Class TokyoCabinet::BDB
In: tokyocabinet-doc.rb
Parent: Object

B+ tree database is a file containing a B+ tree and is handled with the B+ tree database API. Before operations to store or retrieve records, it is necessary to open a database file and connect the B+ tree database object to it. To avoid data missing or corruption, it is important to close every database file when it is no longer in use. It is forbidden for multible database objects in a process to open the same database at the same time.
Except for the interface below, methods compatible with the `Hash' class are also provided; `[]', `[]=', `store', `delete', `fetch', `has_key?', `has_value?', `key', `clear', `length', `empty?', `each', `each_key', `each_value', and `keys'.

Methods

adddouble   addint   close   copy   ecode   errmsg   fsiz   fwmkeys   get   getlist   new   open   optimize   out   outlist   path   put   putcat   putdup   putkeep   putlist   range   rnum   setcache   setcmpfunc   setdfunit   setxmsiz   sync   tranabort   tranbegin   trancommit   tune   vanish   vnum   vsiz  

Constants

ESUCCESS = 0   error code: success
ETHREAD = 1   error code: threading error
EINVALID = 2   error code: invalid operation
ENOFILE = 3   error code: file not found
ENOPERM = 4   error code: no permission
EMETA = 5   error code: invalid meta data
ERHEAD = 6   error code: invalid record header
EOPEN = 7   error code: open error
ECLOSE = 8   error code: close error
ETRUNC = 9   error code: trunc error
ESYNC = 10   error code: sync error
ESTAT = 11   error code: stat error
ESEEK = 12   error code: seek error
EREAD = 13   error code: read error
EWRITE = 14   error code: write error
EMMAP = 15   error code: mmap error
ELOCK = 16   error code: lock error
EUNLINK = 17   error code: unlink error
ERENAME = 18   error code: rename error
EMKDIR = 19   error code: mkdir error
ERMDIR = 20   error code: rmdir error
EKEEP = 21   error code: existing record
ENOREC = 22   error code: no record found
EMISC = 9999   error code: miscellaneous error
CMPLEXICAL = "CMPLEXICAL"   comparison function: by lexical order
CMPDECIMAL = "CMPDECIMAL"   comparison function: as decimal strings of real numbers
CMPINT32 = "CMPINT32"   comparison function: as 32-bit integers in the native byte order
CMPINT64 = "CMPINT64"   comparison function: as 64-bit integers in the native byte order
TLARGE = 1 << 0   tuning option: use 64-bit bucket array
TDEFLATE = 1 << 1   tuning option: compress each record with Deflate
TBZIP = 1 << 2   tuning option: compress each record with BZIP2
TTCBS = 1 << 3   tuning option: compress each record with TCBS
OREADER = 1 << 0   open mode: open as a reader
OWRITER = 1 << 1   open mode: open as a writer
OCREAT = 1 << 2   open mode: writer creating
OTRUNC = 1 << 3   open mode: writer truncating
ONOLCK = 1 << 4   open mode: open without locking
OLCKNB = 1 << 5   open mode: lock without blocking
OTSYNC = 1 << 6   open mode: synchronize every transaction

Public Class methods

new()

Create a B+ tree database object.
The return value is the new B+ tree database object.

Public Instance methods

adddouble(key, num)

Add a real number to a record.
`key' specifies the key.
`num' specifies the additional value.
If successful, the return value is the summation value, else, it is `nil'.
If the corresponding record exists, the value is treated as a real number and is added to. If no record corresponds, a new record of the additional value is stored. Because records are stored in binary format, they should be processed with the `unpack' method with the `d' operator after retrieval.

addint(key, num)

Add an integer to a record.
`key' specifies the key.
`num' specifies the additional value.
If successful, the return value is the summation value, else, it is `nil'.
If the corresponding record exists, the value is treated as an integer and is added to. If no record corresponds, a new record of the additional value is stored. Because records are stored in binary format, they should be processed with the `unpack' method with the `i' operator after retrieval.

