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Fix: avoid using regex match, possibly containing alternation, as a key condition. #54696

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merged 2 commits into from
Sep 18, 2023
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Fix: avoid using regex match, possibly containing alternation, as a key condition. #54696

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c2d4628
we can't process regex with alternation here - bypass
yakov-olkhovskiy Sep 15, 2023
f52e87f
fix
yakov-olkhovskiy Sep 15, 2023
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7 changes: 6 additions & 1 deletion src/Storages/MergeTree/KeyCondition.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -421,7 +421,12 @@ const KeyCondition::AtomMap KeyCondition::atom_map
if (value.getType() != Field::Types::String)
return false;

String prefix = extractFixedPrefixFromRegularExpression(value.get<const String &>());
const String & expression = value.get<const String &>();
// This optimization can't process alternation - this would require a comprehensive parsing of regular expression.
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I thought a bit

  • whether the check should rather be moved into extractFixedPrefixFromRegularExpression() but I think it is okay to not do so
  • whether extractFixedPrefixFromRegularExpression() could be replaced by the more sophisticated regex parsing in OptimizedRegularExpression::analyze(), but again no. ::analyze() searches the longest substring and that's not necessarily the prefix.

Therefore, we can merge the fix. Thanks.

if (expression.contains('|'))
return false;

String prefix = extractFixedPrefixFromRegularExpression(expression);
if (prefix.empty())
return false;

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1 change: 1 addition & 0 deletions tests/queries/0_stateless/02462_match_regexp_pk.sql
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Expand Up @@ -7,3 +7,4 @@ SELECT count() FROM mt_match_pk WHERE match(v, '^ab');
SELECT count() FROM mt_match_pk WHERE match(v, '^a.');
SELECT count() FROM mt_match_pk WHERE match(v, '^ab*');
SELECT count() FROM mt_match_pk WHERE match(v, '^ac?');
SELECT count() FROM mt_match_pk WHERE match(v, '^a$|^b'); -- {serverError INDEX_NOT_USED}