NAME
Curia - the extended API of QDBM
SYNOPSIS
#include <depot.h>
#include <curia.h>
#include <stdlib.h>
CURIA *cropen(const char *name, int omode, int bnum, int dnum);
int crclose(CURIA *curia);
int crput(CURIA *curia, const char *kbuf, int ksiz, const char *vbuf,
int vsiz, int dmode);
int crout(CURIA *curia, const char *kbuf, int ksiz);
char *crget(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, int *sp);
int crgetwb(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, char *vbuf);
int crvsiz(CURIA *curia, const char *kbuf, int ksiz);
int criterinit(CURIA *curia);
char *criternext(CURIA *curia, int *sp);
int crsetalign(CURIA *curia, int align);
int crsetfbpsiz(CURIA *curia, int size);
int crsync(CURIA *curia);
int croptimize(CURIA *curia, int bnum);
char *crname(CURIA *curia);
int crfsiz(CURIA *curia);
double crfsizd(CURIA *curia);
int crbnum(CURIA *curia);
int crbusenum(CURIA *curia);
int crrnum(CURIA *curia);
int crwritable(CURIA *curia);
int crfatalerror(CURIA *curia);
int crinode(CURIA *curia);
time_t crmtime(CURIA *curia);
int crremove(const char *name);
int crrepair(const char *name);
int crexportdb(CURIA *curia, const char *name);
int crimportdb(CURIA *curia, const char *name);
char *crsnaffle(const char *name, const char *kbuf, int ksiz, int *sp);
int crputlob(CURIA *curia, const char *kbuf, int ksiz, const char
*vbuf, int vsiz, int dmode);
int croutlob(CURIA *curia, const char *kbuf, int ksiz);
char *crgetlob(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, int *sp);
int crgetlobfd(CURIA *curia, const char *kbuf, int ksiz);
int crvsizlob(CURIA *curia, const char *kbuf, int ksiz);
int crrnumlob(CURIA *curia);
DESCRIPTION
Curia is the extended API of QDBM. It provides routines for managing
multiple database files in a directory. Restrictions of some file
systems that the size of each file is limited are escaped by dividing a
database file into two or more. If the database files deploy on
multiple devices, the scalability is improved.
Although Depot creates a database with a file name, Curia creates a
database with a directory name. A database file named as ‘depot’ is
placed in the specified directory. Although it keeps the attribute of
the database, it does not keep the entities of the records. Besides,
sub directories are created by the number of division of the database,
named with 4 digits. The database files are placed in the
subdirectories. The entities of the records are stored in the database
file. For example, in the case that a database directory named as
‘casket’ and the number of division is 3, ‘casket/depot’,
‘casket/0001/depot’, ‘casket/0002/depot’ and ‘casket/0003/depot’ are
created. No error occurs even if the namesake directory exists when
creating a database. So, if sub directories exists and some devices
are mounted on the sub directories, the database files deploy on the
multiple devices. It is possible for the database files to deploy on
multiple file servers using NFS and so on.
Curia features managing large objects. Although usual records are
stored in some database files, records of large objects are stored in
individual files. Because the files of large objects are deployed in
different directories named with the hash values, the access speed is
part-way robust although it is slower than the speed of usual records.
Large and not often accessed data should be secluded as large objects.
By doing this, the access speed of usual records is improved. The
directory hierarchies of large objects are placed in the directory
named as ‘lob’ in the sub directories of the database. Because the key
spaces of the usual records and the large objects are different, the
operations keep out of each other.
In order to use Curia, you should include ‘depot.h’, ‘curia.h’ and
‘stdlib.h’ in the source files. Usually, the following description
will be near the beginning of a source file.
#include <depot.h>
#include <curia.h>
#include <stdlib.h>
A pointer to ‘CURIA’ is used as a database handle. It is like that
some file I/O routines of ‘stdio.h’ use a pointer to ‘FILE’. A
database handle is opened with the function ‘cropen’ and closed with
‘crclose’. You should not refer directly to any member of the handle.
If a fatal error occurs in a database, any access method via the handle
except ‘crclose’ will not work and return error status. Although a
process is allowed to use multiple database handles at the same time,
handles of the same database directory should not be used.
Curia also assign the external variable ‘dpecode’ with the error code.
The function ‘dperrmsg’ is used in order to get the message of the
error code.
