TraceBuffer Class Reference

This class is used for storing unstructured optimizer trace text (as used by the Hypergraph optimizer). More...

#include <optimizer_trace.h>

Inheritance diagram for TraceBuffer:

Public Member Functions
	TraceBuffer (int64_t max_bytes)
int_type	overflow (int_type ch) override
	Called by std::ostream if the current segment is full. More...
template<typename Sink >
void	Consume (Sink sink)
	Apply 'sink' to each character in the trace text. More...
int64_t	excess_bytes () const
	Get the number of bytes that did not fit in m_segments. More...
std::string	ToString () const
	Return a copy of the contents as a string. More...

Static Public Attributes
static constexpr int64_t	kSegmentSize {4096}
	The size of each consecutive buffer. More...

Private Types
using	Segment = std::array< char, kSegmentSize >
	A consecutive buffer. More...

Private Attributes
int64_t	m_max_segments
	Max number of segments (as given by the optimizer_trace_max_mem_size system variable). More...
std::deque< Segment >	m_segments
	The sequence of segments. More...
std::unique_ptr< Segment >	m_excess_segment
	If we fill m_max_segments, allocate a single extra segment that is repeatedly overwritten with any additional data. More...
int64_t	m_full_excess_segments {0}
	The number of full segments that did not fit in m_segments. More...

Detailed Description

This class is used for storing unstructured optimizer trace text (as used by the Hypergraph optimizer).

It is used as the std::streambuf object of an associated std::ostream (which writes the formatted text into a TraceBuffer object). The text is stored in a non-consecutive sequence of segments, where each segment has a chunk of consecutive memory. That way, the buffer can grow without having to copy the text into ever bigger buffers of consecutive memory.

Member Typedef Documentation

Segment

using TraceBuffer::Segment = std::array<char, kSegmentSize>

private

A consecutive buffer.

Constructor & Destructor Documentation

TraceBuffer()

TraceBuffer::TraceBuffer ( int64_t  max_bytes )

inlineexplicit

Parameters

max_bytes

The maximal number of trace bytes, as given by the optimizer_trace_max_mem_size system variable.

Member Function Documentation

Consume()

template<typename Sink >

void TraceBuffer::Consume ( Sink  sink )

inline

Apply 'sink' to each character in the trace text.

Free each segment when its contents have been consumed. (That way, we avoid storing two copies of a potentially huge trace at the same time.)

excess_bytes()

int64_t TraceBuffer::excess_bytes ( ) const

inline

Get the number of bytes that did not fit in m_segments.

overflow()

std::streambuf::int_type TraceBuffer::overflow ( int_type  ch )

override

Called by std::ostream if the current segment is full.

Allocate a new segment (or use m_excess_segment if we have reached m_max_segments) and put 'ch' at the beginning of it.

ToString()

std::string TraceBuffer::ToString ( ) const

inline

Return a copy of the contents as a string.

This may be expensive for large traces, and is only intended for unit tests.

Member Data Documentation

kSegmentSize

constexpr int64_t TraceBuffer::kSegmentSize {4096}

staticconstexpr

The size of each consecutive buffer.

m_excess_segment

std::unique_ptr<Segment> TraceBuffer::m_excess_segment

private

If we fill m_max_segments, allocate a single extra segment that is repeatedly overwritten with any additional data.

This field will point to that segment.

m_full_excess_segments

int64_t TraceBuffer::m_full_excess_segments {0}

private

The number of full segments that did not fit in m_segments.

m_max_segments

int64_t TraceBuffer::m_max_segments

private

Max number of segments (as given by the optimizer_trace_max_mem_size system variable).

m_segments

std::deque<Segment> TraceBuffer::m_segments

private

The sequence of segments.

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The documentation for this class was generated from the following files:

• sql/join_optimizer/optimizer_trace.h
• sql/join_optimizer/optimizer_trace.cc