ream - v0.1.0

ream/storage/kv/value

Store the information of the values for kv.

The events stored in the file are in the following format:

The KV system is split into two parts: the key store and the value store. The file is related to the value store. As we said it’s a file with the content marking the size of the value, if it’s deleted and the value itself.

The file is append only. When a value is written, it’s appended to the end of the file. When a value is deleted, it’s not deleted from the file, it’s marked as deleted. When a value is updated, it’s deleted and a new value is appended to the end of the file.

Types

Reason

</> 
pub type Reason {
  CapacityExceeded
}

Constructors 

  • CapacityExceeded

Value

</>

The information for a value. The fields are:

  • offset: the offset of the value in the file.
  • deleted: if the value is deleted.
  • data: the value. It can be None if we didn’t read the value yet.
  • file_id: the id of the file where the value is stored.
pub type Value {
  Value(
    offset: Int,
    deleted: Bool,
    data: Option(BitString),
    file_id: Int,
  )
}

Constructors 

  • Value(
  offset: Int,
  deleted: Bool,
  data: Option(BitString),
  file_id: Int,
)

ValueFile

</>

The information for the kv file. The fields are:

  • id: the id of the file. It’s intended to be a UUID but it’s stored as an Int.
  • handler: the file handler to read and write values.
  • size: the size of the file.
  • max_size: the maximum size of the file.
  • file_path: the path of the file.
pub type ValueFile {
  ValueFile(
    id: Int,
    handler: Pid,
    size: Int,
    max_size: Int,
    file_path: String,
  )
}

Constructors 

  • ValueFile(
  id: Int,
  handler: Pid,
  size: Int,
  max_size: Int,
  file_path: String,
)

ValueFileInfo

</>

The information for the kv file. The fields are:

  • file_id: the id of the file. It’s intended to be a UUID but it’s stored as an Int.
  • size: the size of the file.
  • entries: the number of entries in the file.
  • deleted: the number of deleted entries in the file.
pub type ValueFileInfo {
  ValueFileInfo(
    file_id: Int,
    size: Int,
    max_size: Int,
    entries: Int,
    deleted: Int,
  )
}

Constructors 

  • ValueFileInfo(
  file_id: Int,
  size: Int,
  max_size: Int,
  entries: Int,
  deleted: Int,
)

Constants

value_size_bits

</> 
pub const value_size_bits: Int = 32

Functions

close

</> 
pub fn close(vfile: ValueFile) -> Result(Nil, Reason)

Close a kv file. It closes the file handler.

create

</> 
pub fn create(base_path: String, max_size: Int) -> Result(
  ValueFile,
  Reason,
)

Create a new kv file. It creates a new file with a random UUID as the path for finding the file.

For example, if the UUID is f81d4fae-7dec-11d0-a765-00a0c91e6bf6, the file will be created in the following path: base_path/f81d4fae/7dec/11d0/a765/00a0c91e6bf6.

delete

</> 
pub fn delete(vfile: ValueFile, value: Value) -> Result(
  ValueFile,
  Reason,
)

Delete a value from the kv file. It marks the value as deleted. It returns the updated kv file with the new size.

get_file_info

</> 
pub fn get_file_info(vfile: ValueFile) -> ValueFileInfo

open

</> 
pub fn open(path: String, file_id: Int, max_size: Int) -> Result(
  ValueFile,
  Reason,
)

Open a kv file. It opens the file with the given file id. If the file doesn’t exist, it is creating it. The main difference with create is that open doesn’t generate a new UUID. It returns the kv file with the file handler and the file size.

read

</> 
pub fn read(vfile: ValueFile, offset: Int) -> Result(
  Value,
  Reason,
)

Read a value from the kv file. It reads the value and returns it as a BitString with the following format:

  • 4 bytes: the size of the value
  • 1 byte: 0 if the value is not deleted, 1 if it is
  • n bytes: the value

write

</> 
pub fn write(vfile: ValueFile, value: BitString) -> Result(
  #(ValueFile, Value),
  Reason,
)

write_value

</> 
pub fn write_value(vfile: ValueFile, value: Value) -> Result(
  ValueFile,
  Reason,
)

Write a value to the kv file. It writes the value in the following format:

  • 4 bytes: the size of the value
  • 1 byte: 0 if the value is not deleted, 1 if it is
  • n bytes: the value It returns the updated kv file with the new size.
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