close()

Close the database file.
If successful, the return value is true, else, it is false.
Update of a database is assured to be written when the database is closed. If a writer opens a database but does not close it appropriately, the database will be broken.

copy(path)

Copy the database file.
`path' specifies the path of the destination file. If it begins with `@', the trailing substring is executed as a command line.
If successful, the return value is true, else, it is false. False is returned if the executed command returns non-zero code.
The database file is assured to be kept synchronized and not modified while the copying or executing operation is in progress. So, this method is useful to create a backup file of the database file.

ecode()

Get the last happened error code.
The return value is the last happened error code.
The following error codes are defined: `TokyoCabinet::BDB::ESUCCESS' for success, `TokyoCabinet::BDB::ETHREAD' for threading error, `TokyoCabinet::BDB::EINVALID' for invalid operation, `TokyoCabinet::BDB::ENOFILE' for file not found, `TokyoCabinet::BDB::ENOPERM' for no permission, `TokyoCabinet::BDB::EMETA' for invalid meta data, `TokyoCabinet::BDB::ERHEAD' for invalid record header, `TokyoCabinet::BDB::EOPEN' for open error, `TokyoCabinet::BDB::ECLOSE' for close error, `TokyoCabinet::BDB::ETRUNC' for trunc error, `TokyoCabinet::BDB::ESYNC' for sync error, `TokyoCabinet::BDB::ESTAT' for stat error, `TokyoCabinet::BDB::ESEEK' for seek error, `TokyoCabinet::BDB::EREAD' for read error, `TokyoCabinet::BDB::EWRITE' for write error, `TokyoCabinet::BDB::EMMAP' for mmap error, `TokyoCabinet::BDB::ELOCK' for lock error, `TokyoCabinet::BDB::EUNLINK' for unlink error, `TokyoCabinet::BDB::ERENAME' for rename error, `TokyoCabinet::BDB::EMKDIR' for mkdir error, `TokyoCabinet::BDB::ERMDIR' for rmdir error, `TokyoCabinet::BDB::EKEEP' for existing record, `TokyoCabinet::BDB::ENOREC' for no record found, and `TokyoCabinet::BDB::EMISC' for miscellaneous error.

errmsg(ecode)

Get the message string corresponding to an error code.
`ecode' specifies the error code. If it is not defined or negative, the last happened error code is specified.
The return value is the message string of the error code.

fsiz()

Get the size of the database file.
The return value is the size of the database file or 0 if the object does not connect to any database file.

fwmkeys(prefix, max)

Get forward matching keys.
`prefix' specifies the prefix of the corresponding keys.
`max' specifies the maximum number of keys to be fetched. If it is not defined or negative, no limit is specified.
The return value is a list object of the keys of the corresponding records. This method does never fail. It returns an empty list even if no record corresponds.

get(key)

Retrieve a record.
`key' specifies the key.
If successful, the return value is the value of the corresponding record. `nil' is returned if no record corresponds.
If the key of duplicated records is specified, the value of the first one is selected.

getlist(key)

Retrieve records.
`key' specifies the key.
If successful, the return value is a list object of the values of the corresponding records. `nil' is returned if no record corresponds.

open(path, omode)

Open a database file.
`path' specifies the path of the database file.
`omode' specifies the connection mode: `TokyoCabinet::BDB::OWRITER' as a writer, `TokyoCabinet::BDB::OREADER' as a reader. If the mode is `TokyoCabinet::BDB::OWRITER', the following may be added by bitwise-or: `TokyoCabinet::BDB::OCREAT', which means it creates a new database if not exist, `TokyoCabinet::BDB::OTRUNC', which means it creates a new database regardless if one exists, `TokyoCabinet::BDB::OTSYNC', which means every transaction synchronizes updated contents with the device. Both of `TokyoCabinet::BDB::OREADER' and `TokyoCabinet::BDB::OWRITER' can be added to by bitwise-or: `TokyoCabinet::BDB::ONOLCK', which means it opens the database file without file locking, or `TokyoCabinet::BDB::OLCKNB', which means locking is performed without blocking. If it is not defined, `TokyoCabinet::BDB::OREADER' is specified.
If successful, the return value is true, else, it is false.

