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README.md

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+# uhashring
+
+![version](https://img.shields.io/pypi/v/uhashring.svg)
+![ci](https://github.com/ultrabug/uhashring/actions/workflows/ci.yml/badge.svg)
+
+**uhashring** implements **consistent hashing** in pure Python.
+
+Consistent hashing is mostly used on distributed
+systems/caches/databases as this avoid the total reshuffling of your
+key-node mappings when adding or removing a node in your ring (called
+continuum on libketama). More information and details about this can be
+found in the *literature* section.
+
+This full featured implementation offers:
+
+-   a lot of **convenient methods** to use your consistent hash ring in
+    real world applications.
+-   simple **integration** with other libs such as memcache through
+    monkey patching.
+-   a full [ketama](https://github.com/RJ/ketama) compatibility if you
+    need to use it (see important mention below).
+-   all the missing functions in the libketama C python binding (which
+    is not even available on pypi) for ketama users.
+-   possibility to **use your own weight and hash functions** if you
+    don't care about the ketama compatibility.
+-   **instance-oriented usage** so you can use your consistent hash ring
+    object directly in your code (see advanced usage).
+-   native **pypy support**, since this is a pure python library.
+-   tests of implementation, key distribution and ketama compatibility.
+
+Per node weight is also supported and will affect the nodes distribution
+on the ring.
+
+## Python 2 EOL
+
+If you need Python 2 support, make sure to use **uhashring==1.2** as
+v1.2 is the last release that will support it.
+
+## IMPORTANT
+
+Since v1.0 **uhashring** default has changed to use a md5 hash function
+with 160 vnodes (points) per node in the ring.
+
+This change was motivated by the fact that the ketama hash function has
+more chances of collisions and thus requires a complete ring
+regeneration when the nodes topology change. This could lead to degraded
+performances on rapidly changing or unstable environments where nodes
+keep going down and up. The md5 implementation provides a linear
+performance when adding or removing a node from the ring!
+
+Reminder: when using **uhashring** with the ketama implementation and
+get 40 vnodes and 4 replicas = 160 points per node in the ring.
+
+## Usage
+
+### Basic usage
+
+**uhashring** is very simple and efficient to use:
+
+```python
+from uhashring import HashRing
+
+# create a consistent hash ring of 3 nodes of weight 1
+hr = HashRing(nodes=['node1', 'node2', 'node3'])
+
+# get the node name for the 'coconut' key
+target_node = hr.get_node('coconut')
+```
+
+### Ketama usage
+
+Simply set the **hash_fn** parameter to **ketama**:
+
+```python
+from uhashring import HashRing
+
+# create a consistent hash ring of 3 nodes of weight 1
+hr = HashRing(nodes=['node1', 'node2', 'node3'], hash_fn='ketama')
+
+# get the node name for the 'coconut' key
+target_node = hr.get_node('coconut')
+```
+
+### Advanced usage
+
+```python
+from uhashring import HashRing
+
+# Mapping of dict configs
+# Omitted config keys will get a default value, so
+# you only need to worry about the ones you need
+nodes = {
+    'node1': {
+            'hostname': 'node1.fqdn',
+            'instance': redis.StrictRedis(host='node1.fqdn'),
+            'port': 6379,
+            'vnodes': 40,
+            'weight': 1
+        },
+    'node2': {
+            'hostname': 'node2.fqdn',
+            'instance': redis.StrictRedis(host='node2.fqdn'),
+            'port': 6379,
+            'vnodes': 40
+        },
+    'node3': {
+            'hostname': 'node3.fqdn',
+            'instance': redis.StrictRedis(host='node3.fqdn'),
+            'port': 6379
+        }
+    }
+
+# create a new consistent hash ring with the nodes
+hr = HashRing(nodes)
+
+# set the 'coconut' key/value on the right host's redis instance
+hr['coconut'].set('coconut', 'my_value')
+
+# get the 'coconut' key from the right host's redis instance
+hr['coconut'].get('coconut')
+
+# delete the 'coconut' key on the right host's redis instance
+hr['coconut'].delete('coconut')
+
+# get the node config for the 'coconut' key
+conf = hr.get('coconut')
+```
+
+### Default node configuration
+
+**uhashring** offers advanced node configuration for real applications,
+this is the default you get for every added node:
+
+```python
+{
+    'hostname': nodename,
+    'instance': None,
+    'port': None,
+    'vnodes': 40,
+    'weight': 1
+}
+```
+
+### Adding / removing nodes
+
+You can add and remove nodes from your consistent hash ring at any time.
+
+```python
+from uhashring import HashRing
+
+# this is a 3 nodes consistent hash ring
+hr = HashRing(nodes=['node1', 'node2', 'node3'])
+
+# this becomes a 2 nodes consistent hash ring
+hr.remove_node('node2')
+
+# add back node2
+hr.add_node('node2')
+
+# add node4 with a weight of 10
+hr.add_node('node4', {'weight': 10})
+```
+
+### Customizable node weight calculation
+
+```python
+from uhashring import HashRing
+
+def weight_fn(**conf):
+    """Returns the last digit of the node name as its weight.
