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dbms: made code more readable [#METR-19266]

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This commit is contained in:
Alexey Arno 2016-08-24 13:27:19 +03:00
parent cd0541134a
commit 824341c1c2
1 changed files with 61 additions and 50 deletions
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67
dbms/src/Storages/StorageLog.cpp
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@ -885,11 +885,36 @@ BlockInputStreams StorageLog::read(
0, std::numeric_limits<size_t>::max(),
settings.max_read_buffer_size));
}
else if (has_nullable_columns)
else
{
const Marks & marks = getMarksWithRealRowCount();
size_t marks_size = marks.size();
/// Given a thread, return the start of the area from which
/// it can read data, i.e. a mark number.
auto mark_from_thread = [&](size_t thread)
{
/// The computation below reflects the fact that marks
/// are uniformly distributed among threads.
return from_mark + thread * (to_mark - from_mark) / threads;
};
/// Given a thread, get the parameters that specify the area
/// from which it can read data, i.e. a mark number and a
/// maximum number of rows.
auto get_reader_parameters = [&](size_t thread)
{
size_t mark_number = mark_from_thread(thread);
size_t cur_total_row_count = ((thread == 0 && from_mark == 0)
? 0
: marks[mark_number - 1].rows);
size_t next_total_row_count = marks[mark_from_thread(thread + 1) - 1].rows;
size_t rows_limit = next_total_row_count - cur_total_row_count;
return std::make_pair(mark_number, rows_limit);
};
if (to_mark == std::numeric_limits<size_t>::max())
to_mark = marks_size;
@ -899,19 +924,15 @@ BlockInputStreams StorageLog::read(
if (threads > to_mark - from_mark)
threads = to_mark - from_mark;
if (has_nullable_columns)
{
for (size_t thread = 0; thread < threads; ++thread)
{
size_t mark_number = from_mark + thread * (to_mark - from_mark) / threads;
size_t mark_number;
size_t rows_limit;
std::tie(mark_number, rows_limit) = get_reader_parameters(thread);
size_t cur_total_row_count = ((thread == 0 && from_mark == 0)
? 0
: marks[from_mark + thread * (to_mark - from_mark) / threads - 1].rows);
size_t next_total_row_count = marks[from_mark + (thread + 1) * (to_mark - from_mark) / threads - 1].rows;
size_t rows_limit = next_total_row_count - cur_total_row_count;
/// We must have the same number of marks and of null marks.
/// This works since we have the same number of marks and null marks.
size_t null_mark_number = from_null_mark + (mark_number - from_mark);
res.push_back(std::make_shared<LogBlockInputStream>(
@ -926,32 +947,22 @@ BlockInputStreams StorageLog::read(
}
else
{
const Marks & marks = getMarksWithRealRowCount();
size_t marks_size = marks.size();
if (to_mark == std::numeric_limits<size_t>::max())
to_mark = marks_size;
if (to_mark > marks_size || to_mark < from_mark)
throw Exception("Marks out of range in StorageLog::read", ErrorCodes::LOGICAL_ERROR);
if (threads > to_mark - from_mark)
threads = to_mark - from_mark;
for (size_t thread = 0; thread < threads; ++thread)
{
size_t mark_number;
size_t rows_limit;
std::tie(mark_number, rows_limit) = get_reader_parameters(thread);
res.push_back(std::make_shared<LogBlockInputStream>(
max_block_size,
column_names,
*this,
from_mark + thread * (to_mark - from_mark) / threads,
marks[from_mark + (thread + 1) * (to_mark - from_mark) / threads - 1].rows -
((thread == 0 && from_mark == 0)
? 0
: marks[from_mark + thread * (to_mark - from_mark) / threads - 1].rows),
mark_number,
rows_limit,
settings.max_read_buffer_size));
}
}
}
return res;
}