Optimizing Struct Field Alignment #876
Description
Overview
In file: db.go, the fields of the Options struct are organized in a way that takes more memory. The fields of the struct can be sorted in a way that takes less memory than the initial alignment.
// Options represents the options that can be set when opening a database.
type Options struct {
// Timeout is the amount of time to wait to obtain a file lock.
// When set to zero it will wait indefinitely.
Timeout time.Duration
// Sets the DB.NoGrowSync flag before memory mapping the file.
NoGrowSync bool
// Do not sync freelist to disk. This improves the database write performance
// under normal operation, but requires a full database re-sync during recovery.
NoFreelistSync bool
// PreLoadFreelist sets whether to load the free pages when opening
// the db file. Note when opening db in write mode, bbolt will always
// load the free pages.
PreLoadFreelist bool
// FreelistType sets the backend freelist type. There are two options. Array which is simple but endures
// dramatic performance degradation if database is large and fragmentation in freelist is common.
// The alternative one is using hashmap, it is faster in almost all circumstances
// but it doesn't guarantee that it offers the smallest page id available. In normal case it is safe.
// The default type is array
FreelistType FreelistType
// Open database in read-only mode. Uses flock(..., LOCK_SH |LOCK_NB) to
// grab a shared lock (UNIX).
ReadOnly bool
// Sets the DB.MmapFlags flag before memory mapping the file.
MmapFlags int
// InitialMmapSize is the initial mmap size of the database
// in bytes. Read transactions won't block write transaction
// if the InitialMmapSize is large enough to hold database mmap
// size. (See DB.Begin for more information)
//
// If <=0, the initial map size is 0.
// If initialMmapSize is smaller than the previous database size,
// it takes no effect.
InitialMmapSize int
// PageSize overrides the default OS page size.
PageSize int
// NoSync sets the initial value of DB.NoSync. Normally this can just be
// set directly on the DB itself when returned from Open(), but this option
// is useful in APIs which expose Options but not the underlying DB.
NoSync bool
// OpenFile is used to open files. It defaults to os.OpenFile. This option
// is useful for writing hermetic tests.
OpenFile func(string, int, os.FileMode) (*os.File, error)
// Mlock locks database file in memory when set to true.
// It prevents potential page faults, however
// used memory can't be reclaimed. (UNIX only)
Mlock bool
// Logger is the logger used for bbolt.
Logger Logger
}For the above alignment, the size of the struct is 104 bytes (for 64-bit systems). It can be reduced to 80 bytes by aligning the fields as follows:
type Options struct {
// Timeout is the amount of time to wait to obtain a file lock.
// When set to zero it will wait indefinitely.
Timeout time.Duration
// FreelistType sets the backend freelist type. There are two options. Array which is simple but endures
// dramatic performance degradation if database is large and fragmentation in freelist is common.
// The alternative one is using hashmap, it is faster in almost all circumstances
// but it doesn't guarantee that it offers the smallest page id available. In normal case it is safe.
// The default type is array
FreelistType FreelistType
// Sets the DB.MmapFlags flag before memory mapping the file.
MmapFlags int
// InitialMmapSize is the initial mmap size of the database
// in bytes. Read transactions won't block write transaction
// if the InitialMmapSize is large enough to hold database mmap
// size. (See DB.Begin for more information)
//
// If <=0, the initial map size is 0.
// If initialMmapSize is smaller than the previous database size,
// it takes no effect.
InitialMmapSize int
// PageSize overrides the default OS page size.
PageSize int
// OpenFile is used to open files. It defaults to os.OpenFile. This option
// is useful for writing hermetic tests.
OpenFile func(string, int, os.FileMode) (*os.File, error)
// Logger is the logger used for bbolt.
Logger Logger
// Mlock locks database file in memory when set to true.
// It prevents potential page faults, however
// used memory can't be reclaimed. (UNIX only)
Mlock bool
// Sets the DB.NoGrowSync flag before memory mapping the file.
NoGrowSync bool
// Do not sync freelist to disk. This improves the database write performance
// under normal operation, but requires a full database re-sync during recovery.
NoFreelistSync bool
// PreLoadFreelist sets whether to load the free pages when opening
// the db file. Note when opening db in write mode, bbolt will always
// load the free pages.
PreLoadFreelist bool
// Open database in read-only mode. Uses flock(..., LOCK_SH |LOCK_NB) to
// grab a shared lock (UNIX).
ReadOnly bool
// NoSync sets the initial value of DB.NoSync. Normally this can just be
// set directly on the DB itself when returned from Open(), but this option
// is useful in APIs which expose Options but not the underlying DB.
NoSync bool
}Sponsorship and Support:
This work is done by the security researchers from OpenRefactory and is supported by the Open Source Security Foundation (OpenSSF): Project Alpha-Omega. Alpha-Omega is a project partnering with open source software project maintainers to systematically find new, as-yet-undiscovered vulnerabilities in open source code - and get them fixed - to improve global software supply chain security.
The bug is found by running the iCR tool by OpenRefactory, Inc. and then manually triaging the results.