Reads and writes access group "hints" file. More...

#include <AccessGroupHintsFile.h>

Collaboration diagram for Hypertable::AccessGroupHintsFile:

Public Member Functions
	AccessGroupHintsFile (const String &table, const String &start_row, const String &end_row)
	Constructor. More...

void	change_start_row (const String &start_row)
	Changes the start row. More...

void	change_end_row (const String &end_row)
	Changes the end row. More...

std::vector< AccessGroup::Hints > &	get ()
	Returns reference to internal hints vector. More...

void	set (const std::vector< AccessGroup::Hints > &hints)
	Replaces contents of internal hints vector. More...

void	write (String location)
	Write hints file. More...

void	read ()
	Reads hints file. More...

bool	exists ()
	Checks if hints file exists. More...

Private Member Functions
void	parse_header (const char input, const char *ag_base)
	Parses header portion of hints file. More...

Private Attributes
String	m_table_id
	Table ID string More...

String	m_start_row
	Start row. More...

String	m_end_row
	End row. More...

String	m_range_dir
	Range subdirectory (md5 of end row) More...

std::vector< AccessGroup::Hints >	m_hints
	Vector of access group hints. More...

Detailed Description

Reads and writes access group "hints" file.

There are some state variables in each access group object that are required immediately after the object is constructed. These variables improve the performance of the system, but are expensive to compute because it requires scanning the METADATA table entry for the parent range, and opening and loading the block indexes for all CellStores that make up the access group. To allow this state to be reconstructed cheaply on restart, these state variables are persisted to a hints file in the filesystem that is read before the access group objects are constructed. There is one hints file for each range that contains an entry for each access group that makes up the range. For each range, the hints file has the following path:

/hypertable/tables/<table-id>/default/<md5-end-row>/hints

This file is in YAML format and contains a version number, start row, end row, and one mapping for each access group with the following format:

Version: 2
Start Row: <start-row>
End Row: <start-row>
Access Groups: {
  ag_name: {
    LatestStoredRevision: <revision>,
    DiskUsage: $bytes,
    Files: $file_list
  }
  ...
}

The fields in the mapping for each access group are described below.

LatestStoredRevision - This is the revision number of the latest (or newest) cell persisted in the access group's cell stores. When replaying the commit log after a restart, the access group can safely drop any cell whose revision number is less than or equal to this value.
DiskUsage - This is the amount of disk space taken up by the access group's cell stores. This information is used to determine whether or not a range needs to be split.
Files: - This is a semicolon separated list of cell store files that are part of the access group. This is information is not required by the access group immediately after construction, but is persisted here to assist in disaster recovery if the METADATA table becomes corrupt or Hyperspace is lost.

The reason that the hints for all of the access groups are persisted to a single hints file for each range is to improve restart performance. Upon restart, a single file is read to obtain the hints for all access groups, regardless of the number of access groups.

Definition at line 91 of file AccessGroupHintsFile.h.

Constructor & Destructor Documentation

AccessGroupHintsFile::AccessGroupHintsFile	(	const String &	table,
		const String &	start_row,
		const String &	end_row
	)

Constructor.

Parameters

table	Table ID string
start_row	Start row of range
end_row	End row of range

Definition at line 49 of file AccessGroupHintsFile.cc.

Member Function Documentation

void AccessGroupHintsFile::change_end_row ( const String & end_row )

Changes the end row.

This method is called after a range split to change the end row that is used to compute the path name to the hints file.

Parameters

end_row End row of range

Definition at line 62 of file AccessGroupHintsFile.cc.

void AccessGroupHintsFile::change_start_row ( const String & start_row )

Changes the start row.

This method is called after a range split to change the start row that is written to the hints file.

Parameters

start_row Start row of range

Definition at line 57 of file AccessGroupHintsFile.cc.

bool AccessGroupHintsFile::exists ( )

Checks if hints file exists.

Returns: true if file exists, false otherwise

Definition at line 215 of file AccessGroupHintsFile.cc.

std::vector<AccessGroup::Hints>& Hypertable::AccessGroupHintsFile::get ( )

inline

Returns reference to internal hints vector.

Returns: reference to internal hints vector

Definition at line 120 of file AccessGroupHintsFile.h.

void AccessGroupHintsFile::parse_header	(	const char *	input,
		const char **	ag_base
	)

private

Parses header portion of hints file.

Parameters

input	Pointer to beginning of hints file content
ag_base	Address of return pointer to Access Group section

Definition at line 253 of file AccessGroupHintsFile.cc.

void AccessGroupHintsFile::read ( )

Reads hints file.

Definition at line 128 of file AccessGroupHintsFile.cc.

void Hypertable::AccessGroupHintsFile::set ( const std::vector< AccessGroup::Hints > & hints )

inline

Replaces contents of internal hints vector.

Parameters

hints Reference to vector of hints

Definition at line 127 of file AccessGroupHintsFile.h.

void AccessGroupHintsFile::write ( String location )

Write hints file.

Parameters

location Proxy name of server who owns the range (empty if unknown)

Definition at line 78 of file AccessGroupHintsFile.cc.

Member Data Documentation

String Hypertable::AccessGroupHintsFile::m_end_row

private

End row.

Definition at line 159 of file AccessGroupHintsFile.h.

std::vector<AccessGroup::Hints> Hypertable::AccessGroupHintsFile::m_hints

private

Vector of access group hints.

Definition at line 165 of file AccessGroupHintsFile.h.

String Hypertable::AccessGroupHintsFile::m_range_dir

private

Range subdirectory (md5 of end row)

Definition at line 162 of file AccessGroupHintsFile.h.

String Hypertable::AccessGroupHintsFile::m_start_row

private

Start row.

Definition at line 156 of file AccessGroupHintsFile.h.

String Hypertable::AccessGroupHintsFile::m_table_id

private

Table ID string

Definition at line 153 of file AccessGroupHintsFile.h.

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

/home/doug/src/hypertable/src/cc/Hypertable/RangeServer/AccessGroupHintsFile.h
/home/doug/src/hypertable/src/cc/Hypertable/RangeServer/AccessGroupHintsFile.cc

Public Member Functions

Private Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation