Struct Options

pub struct Options { /* private fields */ }

Options for configuring the value log.

Implementations

impl Options

pub fn with_read(self, read: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option for read access.

This option, when true, will indicate that the file should be read-able if opened.

Examples

use valog::options::Options;

let opts = Options::new().with_read(true);

pub fn with_write(self, write: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option for write access.

This option, when true, will indicate that the file should be write-able if opened.

If the file already exists, any write calls on it will overwrite its contents, without truncating it.

Examples

use valog::options::Options;

let opts = Options::new().with_write(true);

pub fn with_append(self, append: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option for the append mode.

This option, when true, means that writes will append to a file instead of overwriting previous contents. Note that setting .write(true).append(true) has the same effect as setting only .append(true).

For most filesystems, the operating system guarantees that all writes are atomic: no writes get mangled because another process writes at the same time.

One maybe obvious note when using append-mode: make sure that all data that belongs together is written to the file in one operation. This can be done by concatenating strings before passing them to write(), or using a buffered writer (with a buffer of adequate size), and calling flush() when the message is complete.

If a file is opened with both read and append access, beware that after opening, and after every write, the position for reading may be set at the end of the file. So, before writing, save the current position (using seek(SeekFrom::Current(opts))), and restore it before the next read.

Note

This function doesn’t create the file if it doesn’t exist. Use the Options::with_create method to do so.

Examples

use valog::options::Options;

let opts = Options::new().with_append(true);

pub fn with_truncate(self, truncate: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option for truncating a previous file.

If a file is successfully opened with this option set it will truncate the file to opts length if it already exists.

The file must be opened with write access for truncate to work.

Examples

use valog::options::Options;

let opts = Options::new().with_write(true).with_truncate(true);

pub fn with_create(self, val: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option to create a new file, or open it if it already exists. If the file does not exist, it is created and set the lenght of the file to the given size.

In order for the file to be created, Options::with_write or Options::with_append access must be used.

See also std::fs::write() for a simple function to create a file with some given data.

Examples

use valog::options::Options;

let opts = Options::new().with_write(true).with_create(true);

pub fn with_create_new(self, val: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Sets the option to create a new file and set the file length to the given value, failing if it already exists.

No file is allowed to exist at the target location, also no (dangling) symlink. In this way, if the call succeeds, the file returned is guaranteed to be new.

This option is useful because it is atomic. Otherwise between checking whether a file exists and creating a new one, the file may have been created by another process (a TOCTOU race condition / attack).

If .with_create_new(true) is set, .with_create() and .with_truncate() are ignored.

The file must be opened with write or append access in order to create a new file.

Examples

use valog::options::Options;

let file = Options::new()
  .with_write(true)
  .with_create_new(true);

pub fn with_offset(self, offset: u64) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Configures the memory map to start at byte offset from the beginning of the file.

This option has no effect on anonymous memory maps or vec backed Log.

By default, the offset is 0.

Example

use valog::options::Options;

let opts = Options::new().with_offset(30);

pub fn with_stack(self, stack: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Configures the anonymous memory map to be suitable for a process or thread stack.

This option corresponds to the MAP_STACK flag on Linux. It has no effect on Windows.

This option has no effect on file-backed memory maps and vec backed Log.

Example

use valog::options::Options;

let stack = Options::new().with_stack(true);

pub fn with_huge(self, page_bits: Option<u8>) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Configures the anonymous memory map to be allocated using huge pages.

This option corresponds to the MAP_HUGETLB flag on Linux. It has no effect on Windows.

The size of the requested page can be specified in page bits. If not provided, the system default is requested. The requested length should be a multiple of this, or the mapping will fail.

This option has no effect on file-backed memory maps and vec backed Log.

Example

use valog::options::Options;

let stack = Options::new().with_huge(Some(8));

pub fn with_populate(self, populate: bool) -> Self

Available on crate feature memmap and non-target_family="wasm" only.

Populate (prefault) page tables for a mapping.

For a file mapping, this causes read-ahead on the file. This will help to reduce blocking on page faults later.

This option corresponds to the MAP_POPULATE flag on Linux. It has no effect on Windows.

This option has no effect on vec backed Log.

Example

use valog::options::Options;

let opts = Options::new().with_populate(true);

impl Options

pub const fn read(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be opened with read access.

Examples

use valog::options::Options;

let opts = Options::new().with_read(true);
assert_eq!(opts.read(), true);

pub const fn write(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be opened with write access.

Examples

use valog::options::Options;

let opts = Options::new().with_write(true);
assert_eq!(opts.write(), true);

pub const fn append(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be opened with append access.

Examples

use valog::options::Options;

let opts = Options::new().with_append(true);
assert_eq!(opts.append(), true);

pub const fn truncate(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be opened with truncate access.

Examples

use valog::options::Options;

let opts = Options::new().with_truncate(true);
assert_eq!(opts.truncate(), true);

pub const fn create(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be created if it does not exist.

Examples

use valog::options::Options;

let opts = Options::new().with_create(true);
assert_eq!(opts.create(), true);

pub const fn create_new(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the file should be created if it does not exist and fail if it does.

Examples

use valog::options::Options;

let opts = Options::new().with_create_new(true);
assert_eq!(opts.create_new(), true);

pub const fn offset(&self) -> u64

Available on crate feature memmap and non-target_family="wasm" only.

Returns the offset of the memory map.

Examples

use valog::options::Options;

let opts = Options::new().with_offset(30);
assert_eq!(opts.offset(), 30);

pub const fn stack(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the memory map should be suitable for a process or thread stack.

Examples

use valog::options::Options;

let opts = Options::new().with_stack(true);
assert_eq!(opts.stack(), true);

pub const fn huge(&self) -> Option<u8>

Available on crate feature memmap and non-target_family="wasm" only.

Returns the page bits of the memory map.

Examples

use valog::options::Options;

let opts = Options::new().with_huge(Some(8));
assert_eq!(opts.huge(), Some(8));

pub const fn populate(&self) -> bool

Available on crate feature memmap and non-target_family="wasm" only.

Returns true if the memory map should populate (prefault) page tables for a mapping.

Examples

use valog::options::Options;

let opts = Options::new().with_populate(true);
assert_eq!(opts.populate(), true);

impl Options

pub const fn new() -> Self

Creates a new set of options with the default values.

pub const fn with_reserved(self, reserved: u32) -> Self

Set the reserved bytes of the Log.

The reserved is used to configure the start position of the Log. This is useful when you want to add some bytes before the Log, e.g. when using the memory map file backed Log, you can set the reserved to the size to 8 to store a 8 bytes checksum.

The default reserved is 0.

Example

use valog::options::Options;

let opts = Options::new().with_reserved(8);

pub const fn with_sync(self, sync: bool) -> Self

Set if flush the data to the disk when new value is inserted.

Default is true.

Example

use valog::options::Options;

let opts = Options::new().with_sync(false);

pub const fn with_validate_checksum(self, validate_checksum: bool) -> Self

Set if validate the checksum of the value when reading the value.

Default is true.

Example

use valog::options::Options;

let opts = Options::new().with_validate_checksum(false);

pub const fn with_lock_meta(self, lock_meta: bool) -> Self

Set if lock the meta of the Log in the memory to prevent OS from swapping out the first page of Log. When using memory map backed Log, the meta of the Log is in the first page, meta is frequently accessed, lock (mlock on the first page) the meta can reduce the page fault, but yes, this means that one Log will have one page are locked in memory, and will not be swapped out. So, this is a trade-off between performance and memory usage.

Default is true.

This configuration has no effect on windows and vec backed Log.

Example

use valog::options::Options;

let opts = Options::new().with_lock_meta(false);

pub const fn with_magic_version(self, magic_version: u16) -> Self

Set the magic version of the value log.

This is used by the application using value log to ensure that it doesn’t open the value log with incompatible data format.

The default value is 0.

Example

use valog::options::Options;

let opts = Options::new().with_magic_version(1);

pub const fn with_freelist(self, freelist: Freelist) -> Self

Set the Freelist kind of the value log.

The default value is Freelist::Optimistic.

