tcl-lmdb

This is the Lightning Memory-Mapped Database (LMDB) extension for Tcl using the Tcl Extension Architecture (TEA).

LMDB is a Btree-based database management library with an API similar to BerkeleyDB. The library is thread-aware and supports concurrent read/write access from multiple processes and threads. The DB structure is multi-versioned, and data pages use a copy-on-write strategy, which also provides resistance to corruption and eliminates the need for any recovery procedures. The database is exposed in a memory map, requiring no page cache layer of its own.

For additional information on LMDB see

https://www.symas.com/symas-embedded-database-lmdb

License

LMDB is Licensed under the OpenLDAP, Public License.
tcl-lmdb is Licensed under the 2-Clause BSD license.

Documents

• LMDB Source code
• LMDB C API reference

UNIX BUILD

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.

$ cd tcl-lmdb
$ ./configure --prefix=/opt/tcl
$ make
$ make install

If you need setup directory containing tcl configuration (tclConfig.sh), below is an example:

$ cd tcl-lmdb
$ ./configure --with-tcl=/opt/activetcl/lib
$ make
$ make install

If your Linux distribution (ex. Debian, Ubuntu, Fedora, and OpenSuSE) includes LMDB, tcl-lmdb support to use the system shared library for LMDB.

Below is an example:

$ ./configure --with-system-lmdb=yes

WINDOWS BUILD

The recommended method to build extensions under windows is to use the Msys + Mingw build process. This provides a Unix-style build while generating native Windows binaries. Using the Msys + Mingw build tools means that you can use the same configure script as per the Unix build to create a Makefile.

Implement commands

The key and data is interpreted by Tcl as a string.

(Or a byte array, depends on what command you use. And if you use byte array related command, please use it carefully.)

Basic usage

lmdb version ?-string?

The command lmdb version return a list of the form {major minor patch} for the major, minor and patch levels of the LMDB release. -string return a string with LMDB version information.

Database Environment

lmdb env
env_handle open -path path ?-mode mode? ?-fixedmap BOOLEAN? ?-nosubdir BOOLEAN? ?-readonly BOOLEAN? ?-nosync BOOLEAN? ?-nordahead BOOLEAN?
env_handle set_mapsize size
env_handle set_maxreaders nReaders
env_handle set_maxdbs nDbs
env_handle sync force
env_handle stat
env_handle copy path ?-cp_compact boolean?
env_handle get_path
env_handle get_maxreaders
env_handle get_maxkeysize
env_handle close

The lmdb env create an environment handle env_handle. The returned environment handle is bound to a Tcl command of the form envN, where N is an integer starting at 0 (for example, env0 and env1).

The env_handle open open an environment handle. The path is the directory in which the database files reside. This directory must already exist and be writable. The mode is the UNIX permissions to set on created files and semaphores. This parameter is ignored on Windows. -nosync flag setup don't flush system buffers to disk when committing a transaction.

By default, LMDB creates its environment in a directory whose pathname is given in path, and creates its data and lock files under that directory. With -nosubdir this option, path is used as-is for the database main data file. The database lock file is the path with "-lock" appended.

-nordahead this option turn off readahead. Most operating systems perform readahead on read requests by default. This option turns it off if the OS supports it. Turning it off may help random read performance when the DB is larger than RAM and system RAM is full. The option is not implemented on Windows.

The env_handle set_mapsize size set the size of the memory map to use for this environment. Default size of memory map is 10485760. Apps should always set the size explicitly using env_handle set_mapsize to setup size of the memory map.

The env_handle set_maxdbs set the maximum number of named databases for the environment. This command is only needed if multiple databases will be used in the environment. Simpler applications that use the environment as a single unnamed database can ignore this option. This function may only be called after lmdb env and before env_handle open command.

The env_handle sync flush the data buffers to disk. force is non-zero, force a synchronous flush. 0 do nothing. Data is always written to disk when is called, but the operating system may keep it buffered. LMDB always flushes the OS buffers upon commit as well, unless the environment was opened with -nosync. This command returns 0 on success, and in the case of error, a Tcl error is thrown.

The env_handle copy copy an LMDB environment to the specified path. -cp_compact perform compaction while copying (-cp_compact option only work when LMDB version > 0.9.13). This command returns 0 on success, and in the case of error, a Tcl error is thrown.

