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Database statistics

Source: R/stat.R
mdbx_env_stat.Rd

Reports the shape of the main database: its page size, B-tree depth, page counts, and how many records it holds.

Usage

mdbx_env_stat(x, ...)

# S3 method for class 'mdbx_txn'
mdbx_env_stat(x, db = NULL, ...)

Arguments

x

An mdbx_env from mdbx_env_open(), or an mdbx_txn from mdbx_txn_begin().

...

Unused, for extensibility.

db

An mdbx_dbi object from mdbx_dbi_open() to report on instead of the main database, or NULL for the main one. Only available when x is a transaction, since a database is resolved within one.

Value

A named list of numbers: pagesize, depth, branch_pages, leaf_pages, overflow_pages, entries (the number of records), and mod_txnid (the transaction that last modified the database). Counts are double because 'libmdbx' reports them as 64-bit integers, which R has no type for; every realistic value is exact.

Details

Passing a transaction reports what that transaction sees, including changes it has made but not committed. Passing the environment reports the same thing whenever this thread holds a transaction, because the environment form reuses it — so uncommitted changes are included, and an abort takes the counts back down.

The two therefore agree in a single-threaded R session. They differ only when a transaction holds a snapshot the environment has moved past, which requires another process to have committed in the meantime.

Without db, the counts cover the whole environment — every named database as well as the main one. Measured, since 'libmdbx' does not say so: a main database of 4 keys plus a named database of 7 reports 11 entries. Pass db for one database's own B-tree.

See also

mdbx_env_info()

Examples

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

mdbx_with_write(env, function(txn) {
  mdbx_put(txn, "a", "1")

  # Counted before the commit.
  mdbx_env_stat(txn)$entries
})
#> [1] 1

mdbx_env_stat(env)$entries
#> [1] 1

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