Fix an exception thrown while reading from ColumnFileTiny after add column

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #6726

Testing workload

1. Run TPCC workload
2. Add a column
3. Only read the newly added column

This might lead to an exception with error message Reading with fields but entry size is 0

Problem Summary:

Because only the newly added column is read, fields.length() == 0. It violates an assumption in BlobStore::read and an exception is thrown

tiflash/dbms/src/Storages/DeltaMerge/ColumnFile/ColumnFileTiny.cpp

Lines 62 to 80 in 4206a52

	PageStorage::PageReadFields fields;
	fields.first = data_page_id;
	for (size_t index = col_start; index < col_end; ++index)
	{
	const auto & cd = column_defines[index];
	if (auto it = colid_to_offset.find(cd.id); it != colid_to_offset.end())
	{
	auto col_index = it->second;
	fields.second.push_back(col_index);
	}
	else
	{
	// New column after ddl is not exist in this pack, fill with default value
	columns[index - col_start] = createColumnWithDefaultValue(cd, rows);
	}
	}
	auto page_map = page_reader.read({fields});
	Page page = page_map[data_page_id];

tiflash/dbms/src/Storages/Page/V3/BlobStore.cpp

Lines 582 to 586 in 4206a52

	// Read with `FieldReadInfos`, buf_size must not be 0.
	if (buf_size == 0)
	{
	throw Exception("Reading with fields but entry size is 0.", ErrorCodes::LOGICAL_ERROR);
	}

What is changed and how it works?

• In ColumnFileTiny::readFromDisk, skip reading from disk if all are filled by default column
• In BlobStore::read return an PageMap with empty Page instead of throwing exceptions
• Add some checks to ensure we will not save an empty block/empty column

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Fix the issue that reading the newly added column after an `ADD COLUMN` DDL might cause error

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Lloyd-Pottiger
• lidezhu

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[JaySon-Huang]

/cc @lidezhu @hongyunyan @flowbehappy

[JaySon-Huang]

/run-all-tests

[JaySon-Huang]

/run-unit-test

[Lloyd-Pottiger]

LGTM

[lidezhu]

LGTM

[JaySon-Huang]

/run-all-tests

[hongyunyan]

LGTM

[JaySon-Huang]

/merge

[ti-chi-bot]

@JaySon-Huang: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 734ebc0

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #6738.