Configure the primary index

The primary index of an Aerospike namespace can be stored in three different mediums: shared memory (SHMem) by default, Intel® Optane™ Persistent Memory (PMem), or Flash device (on NVMe SSDs). Separate namespaces within the same cluster can use different types of primary index storage.

Note

Primary index storage (index-type) is not configurable in Aerospike Database Community Edition (CE). Its primary index storage is always volatile process memory, and the cluster node is not able to perform a fast restart.

To specify a primary index storage method, use the namespace configuration parameter index-type.

• The default index-type shmem stores primary index metadata in shared memory segments.
• index-type pmem specifies PMem storage for the namespace primary index.
• index-type flash specifies NVMe SSD storage for the namespace primary index.

For sizing information, see capacity planning.

Caution

On a systemd Linux OS you might need to increase TimeoutSec from the default of 15s. This setting is in /usr/lib/systemd/system/aerospike.service. This prevents systemd from killing the asd process prematurely while the service is being shutdown. The primary index clean-up process during shutdown might take longer than the default 15s. In Aerospike, this default value has been increased to 10 minutes as of server version 4.6.0.2.

Primary index in memory

By default the namespace primary index storage type in Aerospike Database Enterprise Edition variants (EE, FE, SE) is shared memory, equivalent to explicitly setting index-type shmem.

Primary index on Flash

The Aerospike All Flash feature allows primary indexes to be stored on an NVMe SSDs. This index storage method is typically used for extremely large primary indexes with relatively small records.

It is important to understand the subtleties of primary index on flash sizing as scaling up an All Flash namespace may require an increase of partition-tree-sprigs which would require a rolling cold restart.

Set kernel parameters

The following Linux kernel parameters are required in an index on Flash deployment. enforce-best-practices verifies that these kernel parameters have the expected values.

/proc/sys/vm/dirty_bytes = 16777216
/proc/sys/vm/dirty_background_bytes = 1
/proc/sys/vm/dirty_expire_centisecs = 1
/proc/sys/vm/dirty_writeback_centisecs = 10

• When running as non-root, you must prepare these values before running the Aerospike server.
• When running as root, the server configures them automatically.

Either way, if these parameters can’t be correctly set manually, or automatically by the server, the node will not be able to start up with a index-type flash configuration.

Caution

While it is advisable to adjust the kernel’s min_free_kbytes parameter in any configuration, it is especially important to do so when storing the primary index on Flash memory (All Flash). The Linux kernel will attempt to use all free space by caching disk writes. With All Flash configuration, this may result in an out of memory (OOM) kill if there isn’t enough free memory left for normal system operations. For this reason, Aerospike recommends setting min_free_kbytes=1153434 (1.1GB). For more information, see Best practices for Aerospike and Linux.

Prepare and mount Flash devices

Aerospike instantiates at least 4 different arena allocations (as files) for each device partition configured for use by the namespace. This helps reduce contention against the same arena, which improves performance during heavy insertion loads.

An XFS filesystem is recommended because it has been shown to provide better concurrent access to files than EXT4.

sudo mkfs.xfs -f /dev/nvme0
sudo mount /dev/nvme0 /mnt/nvme0

• Using more physical devices will improve performance through increased parallelism of disk IO.

• Assigning more partitions per physical device doesn’t necessarily improve performance.

Subcontext configuration

In the index-type subcontext define

• A mount point for each mounted Flash device. Mount points can be shared across multiple namespaces.

• A mounts-budget (or mounts-size-limit before Database 7.0) directive to indicate this namespace’s share of device storage space available across the given mount points.

• Ensure the budget is less than or equal to the size of the filesystem. If mount points are not shared between namespaces, then simply specify the total available space.

• An optional eviction threshold as a percent of the budget can be defined through evict-mounts-pct (or mounts-high-water-pct before Database 7.0).

Note

In Database 7.0, index-type flash does not work with storing data in PMem (storage-engine pmem) or data in memory (storage-engine memory).