optimize(lmemb, nmemb, bnum, apow, fpow, opts)

Optimize the database file.
`lmemb' specifies the number of members in each leaf page. If it is not defined or not more than 0, the default value is specified. The default value is 128.
`nmemb' specifies the number of members in each non-leaf page. If it is not defined or not more than 0, the default value is specified. The default value is 256.
`bnum' specifies the number of elements of the bucket array. If it is not defined or not more than 0, the default value is specified. The default value is two times of the number of pages.
`apow' specifies the size of record alignment by power of 2. If it is not defined or negative, the current setting is not changed.
`fpow' specifies the maximum number of elements of the free block pool by power of 2. If it is not defined or negative, the current setting is not changed.
`opts' specifies options by bitwise-or: `TokyoCabinet::BDB::TLARGE' specifies that the size of the database can be larger than 2GB by using 64-bit bucket array, `TokyoCabinet::BDB::TDEFLATE' specifies that each record is compressed with Deflate encoding, `TokyoCabinet::BDB::TBZIP' specifies that each record is compressed with BZIP2 encoding, `TokyoCabinet::BDB::TTCBS' specifies that each record is compressed with TCBS encoding. If it is not defined or 0xff, the current setting is not changed.
If successful, the return value is true, else, it is false.
This method is useful to reduce the size of the database file with data fragmentation by successive updating.

out(key)

Remove a record.
`key' specifies the key.
If successful, the return value is true, else, it is false.
If the key of duplicated records is specified, the value of the first one is selected.

outlist(key)

Remove records.
`key' specifies the key.
If successful, the return value is true, else, it is false.
If the key of duplicated records is specified, all of them are removed.

path()

Get the path of the database file.
The return value is the path of the database file or `nil' if the object does not connect to any database file.

put(key, value)

Store a record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, it is overwritten.

putcat(key, value)

Concatenate a value at the end of the existing record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If there is no corresponding record, a new record is created.

putdup(key, value)

Store a record with allowing duplication of keys.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, the new record is placed after the existing one.

putkeep(key, value)

Store a new record.
`key' specifies the key.
`value' specifies the value.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, this method has no effect.

putlist(key, values)

Store records with allowing duplication of keys.
`key' specifies the key.
`values' specifies an array of the values.
If successful, the return value is true, else, it is false.
If a record with the same key exists in the database, the new records are placed after the existing one.

range(bkey, binc, ekey, einc, max)

Get keys of ranged records.
`bkey' specifies the key of the beginning border. If it is not defined, the first record is specified.
`binc' specifies whether the beginning border is inclusive or not. If it is not defined, false is specified.
`ekey' specifies the key of the ending border. If it is not defined, the last record is specified.
`einc' specifies whether the ending border is inclusive or not. If it is not defined, false is specified.
`max' specifies the maximum number of keys to be fetched. If it is not defined or negative, no limit is specified.
The return value is a list object of the keys of the corresponding records. This method does never fail. It returns an empty list even if no record corresponds.

rnum()

Get the number of records.
The return value is the number of records or 0 if the object does not connect to any database file.

setcache(lcnum, ncnum)

Set the caching parameters.
`lcnum' specifies the maximum number of leaf nodes to be cached. If it is not defined or not more than 0, the default value is specified. The default value is 1024.
`ncnum' specifies the maximum number of non-leaf nodes to be cached. If it is not defined or not more than 0, the default value is specified. The default value is 512.
If successful, the return value is true, else, it is false.
Note that the tuning parameters of the database should be set before the database is opened.

setcmpfunc(cmp)

