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Make EXPLAIN better at displaying MRR/BKA:

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- "Using MRR" is no longer shown with range access.
- Instead, both range and BKA accesses will show one of the following:
  = "Rowid-ordered scan"
  = "Key-ordered scan"
  = "Key-ordered Rowid-ordered scan"
depending on whether DS-MRR implementation will do scan keys in order, rowids in order,
or both.
- The patch also introduces a way for other storage engines/MRR implementations to
  pass information to EXPLAIN output about the properties of employed MRR scans.
This commit is contained in:
Sergey Petrunya
2011-04-02 14:04:45 +04:00
parent 886d84d6d1
commit 997445bc8e
46 changed files with 624 additions and 467 deletions
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32
sql/sql_join_cache.cc
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@ -2491,8 +2491,36 @@ void JOIN_CACHE::print_explain_comment(String *str)
str->append(join_alg);
str->append(STRING_WITH_LEN(" join"));
str->append(STRING_WITH_LEN(")"));
}
}
static void add_mrr_explain_info(String *str, uint mrr_mode, handler *file)
{
char mrr_str_buf[128]={0};
int len;
len= file->multi_range_read_explain_info(mrr_mode, mrr_str_buf,
sizeof(mrr_str_buf));
if (len > 0)
{
str->append(STRING_WITH_LEN("; "));
str->append(mrr_str_buf, len);
}
}
void JOIN_CACHE_BKA::print_explain_comment(String *str)
{
JOIN_CACHE::print_explain_comment(str);
add_mrr_explain_info(str, mrr_mode, join_tab->table->file);
}
void JOIN_CACHE_BKAH::print_explain_comment(String *str)
{
JOIN_CACHE::print_explain_comment(str);
add_mrr_explain_info(str, mrr_mode, join_tab->table->file);
}
/*
Initialize a hashed join cache