The env_handle stat return statistics list about the LMDB environment.

The env_handle get_maxreaders get the maximum number of threads/reader slots for the environment.

The env_handle get_maxkeysize get the maximum size of keys and -dupsort data we can write. Default 511.

The env_handle close command close the environment and release the memory map. This command returns 0 on success, and in the case of error, a Tcl error is thrown.

Database

lmdb open -env env_handle ?-name database? ?-reversekey BOOLEAN? ?-dupsort BOOLEAN? ?-dupfixed BOOLEAN? ?-reversedup BOOLEAN? ?-create BOOLEAN?
dbi_handle put key data -txn txnid ?-nodupdata boolean? ?-nooverwrite boolean? ?-append boolean? ?-appenddup boolean?
dbi_handle get key -txn txnid
dbi_handle del key data -txn txnid
dbi_handle putBinary key data -txn txnid ?-nodupdata boolean? ?-nooverwrite boolean? ?-append boolean? ?-appenddup boolean?
dbi_handle getBinary key -txn txnid
dbi_handle delBinary key data -txn txnid
dbi_handle drop del_flag -txn txnid
dbi_handle stat -txn txnid
dbi_handle close -env env_handle

The command lmdb open create a database handle. -name database is the name of the database to open option. If only a single database is needed in the environment, skip to setup database name (or you need use env_handle set_maxdbs to set the maximum number of named databases for the environment).

-dupsort let duplicate keys may be used in the database. (Or, from another perspective, keys may have multiple data items, stored in sorted order.) By default keys must be unique and may have only a single data item. -dupfixed may only be used in combination with -dupsort, sorted dup items have fixed size.

-create to create the named database if it doesn't exist. This option is not allowed in a read-only transaction or a read-only environment. The returned database handle is bound to a Tcl command of the form dbiN, where N is an integer starting at 0 (for example, dbi0 and dbi1).

The command dbi_handle get get items from a database. If the database supports duplicate keys -dupsort then the first data item for the key will be returned. Retrieval of other items requires the use of cursor_handle get.

The command dbi_handle put store items into a database. -nodupdata may only be specified if the database was opened with -dupsort. -nooverwrite enter the new key/data pair only if the key does not already appear in the database. -append is given key/data pair to the end of the database. -appenddup as -append, but for sorted dup data.

The command dbi_handle del delete items from a database. If the database supports sorted duplicates and the data parameter is "" (empty string), all of the duplicate data items for the key will be deleted. Otherwise, if the data parameter is non-NULL only the matching data item will be deleted.

The command dbi_handle drop empty or delete+close a database. del_flag setup 0 to empty the DB, 1 to delete it from the environment and close the DB handle.

The command dbi_handle stat return statistics list for a database.

The dbi_handle close command close a database handle.

Transactions

env_handle txn ?-parent txnid? ?-readonly boolean?
txn_handle abort
txn_handle commit
txn_handle reset
txn_handle renew
txn_handle close

The command env_handle txn create a transaction for use with the environment. -parent txnid please notice: nested transactions max 1 child, write txns only. -readonly this transaction will not perform any write operations. The returned transaction handle is bound to a Tcl command of the form env.txnX, where X is an integer starting at 0 (for example, env0.txn0 and env0.txn1).

The command txn_handle reset reset a read-only transaction. Abort the transaction like txn_handle abort, but keep the transaction handle.

txn_handle renew may reuse the handle. This command returns 0 on success, and in the case of error, a Tcl error is thrown.

txn_handle close command close a transaction handle.

Cursor

dbi_handle cursor -txn txnid
cursor_handle get ?-current? ?-first? ?-firstdup? ?-last? ?-lastdup? ?-next? ?-nextdup? ?-nextnodup? ?-prev? ?-prevdup? ?-prevnodup?
cursor_handle get -set key
cursor_handle get -set_range key
cursor_handle get -get_multiple key data
cursor_handle get -next_multiple key data
cursor_handle get -get_both key data
cursor_handle get -get_both_range key data
cursor_handle put key data ?-current boolean? ?-nodupdata boolean? ?-nooverwrite boolean? ?-append boolean? ?-appenddup boolean?
cursor_handle getBinary ?-current? ?-first? ?-firstdup? ?-last? ?-lastdup? ?-next? ?-nextdup? ?-nextnodup? ?-prev? ?-prevdup? ?-prevnodup?
cursor_handle getBinary -set key
cursor_handle getBinary -set_range key
cursor_handle getBinary -get_multiple key data
cursor_handle getBinary -next_multiple key data
cursor_handle getBinary -get_both key data
cursor_handle getBinary -get_both_range key data
cursor_handle putBinary key data ?-current boolean? ?-nodupdata boolean? ?-nooverwrite boolean? ?-append boolean? ?-appenddup boolean?
cursor_handle del ?-nodupdata boolean?
cursor_handle renew -txn txnid
cursor_handle count
cursor_handle close

