LevelDB is a fast key-value storage library written at Google that provides an ordered mapping from string keys to string values.
This extension is the Tcl interface to the LevelDB.
LevelDB is Licensed under New BSD License.
tcl-leveldb is Licensed under MIT License.
I only test on openSUSE LEAP 42.3/15.0 and Ubuntu 14.04.
openSUSE LEAP 42.3 install leveldb development files:
sudo zypper install leveldb-devel
Ubuntu 14.04 install leveldb development files:
sudo apt-get install libleveldb-dev
After install LevelDB shared library, you can build this extension.
Building under most UNIX systems is easy, just run the configure script and then run make. For more information about the build process, see the tcl/unix/README file in the Tcl src dist. The following minimal example will install the extension in the /opt/tcl directory.
$ export CC=g++
$ cd tcl-leveldb
$ ./configure --prefix=/opt/tcl
$ make
$ make install
If you need setup directory containing tcl configuration (tclConfig.sh), below is an example:
$ export CC=g++
$ cd tcl-leveldb
$ ./configure --with-tcl=/opt/activetcl/lib
$ make
$ make install
The key and data is interpreted by Tcl as a string.
leveldb version
The command leveldb version return a list of the form {major minor}
for the major and minor levels of the LevelDB release.
leveldb open -path path ?-create_if_missing BOOLEAN? ?-error_if_exists BOOLEAN?
?-paranoid_checks BOOLEAN? ?-write_buffer_size size? ?-max_open_files number?
?-block_size size? ?-compression type?
leveldb repair name
leveldb destroy name
DB_HANDLE get key ?-fillCache BOOLEAN? ?-snapshot HANDLE?
DB_HANDLE put key value ?-sync BOOLEAN?
DB_HANDLE delete key ?-sync BOOLEAN?
DB_HANDLE write BAT_HANDLE
DB_HANDLE batch
DB_HANDLE iterator ?-snapshot HANDLE?
DB_HANDLE snapshot
DB_HANDLE getApproximateSizes start limit
DB_HANDLE getProperty property
DB_HANDLE close
IT_HANDLE seektofirst
IT_HANDLE seektolast
IT_HANDLE seek key
IT_HANDLE valid
IT_HANDLE next
IT_HANDLE prev
IT_HANDLE key
IT_HANDLE value
IT_HANDLE close
BAT_HANDLE put key value
BAT_HANDLE delete key
BAT_HANDLE close
SNAPSHOT_HANDLE close -db DB_HANDLE
The command leveldb open create a database handle. -path option is the path
of the database to open. -compression type supports "no" and "snappy".
(Please link to snappy, I think it is the default type.)
If a DB cannot be opened, you may attempt to call leveldb repair this method
to resurrect as much of the contents of the database as possible. Some data
may be lost, so be careful when calling this function on a database that
contains important information.
leveldb destroy destroy the contents of the specified database.
Be very careful using this method.
DB_HANDLE batch create a WriteBatch handle. Users can use DB_HANDLE write
to apply a set of updates.
DB_HANDLE iterator create an Iterator handle.
DB_HANDLE snapshot created a Snapshot handle. Snapshots provide consistent
read-only views over the entire state of the key-value store.
DB_HANDLE getApproximateSizes can used to get the approximate number of
bytes.
DB_HANDLE getProperty can get DB export properties about their state via
this method. If it is a valid property, returns its current value.
A basic example:
package require leveldb
set dbi [leveldb open -path "./testdb" -create_if_missing 1]
$dbi put "test1" "1234567890"
set value [$dbi get "test1"]
puts $value
$dbi delete "test1"
$dbi put "test2" "2345678901"
$dbi put "test3" "3456789010"
$dbi put "test4" "4567890102"
$dbi put "test5" "5678901023"
set it [$dbi iterator]
for {$it seektofirst} {[$it valid] == 1} {$it next} {
set key [$it key]
set value [$it value]
puts "Iterator --- I get $key: $value"
}
$it close
$dbi close
WriteBatch example:
package require leveldb
set dbi [leveldb open -path "./testdb" -create_if_missing 1]
set bat [$dbi batch]
$bat put "test1" "1234567890"
$bat put "test2" "2345678901"
$bat put "test3" "3456789010"
$bat put "test4" "4567890102"
$bat put "test5" "5678901023"
$dbi write $bat
$bat close
set it [$dbi iterator]
for {$it seektofirst} {[$it valid] == 1} {$it next} {
set key [$it key]
set value [$it value]
puts "Iterator --- I get $key: $value"
}
$it close
$dbi close
Snapshot example:
package require leveldb
set dbi [leveldb open -path "./testdb" -create_if_missing 1 \
-block_size 1024 -compression snappy]
$dbi put "test1" "1234567890"
$dbi put "test2" "2345678901"
$dbi put "test3" "3456789010"
$dbi put "test4" "4567890102"
$dbi put "test5" "5678901023"
set snapshot [$dbi snapshot]
$dbi put "test1" "It is the world after snapshot!!!"
# get
set value [$dbi get "test1" -snapshot $snapshot]
puts "Is is snapshot version: $value"
set value [$dbi get "test1"]
puts "Is is current version: $value"
# Iterator
puts "It is snapshot version:"
set it [$dbi iterator -snapshot $snapshot]
for {$it seektofirst} {[$it valid] == 1} {$it next} {
set key [$it key]
set value [$it value]
puts "Iterator --- I get $key: $value"
}
$it close
puts "It is current version:"
set it [$dbi iterator]
for {$it seektofirst} {[$it valid] == 1} {$it next} {
set key [$it key]
set value [$it value]
puts "Iterator --- I get $key: $value"
}
$it close
$snapshot close -db $dbi
$dbi close