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author | Monty <monty@mariadb.org> | 2020-09-16 11:23:50 +0300 |
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committer | Sergei Golubchik <serg@mariadb.org> | 2021-05-19 22:27:27 +0200 |
commit | 36cdd5c3cdb06d8538f64c0b312ffe4672a92e75 (patch) | |
tree | f1c675fab2e79fc8cd7466b080ddbc5ce3a1b920 /sql/sql_plugin.cc | |
parent | da85ad798708d045e7ba1963172daf81aeb80ab9 (diff) | |
download | mariadb-git-36cdd5c3cdb06d8538f64c0b312ffe4672a92e75.tar.gz |
Optimize usage of c_ptr(), c_ptr_quick() and String::alloc()
The problem was that when one used String::alloc() to allocate a string,
the String ensures that there is space for an extra NULL byte in the
buffer and if not, reallocates the string. This is a problem with the
String::set_int() that calls alloc(21), which forces extra
malloc/free calls to happen.
- We do not anymore re-allocate String if alloc() is called with the
Allocated_length. This reduces number of malloc() allocations,
especially one big re-allocation in Protocol::send_result_Set_metadata()
for almost every query that produced a result to the connnected client.
- Avoid extra mallocs when using LONGLONG_BUFFER_SIZE
This can now be done as alloc() doesn't increase buffers if new length is
not bigger than old one.
- c_ptr() is redesigned to be safer (but a bit longer) than before.
- Remove wrong usage of c_ptr_quick()
c_ptr_quick() was used in many cases to get the pointer to the used
buffer, even when it didn't need to be \0 terminated. In this case
ptr() is a better substitute.
Another problem with c_ptr_quick() is that it did not guarantee that
the string would be \0 terminated.
- item_val_str(), an API function not used currently by the server,
now always returns a null terminated string (before it didn't always
do that).
- Ensure that all String allocations uses STRING_PSI_MEMORY_KEY. The old
mixed usage of performance keys caused assert's when String buffers
where shrunk.
- Binary_string::shrink() is simplifed
- Fixed bug in String(const char *str, size_t len, CHARSET_INFO *cs) that
used Binary_string((char *) str, len) instead of Binary_string(str,len).
- Changed argument to String() creations and String.set() functions to use
'const char*' instead of 'char*'. This ensures that Alloced_length is
not set, which gives safety against someone trying to change the
original string. This also would allow us to use !Alloced_length in
c_ptr() if needed.
- Changed string_ptr_cmp() to use memcmp() instead of c_ptr() to avoid
a possible malloc during string comparision.
Diffstat (limited to 'sql/sql_plugin.cc')
-rw-r--r-- | sql/sql_plugin.cc | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/sql/sql_plugin.cc b/sql/sql_plugin.cc index 02ae08c910c..195267b9abc 100644 --- a/sql/sql_plugin.cc +++ b/sql/sql_plugin.cc @@ -404,12 +404,16 @@ static int item_value_type(struct st_mysql_value *value) static const char *item_val_str(struct st_mysql_value *value, char *buffer, int *length) { - String str(buffer, *length, system_charset_info), *res; + size_t org_length= *length; + String str(buffer, org_length, system_charset_info), *res; if (!(res= ((st_item_value_holder*)value)->item->val_str(&str))) return NULL; *length= res->length(); - if (res->c_ptr_quick() == buffer) + if (res->ptr() == buffer && res->length() < org_length) + { + buffer[res->length()]= 0; return buffer; + } /* Lets be nice and create a temporary string since the |