default implementation in Item::val_native() on DBUG_ASSERT().
Implementing a correct Item_sum_sp::val_native().
e.g.
- dont -> don't
- occurence -> occurrence
- succesfully -> successfully
- easyly -> easily
Also remove trailing space in selected files.
These changes span:
- server core
- Connect and Innobase storage engine code
- OQgraph, Sphinx and TokuDB storage engines
Related to MDEV-21769.
The JSON_ARRAYAGG function extends the GROUP_CONCAT function and provides
a method of aggregating JSON results. The current implementation supports
DISTINCT and LIMIT but not ORDER BY (Oracle supports GROUP BY).
Adding GROUP BY support is possible but it requires some extra work as the
grouping appears to be done inside a temporary table that complicates
matters.
Added test cases that covert aggregation of all JSON types and JSON
validation for the generated results.
group concat tree is allocated in a memroot, so the only way to free
memory is to copy a part of the tree into a new memroot.
track the accumilated length of the result, and when it crosses
the threshold - copy the result into a new tree, free the old one.
Added support for usual agreggate UDF (UDAF)
Added remove() call support for more efficient window function processing
Added example of aggregate UDF with efficient windows function support
