Size limits imposed by 'libmdbx'

Reports the largest key, value and database 'libmdbx' will accept. Most of these follow from the page size, which is why they are worth asking about rather than assuming: the maximum key is a little under half a page, so it is 8166 bytes where pages are 16 KB and 2022 bytes where they are 4 KB. Code that hardcodes a size works on one machine and fails on another.

Usage

mdbx_limits(x = NULL)

Arguments

x

What to report limits for. An mdbx_env or mdbx_txn uses that database's actual page size — usually what you want. A single number is treated as a page size, for asking about a platform you are not on. NULL, the default, uses this system's default page size.

Value

A named list of numbers: pagesize, keysize_min, keysize_max, valsize_min, valsize_max, dbsize_min, dbsize_max and txnsize_max, all in bytes. keysize_min and valsize_min are zero, which is how an empty key and an empty value are both legal.

See also

mdbx_env_stat(), which reports the page size in use.

Examples

# This system's defaults.
mdbx_limits()$keysize_max
#> [1] 2022

# The same question for a machine with 4 KB pages.
mdbx_limits(4096)$keysize_max
#> [1] 2022

path <- tempfile(fileext = ".mdbx")
env <- mdbx_env_open(path)

# The limits that actually apply to this database.
limits <- mdbx_limits(env)
limits$keysize_max
#> [1] 2022

mdbx_env_close(env)
unlink(c(path, paste0(path, "-lck")))