Example

use valog::options::{Options, Freelist};

let opts = Options::new().with_freelist(Freelist::Optimistic);

pub const fn with_unify(self, unify: bool) -> Self

Set if use the unify memory layout of the value log.

File backed value log has different memory layout with other kind backed value log, set this value to true will unify the memory layout of the value log, which means all kinds of backed value log will have the same memory layout.

This value will be ignored if the value log is backed by a file backed memory map.

The default value is false.

Example

use valog::options::Options;

let opts = Options::default().with_unify(true);

pub const fn with_maximum_value_size(self, size: u32) -> Self

Sets the maximum size of the value.

Default is u32::MAX.

Example

use valog::options::Options;

let options = Options::new().with_maximum_value_size(1024);

pub const fn with_capacity(self, capacity: u32) -> Self

Sets the capacity of the underlying Log.

Example

use valog::options::Options;

let options = Options::new().with_capacity(1024);

pub const fn reserved(&self) -> u32

Get the reserved of the Log.

The reserved is used to configure the start position of the Log. This is useful when you want to add some bytes before the Log, e.g. when using the memory map file backed Log, you can set the reserved to the size to 8 to store a 8 bytes checksum.

The default reserved is 0.

Example

use valog::options::Options;

let opts = Options::new().with_reserved(8);

assert_eq!(opts.reserved(), 8);

pub const fn sync(&self) -> bool

Get if flush the data to the disk when new value is inserted.

Default is true.

Example

use valog::options::Options;

let opts = Options::new().with_sync(false);

assert_eq!(opts.sync(), false);

pub const fn validate_checksum(&self) -> bool

Get if validate the checksum of the value when reading the value.

Default is true.

Example

use valog::options::Options;

let opts = Options::new().with_validate_checksum(false);

assert_eq!(opts.validate_checksum(), false);

pub const fn lock_meta(&self) -> bool

Get if lock the meta of the Log in the memory to prevent OS from swapping out the first page of Log. When using memory map backed Log, the meta of the Log is in the first page, meta is frequently accessed, lock (mlock on the first page) the meta can reduce the page fault, but yes, this means that one Log will have one page are locked in memory, and will not be swapped out. So, this is a trade-off between performance and memory usage.

Example

use valog::options::Options;

let opts = Options::new().with_lock_meta(false);

assert_eq!(opts.lock_meta(), false);

pub const fn maximum_value_size(&self) -> u32

Returns the maximum size of the value.

Default is u32::MAX. The maximum size of the value is u32::MAX - header.

Example

use valog::options::Options;

let options = Options::new().with_maximum_value_size(1024);
assert_eq!(options.maximum_value_size(), 1024);

pub const fn capacity(&self) -> u32

Returns the configuration of underlying Log size.

Example

use valog::options::Options;

let options = Options::new().with_capacity(1024);

pub const fn unify(&self) -> bool

Get if use the unify memory layout of the value log.

File backed value log has different memory layout with other kind backed value log, set this value to true will unify the memory layout of the value log, which means all kinds of backed value log will have the same memory layout.

This value will be ignored if the value log is backed by a file backed memory map.

The default value is false.

Example

use valog::options::Options;

let opts = Options::new().with_unify(true);

assert_eq!(opts.unify(), true);

pub const fn magic_version(&self) -> u16

Get the magic version of the value log.

This is used by the application using value log to ensure that it doesn’t open the value log with incompatible data format.

The default value is 0.

Example

use valog::options::Options;

let opts = Options::new().with_magic_version(1);

assert_eq!(opts.magic_version(), 1);

pub const fn freelist(&self) -> Freelist

Get the Freelist kind of the value log.

The default value is Freelist::Optimistic.

Example

use valog::options::{Options, Freelist};

let opts = Options::new().with_freelist(Freelist::Optimistic);

assert_eq!(opts.freelist(), Freelist::Optimistic);

Trait Implementations

impl Clone for Options

fn clone(&self) -> Options

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Options

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Options

fn default() -> Options

Returns the “default value” for a type.

impl Hash for Options

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Options

fn eq(&self, other: &Options) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Options

impl Eq for Options

impl StructuralPartialEq for Options