Runtime Settings

Compatibility Mode KVIKIO_COMPAT_MODE

When KvikIO is running in compatibility mode, it doesn’t load libcufile.so. Instead, reads and writes are done using POSIX. Notice, this is not the same as the compatibility mode in cuFile. It is possible that KvikIO performs I/O in the non-compatibility mode by using the cuFile library, but the cuFile library itself is configured to operate in its own compatibility mode. For more details, refer to cuFile compatibility mode and cuFile environment variables .

The environment variable KVIKIO_COMPAT_MODE has three options (case-insensitive):

  • ON (aliases: TRUE, YES, 1): Enable the compatibility mode.

  • OFF (aliases: FALSE, NO, 0): Disable the compatibility mode, and enforce cuFile I/O. GDS will be activated if the system requirements for cuFile are met and cuFile is properly configured. However, if the system is not suited for cuFile, I/O operations under the OFF option may error out.

  • AUTO: Try cuFile I/O first, and fall back to POSIX I/O if the system requirements for cuFile are not met.

Under AUTO, KvikIO falls back to the compatibility mode:

  • when libcufile.so cannot be found.

  • when running in Windows Subsystem for Linux (WSL).

  • when /run/udev isn’t readable, which typically happens when running inside a docker image not launched with --volume /run/udev:/run/udev:ro.

This setting can also be programmatically accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

Thread Pool KVIKIO_NTHREADS

KvikIO can use multiple threads for IO automatically. Set the environment variable KVIKIO_NTHREADS to the number of threads in the thread pool. If not set, the default value is 1.

This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

Task Size KVIKIO_TASK_SIZE

KvikIO splits parallel IO operations into multiple tasks. Set the environment variable KVIKIO_TASK_SIZE to the maximum task size (in bytes). If not set, the default value is 4194304 (4 MiB).

This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

GDS Threshold KVIKIO_GDS_THRESHOLD

In order to improve performance of small IO, .pread() and .pwrite() implement a shortcut that circumvent the threadpool and use the POSIX backend directly. Set the environment variable KVIKIO_GDS_THRESHOLD to the minimum size (in bytes) to use GDS. If not set, the default value is 16384 (16 KiB).

This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

Size of the Bounce Buffer KVIKIO_BOUNCE_BUFFER_SIZE

KvikIO might have to use intermediate host buffers (one per thread) when copying between files and device memory. Set the environment variable KVIKIO_BOUNCE_BUFFER_SIZE to the size (in bytes) of these “bounce” buffers. If not set, the default value is 16777216 (16 MiB).

This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

HTTP Retries KVIKIO_HTTP_STATUS_CODES, KVIKIO_HTTP_MAX_ATTEMPTS

The behavior when a remote I/O read returns an error can be controlled through the KVIKIO_HTTP_STATUS_CODES, KVIKIO_HTTP_MAX_ATTEMPTS, and KVIKIO_HTTP_TIMEOUT environment variables.

KvikIO will retry a request should any of the HTTP status code in KVIKIO_HTTP_STATUS_CODES is received. The default values are 429, 500, 502, 503, 504. This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

The maximum number of attempts to make before throwing an exception is controlled by KVIKIO_HTTP_MAX_ATTEMPTS. The default value is 3. This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

The maximum duration of each HTTP request is controlled by KVIKIO_HTTP_TIMEOUT. The default value is 60, which is the duration in seconds to allow. This setting can also be accessed using kvikio.defaults.get() (getter) and kvikio.defaults.set() (setter).

HTTP Verbose KVIKIO_REMOTE_VERBOSE

For debugging HTTP requests, you can enable verbose output that shows detailed information about HTTP communication including headers, request/response bodies, connection details, and SSL handshake information.

Set the environment variable KVIKIO_REMOTE_VERBOSE to true, on, yes, or 1 (case-insensitive) to enable verbose output. Otherwise, verbose output is disabled by default.

Warning

This may show sensitive contents from headers and data.

CA bundle file and CA directory CURL_CA_BUNDLE, SSL_CERT_FILE, SSL_CERT_DIR

The Certificate Authority (CA) paths required for TLS/SSL verification in libcurl can be explicitly specified using the following environment variables in order of overriding priority:

  • CURL_CA_BUNDLE (also used in the curl program) or SSL_CERT_FILE (also used in OpenSSL): Specifies the CA certificate bundle file location.

  • SSL_CERT_DIR (also used in OpenSSL): Specifies the CA certificate directory.

When neither is specified, KvikIO searches several standard system locations for the CA file and directory, and if the search fails falls back to the libcurl compile-time defaults.

Opportunistic POSIX Direct I/O operations KVIKIO_AUTO_DIRECT_IO_READ, KVIKIO_AUTO_DIRECT_IO_WRITE

Overview

By default, POSIX I/O operations perform buffered I/O using the OS page cache. However, Direct I/O (bypassing the page cache) can significantly improve performance in certain scenarios, such as writes and cold page-cache reads.

Traditional Direct I/O has strict requirements: The buffer address must be page-aligned, the file offset must be page-aligned, and the transfer size must be a multiple of page size (typically 4096 bytes). kvikio.CuFile provides the feature of opportunistic Direct I/O, which removes these restrictions by automatically handling alignment. Specifically, KvikIO can split a POSIX I/O operation into unaligned and aligned segments and apply buffered I/O and direct I/O respectively.

Configuration

Set the environment variable KVIKIO_AUTO_DIRECT_IO_READ / KVIKIO_AUTO_DIRECT_IO_WRITE to true, on, yes, or 1 (case-insensitive) to enable opportunistic Direct I/O.

export KVIKIO_AUTO_DIRECT_IO_READ=1
export KVIKIO_AUTO_DIRECT_IO_WRITE=1

Set them to false, off, no, or 0 to disable this feature and use buffered I/O.

export KVIKIO_AUTO_DIRECT_IO_READ=0
export KVIKIO_AUTO_DIRECT_IO_WRITE=0

If not set, the default setting is buffered I/O for POSIX read (KVIKIO_AUTO_DIRECT_IO_READ=0) and Direct I/O for POSIX write (KVIKIO_AUTO_DIRECT_IO_WRITE=1).

Programmatic Access

These settings can be queried (kvikio.defaults.get()) and modified (kvikio.defaults.set()) at runtime using the property name auto_direct_io_read and auto_direct_io_write.

Example:

import kvikio.defaults

# Check current settings
print(kvikio.defaults.get("auto_direct_io_read"))
print(kvikio.defaults.get("auto_direct_io_write"))

# Enable Direct I/O for reads, and disable it for writes
kvikio.defaults.set({"auto_direct_io_read": True, "auto_direct_io_write": False})