Example

Database 7.0 and later

namespace test {
    partition-tree-sprigs 1M # Typically very large for flash index - see sizing guide.
    index-type flash {
        mounts-budget 1T
        mount /mnt/nvme0 # will have a 250GiB budget
        mount /mnt/nvme1 # will have a 250GiB budget
        mount /mnt/nvme2 # will have a 250GiB budget
        mount /mnt/nvme3 # will have a 250GiB budget
    }
}

Prior to Database 7.0

namespace test {
    partition-tree-sprigs 1M # Typically very large for flash index - see sizing guide.
    index-type flash {
        mount /mnt/nvme0
        mount /mnt/nvme1
        mount /mnt/nvme2
        mount /mnt/nvme3
        mounts-size-limit 1T
    }
}

Capacity planning example

Here is a summary for calculating the disk space and memory required for a namespace with 4 billion records, a replication factor of 2, with the primary index on flash.

Number of sprigs required

• 4 billion records ÷ 4096 partitions ÷ 32 records per sprig, to retain half-fill-factor = ~30,517
• Round up to power of 2: 32,768 sprigs per partition

Disk space required

• 32,768 sprigs per partition × 4096 partitions × 2 replication factor × 4KiB size of each block = 1TiB for the whole cluster
• 1TiB required for the whole cluster ÷ 3 minimal number of nodes ÷ 0.8 with mounts-budget/mounts-size-limit at 80% = 427GiB per node

Because All Flash uses a filesystem with multiple files, the mount point size should be slightly larger than 427GiB (for actual usable index storage space) to accommodate the filesystem overheads. This is filesystem-dependent.

Memory required

With Database 5.7 or later, where 10 bytes are required per sprig:

• 32,768 sprigs per partition × 4096 partitions × 2 replication factor × 10 bytes memory required per sprig = 2,560MiB for the whole cluster
• 2,560MiB required for the whole cluster ÷ 3 minimal number of nodes ÷ 0.8 with mounts-budget/mounts-size-limit at 80% = 1,066MiB per node

Or with server versions prior to 5.7, where 13 bytes are required per sprig:

• 32,768 sprigs per partition × 4096 partitions × 2 replication factor × 13 bytes memory required per sprig = 3,328MiB for the whole cluster
• 3,328MiB required for the whole cluster ÷ 3 minimal number of nodes ÷ 0.8 with mounts-budget/mounts-size-limit at 80% = 1,387MiB per node

Primary index in PMem

When the namespace primary index storage is configured to index-type pmem, Aerospike writes index metadata in multiple files spread across the configured PMem devices. This requires device partitions to be set up with an appropriate filesystem and mounted.

Aerospike requires PMem to be accessible using DAX (Direct Access), that is, using block devices such as /dev/pmem0:

• The NVDIMM regions must be configured as AppDirect regions, as in the following example from a machine with a 750-GiB AppDirect region:

sudo ipmctl show -region
SocketID             ISetID    PersistentMemoryType  Capacity FreeCapacity HealthState
0 0x59727f4821b32ccc               AppDirect        750.0 GiB      0.0 GiB     Healthy

• The NVDIMM regions must be turned into fsdax namespaces, as in the following example from the same machine:

sudo ndctl list
[
  {
    "dev":"namespace0.0",
    "mode":"fsdax",
    "blockdev":"pmem0",
    ...
  }
]

Filesystem configuration

The PMem block device must contain a filesystem that is capable of DAX (Direct Access), such as XFS or ext4. On the machine in the above example, this could be accomplished in the usual way:

Prepare an XFS filesystem

sudo mkfs.xfs -f -d su=2m,sw=1 /dev/pmem0

ext4 filesystem:

sudo mkfs.ext4 /dev/pmem0

Mount the filesystem

Finally, the file system must be mounted with the dax mount option. The dax mount option is important. Without this option, the Linux page cache is involved in all I/O to and from persistent memory, which would drastically reduce performance.

In the following example, we use /mnt/pmem0 as the mount point.

sudo mount -o dax /dev/pmem0 /mnt/pmem0

Remember to make the mount persistent to survive system reboots by adding it to /etc/fstab. The mount point configuration line can be copied from /etc/mtab to /etc/fstab.

Mount point configuration

In the index-type subcontext define

• A mount point for each PMem device. Secondary index metadata will be evenly distributed across all of them. Mount points can be shared across multiple namespaces.

• A mounts-budget (or mounts-size-limit before Database 7.0) directive to indicate this namespace’s share of PMem storage space available across the given mount points.

• Ensure the budget is less than or equal to the size of the filesystem. If mount points are not shared between namespaces, then simply specify the total available space.

