Do not resend metadata, if metadata does not change between prepare and
execute of prepared statement, or between executes.
Currently, metadata of *every* prepared statement will be checksummed,
and change is detected once checksum changes.
This is not from ideal, performance-wise. The code for
better/faster detection of unchanged metadata, is already in place, but
currently disabled due to PS bugs, such as MDEV-23913.
Passing a null pointer to a nonnull argument is not only undefined
behaviour, but it also grants the compiler the permission to optimize
away further checks whether the pointer is null. GCC -O2 at least
starting with version 8 may do that, potentially causing SIGSEGV.
Protocol_local fixed so it can be used now.
Some Protocol:: methods made virtual so they can adapt.
as well as net_ok and net_send_error functions.
execute_sql_string function is exported to the plugins.
To be changed with the mysql_use_result.
An alternative implementation (replacing the one based on repertoire).
This implementation makes Field send itself to Protocol_text using
data type specific Protocol methods rather than field->val_str()
followed by protocol_text->store_str().
As now Field sends itself in the same way to all protocol types
(e.g. Protocol_binary, Protocol_text, Protocol_local),
the method Field::send_binary() was renamed just to Field::send().
Note, this change introduces symmetry between Field and Item,
because Items also send themself using a single method Item::send(),
which is used for *all* protocol types.
Performance improvement is achieved by the fact that Protocol_text
implements these data type specific methods using store_numeric_string_aux()
rather than store_string_aux(). The conversion now happens only when
character_set_results is not ASCII compatible character sets
(e.g. UCS2, UTF16, UTF32).
In the old code (before any MDEV-23162 work, e.g. as of 10.5.4),
Protocol_text::store(Field*) used val_str() for all data types.
So the execution went through the character set conversion routines
even for numeric and temporal data types.
Benchmarking summary (see details in MDEV-23478):
The new approach stably demonstrates additional improvement comparing
to the previous implementation (the smaller time - the better):
Original - the commit before MDEV-23162
be98036f25
1m9.336s
1m9.290s
1m9.300s
MDEV-23162 - the repertoire optimization
1m6.101s
1m5.988s
1m6.264s
MDEV-23478 - this commit
1m2.150s
1m2.079s
1m2.099s
- Better to use 'String *' directly.
- Added String::get_value(LEX_STRING*) for the few cases where we want to
convert a String to LEX_CSTRING.
Other things:
- Use StringBuffer for some functions to avoid mallocs
Avoid character set conversion for numeric data in this scenario:
SET NAMES utf8;
CREATE OR REPLACE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1);
SELECT a FROM t1;
- Renaming this virtual method store() to store_str():
store(const char *str, size_t length, CHARSET_INFO *src_cs, CHARSET_INFO *dst_cs)
We'll be adding more variants of store*() soon. This change will help to avoid
ambiguities during overloading.
- Adding a helper method store_ident().
- Renaming store_str(const LEX_CSTRING &s...) to store_lex_cstring(),
to avoid ambiguties during overloading.
- Adding a helper method store() for backward compatibility, to avoid a lot of
changes in the code now. But eventually we should replace store() to
non-ambiguius methods store_str() or store_ident().
- Adding a helper method Protocol::needs_conversion() and reusing it
in two places.
The COM_MULTI did not take off. No connector is using it.
Remove related code from server, and client.
If anything it is a step simplification of already-bloated
dispatch_command(), and related code.
When my_vsnprintf() is patched, the code protected disabled with
'WAITING_FOR_BUGFIX_TO_VSPRINTF' should be enabled again. Also all %b
formats in this patch should be revert to %s again
The problem happened because Item_ident_for_show did not implement val_native().
Solution:
- Removing class Item_ident_for_show
- Implementing a new method Protocol::send_list_fields() instead,
which accepts a List<Field> instead of List<Item> as input.
Now no any Item creation is done during mysqld_list_fields().
Adding helper methods, to reuse the code easier:
- Moved a part of Protocol::send_result_set_metadata(),
responsible for sending an individual field metadata,
into a new method Protocol_text::store_field_metadata().
Reusing it in both send_list_fields() and send_result_set_metadata().
- Adding Protocol_text::store_field_metadata()
- Adding Protocol_text::store_field_metadata_for_list_fields()
Note, this patch also automatically fixed another bug:
MDEV-18685 mysql_list_fields() returns DEFAULT 0 instead of DEFAULT NULL for view columns
The reason for this bug was that Item_ident_for_show::val_xxx() and get_date()
did not check field->is_null() before calling field->val_xxx()/get_date().
Now the default value is correctly sent by Protocol_text::store(Field*).
truncate incorrect values in convert_period_to_month() so that
PERIOD_DIFF never returns a value outside of 2^23 range.
And, for safety, increase buffer sizes for int10_to_str
to be sufficienly big for any int10_to_str result.
Renaming methods:
- Field::make_field(Send_field*) to make_send_field(..)
- Item::make_field(THD *,Send_field *) to make_send_field(..)
- Item::init_make_field(Send_field *, enum_field_type) to init_make_send_field(..)
These names looked similar to other functions that are used
for a very different purpose (creating Field instances):
- Public function "Field * make_field(..)"
- Method "Field *Column_defitinion::make_field(..)"
The rename makes it's easier to search the code using "grep".