The dbi_handle cursor command creates a database cursor. The returned cursor handle is bound to a Tcl command of the form dbiN.cX, where X is an integer starting at 0 (for example, dbi0.c0 and dbi0.c1).

The cursor_handle get command returns a list of {key value} pairs. -firstdup, -lastdup, -nextnodup, -prevdup and -get_both only for -dupsort. -set is position at specified key.

-set_range is position at first key greater than or equal to specified key.

-get_multiple return key and up to a page of duplicate data items from current cursor position. Move cursor to prepare for -next_multiple. Only for -dupfixed.

-next_multiple return key and up to a page of duplicate data items from next cursor position. Only for -dupfixed.

-get_both is position at key/data pair. Only for -dupsort. -get_both_range is position at key, nearest data. Only for -dupsort.

The cursor_handle put command stores key/data pairs into the database.

-current replace the item at the current cursor position. The key parameter must still be provided, and must match it. If using sorted duplicates (-dupsort) the data item must still sort into the same place.

-nodupdata may only be specified if the database was opened with -dupsort.

-nooverwrite enter the new key/data pair only if the key does not already appear in the database.

-append is given key/data pair to the end of the database. No key comparisons are performed.

-appenddup as -append, but for sorted dup data.

This command returns 0 on success, and in the case of error, a Tcl error is thrown.

The cursor_handle del command deletes the key/data pair to which the cursor refers. This command returns 0 on success, and in the case of error, a Tcl error is thrown.

The cursor_handle renew command renew a cursor handle. A cursor is associated with a specific transaction and database. Cursors that are only used in read-only transactions may be re-used, to avoid unnecessary malloc/free overhead. The cursor may be associated with a new read-only transaction, and referencing the same database handle as it was created with. This may be done whether the previous transaction is live or dead.

The cursor_handle count command return count of duplicates for current key. This command is only valid on databases that support sorted duplicate data items -dupsort.

The cursor_handle close command close a cursor handle.

Examples

Get LMDB version

package require lmdb

set version [lmdb version -string]
puts "LMDB version is $version"

Create Env and get basic info

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
$myenv set_maxreaders 127
file mkdir "testdb"
$myenv open -path "testdb"
set mydbi [lmdb open -env $myenv]

puts [$myenv get_path]
puts [$myenv get_maxreaders]
puts [$myenv get_maxkeysize]

file mkdir "test.db"
# Copy an LMDB environment to the specified path
$myenv copy "test.db"

puts "Check current stat:"
set stat [$myenv stat]
puts "ms_psize: [lindex $stat 0]"
puts "ms_depth: [lindex $stat 1]"
puts "ms_branch_pages: [lindex $stat 2]"
puts "ms_leaf_pages: [lindex $stat 3]"
puts "ms_overflow_pages: [lindex $stat 4]"
puts "ms_entries: [lindex $stat 5]"

$mydbi close -env $myenv
$myenv close
exit

Put and get data

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
file mkdir "testdb"

if {[catch {$myenv open -path "testdb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv]

set mytxn [$myenv txn]
for {set i 1} {$i < 1000} {incr i} {
    $mydbi put $i $i -txn $mytxn
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
for {set i 1} {$i < 1000} {incr i} {
puts [$mydbi get $i -txn $mytxn2]
}
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Put and get data (nosubdir case, for v0.2.4)