+
+    :param conf: node configuration in the ring, example:
+        {
+         'hostname': 'node3',
+         'instance': None,
+         'nodename': 'node3',
+         'port': None,
+         'vnodes': 40,
+         'weight': 1
+        }
+    """
+    return int(conf['nodename'][-1])
+
+# this is a 3 nodes consistent hash ring with user defined weight function
+hr = HashRing(nodes=['node1', 'node2', 'node3'], weight_fn=weight_fn)
+
+# distribution with custom weight assignment
+print(hr.distribution)
+
+# >>> Counter({'node3': 240, 'node2': 160, 'node1': 80})
+```
+
+### Customizable hash function
+
+```python
+from uhashring import HashRing
+
+# import your own hash function (must be a callable)
+# in this example, MurmurHash v3
+from mmh3 import hash as m3h
+
+# this is a 3 nodes consistent hash ring with user defined hash function
+hr = HashRing(nodes=['node1', 'node2', 'node3'], hash_fn=m3h)
+
+# now all lookup operations will use the m3h hash function
+print(hr.get_node('my key hashed by your function'))
+```
+
+### HashRing options
+
+-   **nodes**: nodes used to create the continuum (see doc for format).
+-   **hash_fn**: use this callable function to hash keys, can be set to
+    'ketama' to use the ketama compatible implementation.
+-   **vnodes**: default number of vnodes per node.
+-   **weight_fn**: user provided function to calculate the node's
+    weight, gets the node conf dict as kwargs.
+-   **replicas**: use this to change ketama ring replicas (default: 4)
+
+### Available methods
+
+-   **add_node(nodename, conf)**: add (or overwrite) the node in the
+    ring with the given config.
+-   **get(key)**: returns the node object dict matching the hashed key.
+-   **get_key(key)**: alias of the current hashi method, returns the
+    hash of the given key.
+-   **get_instances()**: returns a list of the instances of all the
+    configured nodes.
+-   **get_node(key)**: returns the node name of the node matching the
+    hashed key.
+-   **get_node_hostname(key)**: returns the hostname of the node
+    matching the hashed key.
+-   **get_node_instance(key)**: returns the instance of the node
+    matching the hashed key.
+-   **get_node_port(key)**: returns the port of the node matching the
+    hashed key.
+-   **get_node_pos(key)**: returns the index position of the node
+    matching the hashed key.
+-   **get_node_weight(key)**: returns the weight of the node matching
+    the hashed key.
+-   **get_nodes()**: returns a list of the names of all the configured
+    nodes.
+-   **get_points()**: returns a ketama compatible list of (position,
+    nodename) tuples.
+-   **get_server(key)**: returns a ketama compatible (position,
+    nodename) tuple.
+-   **hashi(key)**: returns the hash of the given key (on ketama mode,
+    this is the same as libketama).
+-   **iterate_nodes(key, distinct)**: hash_ring compatibility
+    implementation, same as range but returns tuples as a generator.
+-   **print_continuum()**: prints a ketama compatible continuum report.
+-   **range(key, size, unique)**: returns a (unique) list of max (size)
+    nodes' configuration available in the consistent hash ring.
+-   **regenerate**: regenerate the ring from the current nodes
+    configuration, useful only when using *weight_fn*.
+-   **remove_node(nodename)**: remove the given node from the ring
+
+### Available properties
+
+-   **conf**: dict of all the nodes and their configuration.
+-   **continuum**: same as ring.
+-   **distribution**: counter of the nodes distribution in the
+    consistent hash ring.
+-   **nodes**: same as conf.
+-   **ring**: hash key/node mapping of the consistent hash ring.
+-   **size**: size of the consistent hash ring.
+
+## Integration (monkey patching)
+
+You can benefit from a consistent hash ring using **uhashring** monkey
+patching on the following libraries:
+
+### python-memcached
+
+```python
+import memcache
+
+from uhashring import monkey
+monkey.patch_memcache()
+
+mc = memcache.Client(['node1:11211', 'node2:11211'])
+```
+
+## Installation
+
+### Pypi
+
+Using pip:
+
+```bash
+$ pip install uhashring
+```
+
+### Gentoo Linux
+
+Using emerge:
+
+```bash
+$ sudo emerge -a uhashring
+```
+
+## Benchmark
+
+Usage of the ketama compatible hash (default) has some performance
+impacts. Contributions are welcome as to ways of improving this !
+
+> There is a big performance gap in the hash calculation between the
+> ketama C binding and its pure python counterpart.
+>
+> Python 3 is doing way better than python 2 thanks to its native
+> bytes/int representation.
+>
+> ***Quick benchmark, for 1 million generated ketama compatible keys:***
+> -   python_ketama C binding: 0.8427069187164307 s
+> -   python 2: 5.462762832641602 s
+> -   python 3: 3.570068597793579 s
+> -   pypy: 1.6146340370178223 s
+>
+> When using python 2 and ketama compatibility is not important, you can
+> get a better hashing speed using the other provided hashing.
+>
+> hr = HashRing(nodes=[], compat=False)
+>
+> ***Quick benchmark, for 1 million generated hash keys:***
+> -   python 2: 3.7595579624176025 s
+> -   python 3: 3.268343687057495 s
+> -   pypy: 1.9193649291992188 s
+
+## Literature
+
+-   consistent hashing:
+    <https://en.wikipedia.org/wiki/Consistent_hashing>
+-   web caching paper:
+    <http://www8.org/w8-papers/2a-webserver/caching/paper2.html>
+-   research paper:
+    <http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.23.3738>
+-   distributed hash table:
+    <https://en.wikipedia.org/wiki/Distributed_hash_table>
+
+## License
+
+BSD