• An optional eviction threshold as a percent of the budget can be defined through evict-mounts-pct (or mounts-high-water-pct before Database 7.0). The following configuration snippet extends the above example and makes all of /mnt/pmem0 memory (for example, 750GiB) available to the namespace:

Example

The following configuration snippet extends the earlier example and makes all of /mnt/pmem0 memory (for example, 750 GiB) available to the namespace:

Database 7.0 and later

namespace test {
    index-type pmem {
        mount /mnt/pmem0
        mounts-budget 750G
    }
}

Prior to Database 7.0

namespace test {
    index-type pmem {
        mount /mnt/pmem0
        mounts-size-limit 750G
    }
}

Primary index on Flash

The Aerospike All Flash feature allows primary indexes to be stored on an NVMe SSDs.

This index storage method is typically used for extremely large primary indexes with relatively small records. Accuracy is critical for certain aspects of capacity planning and configuration.

Caution

Cautions

• It is important to understand the subtleties of primary index on flash sizing as scaling up an All Flash namespace may require an increase of partition-tree-sprigs which would require a rolling Cold Restart.

• While it is advisable to adjust the kernel’s min_free_kbytes parameter in any configuration, it is especially important to do so when using primary index on flash. The linux kernel will attempt to make use of all free space by caching disk writes. With primary index on flash configuration, this may result in an out of memory (OOM) kill if there isn’t enough free memory left for normal system operations. For this reason Aerospike recommends setting min_free_kbytes=1153434 (1.1GB). For more information, see Best practices for Aerospike and Linux.

All Flash kernel parameters

Note

The following Linux kernel parameters are required in an All Flash deployment. enforce-best-practices verifies that these kernel parameters have the expected values.

/proc/sys/vm/dirty_bytes = 16777216
/proc/sys/vm/dirty_background_bytes = 1
/proc/sys/vm/dirty_expire_centisecs = 1
/proc/sys/vm/dirty_writeback_centisecs = 10

• When running as non-root, you must prepare these values before running the Aerospike server.
• When running as root, the server configures them automatically.

Either way, if these parameters can’t be correctly set manually, or automatically by the server, the node will not start.

Enable flash index for a namespace

To enable a flash index for a namespace, in the configuration file, add an index-type subsection with an index type of flash to its namespace section. The added index-type subsection must contain:

• One or more mount directives to indicate the mount points on the flash storage to be used for the flash index.

  A single namespace can use flash index storage across multiple mount points and will evenly distribute allocations across all of them.

  Conversely, mount points can be shared across multiple namespaces. The file names underlying namespaces’ flash index allocations are namespace-specific, which avoids file name clashes between namespaces when they share mount points.

• A mounts-budget (or mounts-size-limit before Database 7.0) directive to indicate this namespace’s share of the space available across the given mount points.

  When multiple namespaces share mount points, this configuration directive tells Aerospike how much of the total available memory across mount points each namespace is expected to use.

  Ensure mounts-budget/mounts-size-limit is smaller or equal to the size of the filesystem mount.

  If mount points are not shared between namespaces, then simply specify the total available space.

• The specified value, along with configuration item evict-mounts-pct (or mounts-high-water-pct before Database 7.0), which is disabled by default, forms the basis for calculating the eviction threshold.

Caution

In Database 7.0, index-type flash does not work with storage-engine pmem or storage-engine memory.

Recommended filesystem type - XFS

An XFS file system is recommended because it has been shown to provide better concurrent access to files compared to ext4.

Recommendation for multiple physical devices

Having more physical devices improves performance by increasing parallelism across those. More partitions per physical device doesn’t necessarily improve performance. Aerospike instantiates at least 4 different arena allocations (files) and will allocate more if more devices (logical partitions or physical devices) are present. Instantiating more than 1 arena at a time helps with contention against the same arena, which is important during heavy insertion loads.

Database 7.0 and later

namespace test {
    partition-tree-sprigs 1M # Typically very large for flash index - see sizing guide.
    index-type flash {
        mounts-budget 1T
        mount /mnt/nvme0 # will have a 250GiB budget
        mount /mnt/nvme1 # will have a 250GiB budget
        mount /mnt/nvme2 # will have a 250GiB budget
        mount /mnt/nvme3 # will have a 250GiB budget
    }
}

Prior to Database 7.0

Related documentation

• Queries
• Adding and removing a set index