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824

if {[catch {$myenv open -path "mytestdb" -nosubdir 1} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv]

set mytxn [$myenv txn]
for {set i 1000} {$i < 5000} {incr i} {
    $mydbi put $i $i -txn $mytxn
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
for {set i 1000} {$i < 5000} {incr i} {
puts [$mydbi get $i -txn $mytxn2]
}
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Put and get a file

package require lmdb

set filename "lmdb-mdb.master.zip"
set size [file size "/home/danilo/Downloads/lmdb-mdb.master.zip"] 
set fd [open "/home/danilo/Downloads/lmdb-mdb.master.zip" {RDWR BINARY}]
fconfigure $fd -blocking 1 -translation binary 
set data [read $fd $size]
close $fd  

set myenv [lmdb env]
$myenv set_mapsize 1073741824
file mkdir "testdb"

if {[catch {$myenv open -path "testdb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv]

set mytxn [$myenv txn]
$mydbi put $filename $data -txn $mytxn
$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
set fetch_data [$mydbi get $filename -txn $mytxn2]
set fd [open "/home/danilo/Downloads/lmdb-mdb.master_test.zip" {CREAT RDWR BINARY}]  
fconfigure $fd -blocking 1 -translation binary 
puts -nonewline $fd $fetch_data  
close $fd
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close

Cursor

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
file mkdir "testdb"

if {[catch {$myenv open -path "testdb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv]

set mytxn [$myenv txn]
for {set i 1} {$i < 1000} {incr i} {
    $mydbi put $i $i -txn $mytxn
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
set mycursor [$mydbi cursor -txn $mytxn2]

while { [catch {set data [$mycursor get -next]} result] == 0} {   
    puts $data
}

$mycursor close
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Cursor (dupsort)

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
$myenv set_maxdbs 10
file mkdir "testdb"

if {[catch {$myenv open -path "testdb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv -name "testdb" -dupsort 1 -create 1]

set mytxn [$myenv txn]
for {set i 1} {$i < 1000} {incr i} {
for {set j 1} {$j < 10} {incr j} {
    $mydbi put $i $j -txn $mytxn
}
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
set mycursor [$mydbi cursor -txn $mytxn2]

while { [catch {set data [$mycursor get -nextnodup]} result] == 0} {   
    puts $data
    set number [$mycursor count]       
    for {set num 0} {$num < $number} {incr num} {
    if { [catch {set data [$mycursor get -nextdup]} result] == 0 } {
        puts $data
    }
    }
}

$mycursor close
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Cursor (dupfixed, for 0.3.1)

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
$myenv set_maxdbs 10
file mkdir "fixeddb"

if {[catch {$myenv open -path "fixeddb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv -name "fixeddb" \
                     -dupsort 1 -dupfixed 1 -create 1]

set mytxn [$myenv txn]
for {set i 1} {$i < 10} {incr i} {
for {set j 1} {$j < 20} {incr j} {
    set value [format "%07x" $j]
    $mydbi put $i $value -txn $mytxn
}
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
set mycursor [$mydbi cursor -txn $mytxn2]

while { [catch {set data [$mycursor get -nextnodup]} result] == 0} {
    puts $data
    set number [$mycursor count]
    for {set num 0} {$num < $number} {incr num} {
    if { [catch {set data [$mycursor get -nextdup]} result] == 0 } {
        puts $data
    }
    }
}

$mycursor close
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Cursor (-get_multiple and -next_multiple, for 0.3.2)

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
$myenv set_maxdbs 10
file mkdir "fixeddb"

if {[catch {$myenv open -path "fixeddb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv -name "myfixeddb" \
                    -dupsort 1 -dupfixed 1 -create 1]

set mytxn [$myenv txn]
for {set i 1} {$i < 20} {incr i} {
    for {set j 1} {$j < 20} {incr j} {
        set key [format "%04d" $i]
        set value [format "%08d" [expr $j * $j]]
        $mydbi put $key $value -txn $mytxn
    }
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn]
set mycursor [$mydbi cursor -txn $mytxn2]

set data [$mycursor get -first]
set key [lindex $data 0]
set value [lindex $data 1]

# -get_multiple return key and up to a page of duplicate data items
# from current cursor position
set data [$mycursor get -get_multiple $key $value]
set key [lindex $data 0]
puts "key is $key"
puts "=========="
set value [lindex $data 1]

