pmemkv

Key/Value Datastore for Persistent Memory

This is experimental pre-release software and should not be used in production systems. APIs and file formats may change at any time without preserving backwards compatibility. All known issues and limitations are logged as GitHub issues.

Overview

pmemkv is a local/embedded key-value datastore optimized for persistent memory. Rather than being tied to a single language or backing implementation, pmemkv provides different options for storage engines and language bindings.

• Installation
• Storage Engines
• Language Bindings
• Tools and Utilities

Installation

pmemkv does not currently provide install packages, but our installation guide provides detailed instructions, including configuring DAX and pool sets.

• Installing on Fedora
• Building from Sources

Storage Engines

pmemkv provides multiple storage engines with vastly different implementations. Since all engines conform to the same common API, any engine can be used with common pmemkv utilities and language bindings. Engines are requested at runtime by name. Contributing a new engine is easy and encouraged!

Available Engines

Engine	Description	Stable?	Thread-Safe?	Iterable?	Large Values?
blackhole	Accepts everything, returns nothing	Yes	Yes	No	Yes
kvtree3	Hybrid B+ persistent tree	Yes	No	Yes	Yes
vmap	Volatile hash map	No	No	Yes	Yes
vcmap	Volatile concurrent hash map	No	Yes	Yes	Yes
btree	Copy-on-write B+ persistent tree	No	No	Yes	No

Language Bindings

pmemkv is written in C and C++. Developers can either use native C++ classes directly, or use our extern "C" API, or use one of several high-level language bindings that are based on the extern "C" API.

C++ Example

#include <iostream>
#include "libpmemkv.h"

#define LOG(msg) std::cout << msg << "\n"

using namespace pmemkv;

int main() {
    LOG("Starting engine");
    KVEngine* kv = KVEngine::Start("kvtree3", "{\"path\":\"/dev/shm/pmemkv\"}");

    LOG("Putting new key");
    KVStatus s = kv->Put("key1", "value1");
    assert(s == OK && kv->Count() == 1);

    LOG("Reading key back");
    string value;
    s = kv->Get("key1", &value);
    assert(s == OK && value == "value1");

    LOG("Iterating existing keys");
    kv->Put("key2", "value2");
    kv->Put("key3", "value3");
    kv->All([](int kb, const char* k) {
        LOG("  visited: " << k);
    });

    LOG("Removing existing key");
    s = kv->Remove("key1");
    assert(s == OK && !kv->Exists("key1"));

    LOG("Stopping engine");
    delete kv;
    return 0;
}

C Example

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "libpmemkv.h"

#define LOG(msg) printf("%s\n", msg)
#define MAX_VAL_LEN 64

void StartFailureCallback(void* context, const char* engine, const char* config, const char* msg) {
    printf("ERROR: %s\n", msg);
    exit(-1);
}

void AllCallback(void* context, int kb, const char* k) {
    printf("   visited: %s\n", k);
}

int main() {
    LOG("Starting engine");
    KVEngine* kv = kvengine_start(NULL, "kvtree3", "{\"path\":\"/dev/shm/pmemkv\"}", &StartFailureCallback);

    LOG("Putting new key");
    char* key1 = "key1";
    char* value1 = "value1";
    KVStatus s = kvengine_put(kv, strlen(key1), key1, strlen(value1), value1);
    assert(s == OK && kvengine_count(kv) == 1);

    LOG("Reading key back");
    char val[MAX_VAL_LEN];
    s = kvengine_get_copy(kv, strlen(key1), key1, MAX_VAL_LEN, val);
    assert(s == OK && !strcmp(val, "value1"));

    LOG("Iterating existing keys");
    char* key2 = "key2";
    char* value2 = "value2";
    char* key3 = "key3";
    char* value3 = "value3";
    kvengine_put(kv, strlen(key2), key2, strlen(value2), value2);
    kvengine_put(kv, strlen(key3), key3, strlen(value3), value3);
    kvengine_all(kv, NULL, &AllCallback);

    LOG("Removing existing key");
    s = kvengine_remove(kv, strlen(key1), key1);
    assert(s == OK && kvengine_exists(kv, strlen(key1), key1) == NOT_FOUND);

    LOG("Stopping engine");
    kvengine_stop(kv);
    return 0;
}

Other Languages

These bindings are maintained in separate GitHub repos, but are still kept in sync with the main pmemkv distribution.

• Java - https://github.com/pmem/pmemkv-java
• Node.js - https://github.com/pmem/pmemkv-nodejs
• Ruby - https://github.com/pmem/pmemkv-ruby

Tools and Utilities

Benchmarks, examples and other helpful utilities are available here:

https://github.com/pmem/pmemkv-tools