README
¶
bfile
A buffer pool file I/O library for Go.
The purpose of the library is to provide I/O mechanisms for copying data to and from a buffer in user space and maintain complete control over how and when it transfers pages.
This is an alternative to using mmap on large DBMS like files.
Install
go get github.com/tidwall/bfile
Usage
Use the NewPager function to create a new Pager, which includes three
functions: ReadAt, WriteAt, and Flush.
The Pager reading and writing works like an os.File, but with an
automatically maintained pool of buffered pages.
// Open a file for read/write
f, err := os.OpenFile("bigfile.dat", os.O_RDWR, 0)
// Create a new Pager for accessing the data in opened file.
p := bfile.NewPager(f)
// Read some data at a specific offset.
data := make([]byte, 50)
n, err := p.ReadAt(data, 827364)
// Write some data at the same offset.
n, err := p.WriteAt([]byte("hello"), c)
// Flush unwritten data to the underlying os.File
err = p.Flush()
There's also a Stream object for sequentially reading and writing data, which
includes the three functions: Read, Write, and Flush.
// Create a new Pager
p := bfile.NewPager(f)
// Create a Stream that is backed by the Pager starting at a specific offset
s := p.Stream(827364)
// Read 50 bytes data at the offset 827364.
data := make([]byte, 50)
n, err := s.Read(data)
// Write the string "hello" at 827414, which is after the previous read.
n, err := s.Write([]byte("hello"))
// Flush unwritten data to the underlying os.File
err = p.Flush()
The default page size is 4096 and the default size of all buffered pages will
not exceed 8 MB.
These defaults can be changed by using the NewPagerSize function.
All operations are thread-safe.
Contact
Josh Baker @tidwall
License
Source code is available under the MIT License.
Documentation
¶
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type Pager ¶
type Pager struct {
// contains filtered or unexported fields
}
Pager is a page buffer that is backed by an os.File
func NewPagerSize ¶
NewPagerSize returns a new Pager with a custom page size and buffer size. The bufferSize is the maximum amount of memory dedicated to individual pages. Setting pageSize and bufferSize to zero will use their defaults, which are 4096 and 8 MB respectively. Custom values are rounded up to the nearest power of 2.
func (*Pager) ReadAt ¶
The byte offset off and len(b) must fall within the range of the size of the underlying file from Open or Create, otherwise an error is returned. ReadAt reads len(b) bytes from the File starting at byte offset off. It returns the number of bytes read and the error, if any. ReadAt returns a non-nil error when n < len(b).
Source Files