Hi Sergei, thanks for your comments. Did you also review the first patch? revno: 4009 committer: Sergey Vojtovich branch nick: 10.0 timestamp: Fri 2014-02-14 16:25:41 +0400 message: MDEV-5674 - Performance: my_hash_sort_bin is called too often - reduced number of my_hash_sort_bin() calls from 4 to 2 per query. Let MDL subsystem use pre-calculated hash value for hash inserts and deletes. - reduced number of memory accesses done by my_hash_sort_bin() On Sat, Mar 01, 2014 at 07:46:58PM +0100, Sergei Golubchik wrote:

Hi, Sergey!

On Feb 20, Sergey Vojtovich wrote:

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At lp:maria/10.0

------------------------------------------------------------ revno: 4007 revision-id: svoj@mariadb.org-20140220072533-ko14y1714ouvd2f7 parent: svoj@mariadb.org-20140214122541-tenvcllk760deai8 committer: Sergey Vojtovich branch nick: 10.0 timestamp: Thu 2014-02-20 11:25:33 +0400 message: MDEV-5674 - Performance: my_hash_sort_bin is called too often

It's MDEV-5675, not MDEV-5674 Right.

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Reuse MDL hash value in table cache: - MDL namespace is excluded from hash value calculation, so that hash value can be used by table cache as is - hash value for MDL is calculated as resulting hash value + MDL namespace - extended hash implementation to accept user defined hash function

This looks ok. I have a couple of comments, but they are mostly a question of taste. Up to you, you can push as is too.

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=== modified file 'sql/mdl.cc' --- a/sql/mdl.cc 2014-02-14 12:25:41 +0000 +++ b/sql/mdl.cc 2014-02-20 07:25:33 +0000 @@ -760,13 +760,22 @@ void MDL_map::init() }

+my_hash_value_type mdl_hash_function(const CHARSET_INFO *cs, + const uchar *key, size_t length) +{ + return *((my_hash_value_type*) (key - offsetof(MDL_key, m_ptr) + + offsetof(MDL_key, m_hash_value))) + + key[0];

I'd prefer to avoid pointer and offset juggling. Because you use a custom hash function anyway, you can directly pass MDL_key as your "key", then here you can use ((MDL_key*)key)->hash_value()

I'd prefer to avoid it too. But there is hashcmp() function which is called when there are many records in a hash bucket. It does my_strnncoll() and MDL_key as it is now is not good for strnncoll. There is another option: store hash value in m_ptr, but I don't find it any better than offset juggling.

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+} + /** Initialize the partition in the container with all MDL locks. */

=== modified file 'sql/mdl.h' --- a/sql/mdl.h 2014-02-14 12:25:41 +0000 +++ b/sql/mdl.h 2014-02-20 07:25:33 +0000 @@ -397,7 +396,11 @@ class MDL_key { return & m_namespace_to_wait_state_name[(int)mdl_namespace()]; } - ulong hash_value() const + my_hash_value_type hash_value() const + { + return m_hash_value + m_ptr[0];

I'm not sure it's a good idea, + is not a very good hash function :) On the other hand, I don't see anything immediately wrong with it in this particular case. Ok, let it be.

Well, it's a poor hash function indeed and suggestions are very welcome. But what's wrong about the idea? :)

Anyway, could you please use mdl_namespace() instead of m_ptr[0] where possible?

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@@ -405,12 +408,14 @@ class MDL_key private: MDL_key(const MDL_key &); /* not implemented */ MDL_key &operator=(const MDL_key &); /* not implemented */ + friend my_hash_value_type mdl_hash_function(const CHARSET_INFO *, + const uchar *, size_t);

You probably wouldn't need this friend, if you'd change mdl_hash_function() to use MDL_key::hash_value()

Right. Thanks, Sergey