# parse value string (all in a string)
set length [expr [string length $value] / 8]
for {set index 0} {$index < $length} {incr index 1} {
    set sub_value [string range $value [expr $index * 8] [expr $index * 8 + 7]]
    puts $sub_value
}

while { [catch {set data [$mycursor get -nextnodup]} result] == 0} {
    # -next_multiple return key and up to a page of duplicate data items
    # from next cursor position
    set data [$mycursor get -next_multiple $key $value]
    set key [lindex $data 0]
    puts "key is $key"
    puts "=========="
    set value [lindex $data 1]

    set length [expr [string length $value] / 8]
    for {set index 0} {$index < $length} {incr index 1} {
        set sub_value [string range $value [expr $index * 8] [expr $index * 8 + 7]]
        puts $sub_value
    }

    puts "=========="
}

$mycursor close
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit

Cursor and Transaction

package require lmdb

set myenv [lmdb env]
$myenv set_mapsize 1073741824
file mkdir "testdb"

if {[catch {$myenv open -path "testdb"} error] != 0} {
    puts "open database fail: $error"
    $myenv close
    exit
}

set mydbi [lmdb open -env $myenv]

set mytxn [$myenv txn]
for {set i 1} {$i <= 1000} {incr i} {
    $mydbi put $i $i -txn $mytxn
}

$mytxn commit
$mytxn close

set mytxn2 [$myenv txn -readonly 1]
set mycursor [$mydbi cursor -txn $mytxn2]

while { [catch {set data [$mycursor get -next]} result] == 0} {   
    puts $data
}

$mytxn2 reset
$mytxn2 renew
$mycursor renew -txn $mytxn2

set data [$mycursor get -last]
while { [catch {set data [$mycursor get -prev]} result] == 0} {   
    puts $data
}

$mycursor close
$mytxn2 abort
$mytxn2 close

$mydbi close -env $myenv
$myenv close
exit 

Thread (for v0.2.3)

package require Thread

set t1 [thread::create]
thread::send $t1 {
    package require lmdb
    set myenv [lmdb env]
    $myenv set_mapsize 268435456
    $myenv set_maxdbs 10
    file mkdir "testdb"

    if {[catch {$myenv open -path "testdb"} error] != 0} {
        puts "open database fail: $error"
        $myenv close
        exit
    }    
    set mydbi [lmdb open -env $myenv -name "testdb" -create 1]
}

thread::send $t1 {
    set mytxn [$myenv txn]
    for {set i 1} {$i < 10} {incr i} {
        $mydbi put $i $i -txn $mytxn
    }

    $mytxn commit
    $mytxn close

    set mytxn2 [$myenv txn -readonly 1]
    for {set i 1} {$i < 10} {incr i} {
        puts [$mydbi get $i -txn $mytxn2]
    }
    $mytxn2 abort
    $mytxn2 close
}

thread::send $t1 {
    set mytxn [$myenv txn]
    $mydbi put foo bar -txn $mytxn
    $mytxn commit
    $mytxn close
}

set t2 [thread::create]
thread::send $t2 {
    package require lmdb
    set myenv [lmdb env]
    $myenv set_mapsize 268435456
    $myenv set_maxdbs 10
    file mkdir "testdb"

    # The default flag setup -fixedmap to 1.
    # However, if you use other thread and the same env,
    # please setup -fixedmap to 0 (still need test)
    # or LMDB return ERROR: Device or resource busy   
    if {[catch {$myenv open -path "testdb" -fixedmap 0} error] != 0} {
        puts "open database fail: $error"
        $myenv close
        exit
    }           
    set dbi [lmdb open -env $myenv -name "testdb2" -create 1]
}

thread::send $t1 {
    set mytxn2 [$myenv txn -readonly 1]
    puts [$mydbi get foo -txn $mytxn2]
    $mytxn2 abort
    $mytxn2 close
}

thread::send $t2 {
    set mytxn [$myenv txn]
    for {set i 1} {$i < 10} {incr i} {
        $dbi put $i $i -txn $mytxn
    }

    $mytxn commit
    $mytxn close

    set mytxn2 [$myenv txn -readonly 1]
    for {set i 1} {$i < 10} {incr i} {
        puts [$dbi get $i -txn $mytxn2]
    }
    $mytxn2 abort
    $mytxn2 close
}

thread::send $t1 {
$mydbi close -env $myenv
$myenv close
}

thread::send $t2 {
$dbi close -env $myenv
$myenv close
}

exit