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A joint patch for MDEV-19284 and MDEV-19285 (INSTANT ALTER)
This patch fixes: - MDEV-19284 INSTANT ALTER with ucs2-to-utf16 conversion produces bad data - MDEV-19285 INSTANT ALTER from ascii_general_ci to latin1_general_ci produces corrupt data These regressions were introduced in 10.4.3 by: - MDEV-15564 Avoid table rebuild in ALTER TABLE on collation or charset changes Changes: 1. Cleanup: Adding a helper method Field_longstr::csinfo_change_allows_instant_alter(), to remove some duplicate code in field.cc. 2. Cleanup: removing Type_handler::Charsets_are_compatible() and static function charsets_are_compatible() and introducing new methods in the recently added class Charset instead: - encoding_allows_reinterpret_as() - encoding_and_order_allow_reinterpret_as() 3. Bug fix: Removing the code that allowed instant conversion for ascii-to->8bit and ucs2-to->utf16. This actually fixes MDEV-19284 and MDEV-19285. 4. Bug fix: Adding a helper method Charset::collation_specific_name(). The old corresponding code in Type_handler::Charsets_are_compatible() was not safe against (badly named) user-defined collations whose character set name can be longer than collation name.
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@ -159,6 +159,14 @@ public:
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{
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swap_variables(CHARSET_INFO*, m_charset, other.m_charset);
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}
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/*
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Collation name without the character set name.
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For example, in case of "latin1_swedish_ci",
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this method returns "_swedish_ci".
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*/
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LEX_CSTRING collation_specific_name() const;
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bool encoding_allows_reinterpret_as(CHARSET_INFO *cs) const;
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bool encoding_and_order_allow_reinterpret_as(CHARSET_INFO *cs) const;
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};
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