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MDEV-17301 Change of COLLATE unnecessarily requires ALGORITHM=COPY

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Patch is about two cases:
1) On some collate changes it's possible to rebuild only secondary indexes
2) For non-indexed columns collate can be changed INSTANTly

Implemented mostly in Field_{string,varstring,blob}::is_equal().
Make this method return how exactly collationa differs.
This information is later used by fill_alter_inplace_info() to pass
correct info to engine.
This commit is contained in:
Eugene Kosov
2019-06-14 12:18:49 +03:00
parent 72d3676fe5
commit 854c219a7f
10 changed files with 379 additions and 82 deletions
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14
sql/sql_type.cc
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@ -8363,20 +8363,10 @@ Charset::encoding_allows_reinterpret_as(const CHARSET_INFO *cs) const
bool
Charset::encoding_and_order_allow_reinterpret_as(CHARSET_INFO *cs) const
Charset::eq_collation_specific_names(CHARSET_INFO *cs) const
{
/*
Test quickly if we have two exactly equal CHARSET_INFO pointers.
This also handles a special case with my_charset_bin:
it does not have a collation name specific part in CHARSET_INFO::name,
which is just "binary" (without a character set name prefix),
so the code with collation_specific_name() below won't work for it.
*/
if (m_charset == cs)
return true;
if (!encoding_allows_reinterpret_as(cs))
return false;
LEX_CSTRING name0= collation_specific_name();
LEX_CSTRING name1= Charset(cs).collation_specific_name();
/* Empty collations are not equal */
return name0.length && !cmp(&name0, &name1);
}