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https://github.com/jesperborgstrup/Py-IBLT
A Python implementation of Invertible Bloom Lookup Tables
https://github.com/jesperborgstrup/Py-IBLT
Last synced: 3 days ago
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A Python implementation of Invertible Bloom Lookup Tables
- Host: GitHub
- URL: https://github.com/jesperborgstrup/Py-IBLT
- Owner: jesperborgstrup
- License: mit
- Created: 2014-08-29T08:38:25.000Z (about 10 years ago)
- Default Branch: master
- Last Pushed: 2014-10-23T14:53:06.000Z (about 10 years ago)
- Last Synced: 2024-08-01T22:56:31.322Z (3 months ago)
- Language: Python
- Size: 154 KB
- Stars: 80
- Watchers: 4
- Forks: 7
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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- starred-awesome - Py-IBLT - A Python implementation of Invertible Bloom Lookup Tables (Python)
README
# Py-IBLT
A Python implementation of [Invertible Bloom Lookup Tables](http://arxiv.org/abs/1101.2245)
## Invertible Bloom Lookup Table
From the abstract of the paper (2011):
We present a version of the Bloom filter data structure that supports not only the insertion, deletion, and lookup of key-value pairs, but also allows a complete listing of its contents with high probability, as long the number of key-value pairs is below a designed threshold. Our structure allows the number of key-value pairs to greatly exceed this threshold during normal operation. Exceeding the threshold simply temporarily prevents content listing and reduces the probability of a successful lookup. If later entries are deleted to return the structure below the threshold, everything again functions appropriately. We also show that simple variations of our structure are robust to certain standard errors, such as the deletion of a key without a corresponding insertion or the insertion of two distinct values for a key. The properties of our structure make it suitable for several applications, including database and networking applications that we highlight.
## Notes
* Records that are deleted without a corresponding insert operation can be recovered with the `get` and `list_entries` functions.
* Error detection using `hashValueSum` as described in the paper is currently not implemented.
* Duplicate keys are not supported.
## Usage
### Constructor
Use the constructor to create a new IBLT:
```
from iblt import IBLT
t = IBLT( m, k, key_size, value_size, hash_key_sum_size=10, hash=None )
```
*m* is the amount of cells in underlying lookup table, and is closely related to the threshold value that determines how many key/value pairs the IBLT can hold before giving inconclusive answers to queries.
*k* is the amount of hash functions to be used.
*key_size* is maximum size for keys.
*value_size* is maximum size for values.
*hash_key_sum_size* is amount of bytes used for the hashkeySum field.
*hash* is function( i, value ), where i is index of hash function and value is value to be hashed (or None for default hash functions).
### Insert and delete
The `insert` function inserts a key/value pair into the IBLT.
```
t.insert( key, value )
```
The `delete` function likewise deletes a key/value pair from the IBLT.
```
t.delete( key, value )
```
The `insert` and `delete` functions do not have any return values.
### Retrieving a value based on a key
The `get` function tries to retrieve a value by key and gives you additional information on how the operation went:
```
t.get( key )
```
For the `get` function, the return value is `( , )`.
The `` value can be one of the following four possibilities:
* `IBLT.RESULT_GET_NO_MATCH` It is certain that no such key exists in the table. `` is `None`.
* `IBLT.RESULT_GET_MATCH` The key was previously inserted into the table and the value is returned in ``.
* `IBLT.RESULT_GET_DELETED_MATCH` The key was found, but it had been deleted instead of inserted and the value is returned in ``.
* `IBLT.RESULT_GET_INCONCLUSIVE` It wasn't possible to determine if the key was in the table or not. `` is `None`.
### Listing entries
The `list_entries` function tries to extract a complete list of all entries in the table. It either returns all entries or an incomplete list:
```
t.list_entries()
```
The return value of `list_entries` is `( , [], [] )`.
The `` value is one of two possibilities:
* `IBLT.RESULT_LIST_ENTRIES_COMPLETE` The entries lists are complete.
* `IBLT.RESULT_LIST_ENTRIES_INCOMPLETE`: It wasn't possible to extract a complete listing. Only the returned entries were recoverable.
The `` list contains all recoverable entries that have been inserted into the table.
Likewise, the `` list contains all recoverable entries that have been deleted from the table without being inserted.
### Serializing and unserializing
Table instances have a `serialize` function, that takes no argument and serializes the data and metadata of the table for into a bitstring storage or communication.
Likewise, the IBLT class has a static `unserialize` function that takes the serialized bitstring and constructs a copy of the table from the bitstring.
```
# t is an IBLT instance
s = t.serialize()
# Prints True
print IBLT.unserialize( s ) == t
```
#### Serialized data format:
```
[ Magic bytes ][ Header ][ Data ]
4 bytes 24 bytes
Magic bytes:
0x49 0x42 0x4C 0x54 (ASCII for IBLT)
Header:
[ Cell count (m) ]
32-bit uint
[ Key sum length ][ Value sum length ]
32-bit uint 32-bit uint
[ HashKeySum length ][ ValueKeySum length ]
32-bit uint 32-bit uint
[ # hash funcs (k) ]
32-bit uint
Data:
For each of the m cells:
[ Count ][ keySum ][ valueSum ][ hashKeySum ][ valueKeySum ]
32-bit int
```
## License
The MIT License (MIT)
Copyright (c) 2014 Jesper Borgstrup
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.