Set the custom comparison function.
`cmp' specifies the custom comparison function. It should be an instance of the class `Proc'.
If successful, the return value is true, else, it is false.
The default comparison function compares keys of two records by lexical order. The constants `TokyoCabinet::BDB::CMPLEXICAL' (dafault), `TokyoCabinet::BDB::CMPDECIMAL', `TokyoCabinet::BDB::CMPINT32', and `TokyoCabinet::BDB::CMPINT64' are built-in. Note that the comparison function should be set before the database is opened. Moreover, user-defined comparison functions should be set every time the database is being opened.

setdfunit(dfunit)

Set the unit step number of auto defragmentation.
`dfunit' specifie the unit step number. If it is not more than 0, the auto defragmentation is disabled. It is disabled by default.
If successful, the return value is true, else, it is false.
Note that the defragmentation parameters should be set before the database is opened.

setxmsiz(xmsiz)

Set the size of the extra mapped memory.
`xmsiz' specifies the size of the extra mapped memory. If it is not defined or not more than 0, the extra mapped memory is disabled. It is disabled by default.
If successful, the return value is true, else, it is false.
Note that the mapping parameters should be set before the database is opened.

sync()

Synchronize updated contents with the file and the device.
If successful, the return value is true, else, it is false.
This method is useful when another process connects the same database file.

tranabort()

Abort the transaction.
If successful, the return value is true, else, it is false.
Update in the transaction is discarded when it is aborted. The state of the database is rollbacked to before transaction.

tranbegin()

Begin the transaction.
If successful, the return value is true, else, it is false.
The database is locked by the thread while the transaction so that only one transaction can be activated with a database object at the same time. Thus, the serializable isolation level is assumed if every database operation is performed in the transaction. Because all pages are cached on memory while the transaction, the amount of referred records is limited by the memory capacity. If the database is closed during transaction, the transaction is aborted implicitly.

trancommit()

Commit the transaction.
If successful, the return value is true, else, it is false.
Update in the transaction is fixed when it is committed successfully.

tune(lmemb, nmemb, bnum, apow, fpow, opts)

Set the tuning parameters.
`lmemb' specifies the number of members in each leaf page. If it is not defined or not more than 0, the default value is specified. The default value is 128.
`nmemb' specifies the number of members in each non-leaf page. If it is not defined or not more than 0, the default value is specified. The default value is 256.
`bnum' specifies the number of elements of the bucket array. If it is not defined or not more than 0, the default value is specified. The default value is 32749. Suggested size of the bucket array is about from 1 to 4 times of the number of all pages to be stored.
`apow' specifies the size of record alignment by power of 2. If it is not defined or negative, the default value is specified. The default value is 4 standing for 2^8=256.
`fpow' specifies the maximum number of elements of the free block pool by power of 2. If it is not defined or negative, the default value is specified. The default value is 10 standing for 2^10=1024.
`opts' specifies options by bitwise-or: `TokyoCabinet::BDB::TLARGE' specifies that the size of the database can be larger than 2GB by using 64-bit bucket array, `TokyoCabinet::BDB::TDEFLATE' specifies that each record is compressed with Deflate encoding, `TokyoCabinet::BDB::TBZIP' specifies that each record is compressed with BZIP2 encoding, `TokyoCabinet::BDB::TTCBS' specifies that each record is compressed with TCBS encoding. If it is not defined, no option is specified.
If successful, the return value is true, else, it is false. Note that the tuning parameters of the database should be set before the database is opened.

vanish()

Remove all records.
If successful, the return value is true, else, it is false.

vnum(key)

Get the number of records corresponding a key.
`key' specifies the key.
If successful, the return value is the number of the corresponding records, else, it is 0.

vsiz(key)

Get the size of the value of a record.
`key' specifies the key.
If successful, the return value is the size of the value of the corresponding record, else, it is -1.
If the key of duplicated records is specified, the value of the first one is selected.