Backend: pmem

The pmem (persistent memory) backend stores data in persistent memory devices, providing near-memory performance with persistence across provider restarts. It relies on the PMDK (Persistent Memory Development Kit) software, and was designed for persistent memory devices ((Intel Optane DCPMM, NVDIMM, etc.).

When to use

Use the pmem backend when:

You have persistent memory hardware (Intel Optane, etc.)
You need both high performance and persistence
Data must survive provider restarts
You want byte-addressable persistent storage
Low latency is critical

Characteristics

Persistent: Data survives provider restarts and system reboots

Fast: Near-DRAM performance (100s of nanoseconds latency)

Byte-addressable: No block-level I/O overhead

Limited capacity: Pmem devices are typically smaller than SSDs

Power-fail safe: Writes are durable after return

Configuration

In Bedrock configuration:

{
    "providers": [{
        "type": "warabi",
        "provider_id": 42,
        "config": {
            "target": {
                "type": "pmem",
                "config": {
                    "path": "/mnt/pmem/warabi.pmem",
                    "create_if_missing_with_size": 10737418240,
                    "override_if_exists": false
                }
            }
        }
    }]
}

Configuration options:

path: File where data will be stored
create_if_missing_with_size: If the target path does not exist, create is with the specified size (in bytes). This size should be at least 8MB (8388608).
override_if_exists: whether to overwrite an existing target and recreate it.

In C++ code:

#include <warabi/Provider.hpp>

auto config = R"(
{
    "target": {
        "type": "pmem",
        "config": {
            "path": "/mnt/pmem/warabi.pmem",
            "create_if_missing_with_size": 10737418240
        }
    }
}
)";

warabi::Provider provider(engine, 42, config);

Pool management

The pmem backend creates a persistent memory pool at the specified path:

$ ls -lh /mnt/pmem
-rw-r--r-- 1 user group 10G Dec 31 10:00 warabi.pmem

This pool file persists across provider restarts. When the provider starts again with the same configuration, it opens the existing pool and all regions are still available.