The function ‘cropen’ is used in order to get a database handle.
CURIA *cropen(const char *name, int omode, int bnum, int dnum);
‘name’ specifies the name of a database directory. ‘omode’
specifies the connection mode: ‘CR_OWRITER’ as a writer,
‘CR_OREADER’ as a reader. If the mode is ‘CR_OWRITER’, the
following may be added by bitwise or: ‘CR_OCREAT’, which means
it creates a new database if not exist, ‘CR_OTRUNC’, which means
it creates a new database regardless if one exists. Both of
‘CR_OREADER’ and ‘CR_OWRITER’ can be added to by bitwise or:
‘CR_ONOLCK’, which means it opens a database directory without
file locking, or ‘CR_OLCKNB’, which means locking is performed
without blocking. ‘CR_OCREAT’ can be added to by bitwise or:
‘CR_OSPARSE’, which means it creates database files as sparse
files. ‘bnum’ specifies the number of elements of each bucket
array. If it is not more than 0, the default value is
specified. The size of each bucket array is determined on
creating, and can not be changed except for by optimization of
the database. Suggested size of each bucket array is about from
0.5 to 4 times of the number of all records to store. ‘dnum’
specifies the number of division of the database. If it is not
more than 0, the default value is specified. The number of
division can not be changed from the initial value. The max
number of division is 512. The return value is the database
handle or ‘NULL’ if it is not successful. While connecting as a
writer, an exclusive lock is invoked to the database directory.
While connecting as a reader, a shared lock is invoked to the
database directory. The thread blocks until the lock is
achieved. If ‘CR_ONOLCK’ is used, the application is
responsible for exclusion control.
The function ‘crclose’ is used in order to close a database handle.
int crclose(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is true, else, it is false. Because the region of a
closed handle is released, it becomes impossible to use the
handle. Updating a database is assured to be written when the
handle is closed. If a writer opens a database but does not
close it appropriately, the database will be broken.
The function ‘crput’ is used in order to store a record.
int crput(CURIA *curia, const char *kbuf, int ksiz, const char *vbuf,
int vsiz, int dmode);
‘curia’ specifies a database handle connected as a writer.
‘kbuf’ specifies the pointer to the region of a key. ‘ksiz’
specifies the size of the region of the key. If it is negative,
the size is assigned with ‘strlen(kbuf)’. ‘vbuf’ specifies the
pointer to the region of a value. ‘vsiz’ specifies the size of
the region of the value. If it is negative, the size is
assigned with ‘strlen(vbuf)’. ‘dmode’ specifies behavior when
the key overlaps, by the following values: ‘CR_DOVER’, which
means the specified value overwrites the existing one,
‘CR_DKEEP’, which means the existing value is kept, ‘CR_DCAT’,
which means the specified value is concatenated at the end of
the existing value. If successful, the return value is true,
else, it is false.
The function ‘crout’ is used in order to delete a record.
int crout(CURIA *curia, const char *kbuf, int ksiz);
‘curia’ specifies a database handle connected as a writer.
‘kbuf’ specifies the pointer to the region of a key. ‘ksiz’
specifies the size of the region of the key. If it is negative,
the size is assigned with ‘strlen(kbuf)’. If successful, the
return value is true, else, it is false. false is returned when
no record corresponds to the specified key.
The function ‘crget’ is used in order to retrieve a record.
char *crget(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, int *sp);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. ‘start’ specifies the offset address of
the beginning of the region of the value to be read. ‘max’
specifies the max size to be read. If it is negative, the size
to read is unlimited. ‘sp’ specifies the pointer to a variable
to which the size of the region of the return value is assigned.
If it is ‘NULL’, it is not used. If successful, the return
value is the pointer to the region of the value of the
corresponding record, else, it is ‘NULL’. ‘NULL’ is returned
when no record corresponds to the specified key or the size of
the value of the corresponding record is less than ‘start’.
Because an additional zero code is appended at the end of the
region of the return value, the return value can be treated as a
character string. Because the region of the return value is
allocated with the ‘malloc’ call, it should be released with the
‘free’ call if it is no longer in use.
The function ‘crgetwb’ is used in order to retrieve a record and write
the value into a buffer.
int crgetwb(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, char *vbuf);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. ‘start’ specifies the offset address of
the beginning of the region of the value to be read. ‘max’
specifies the max size to be read. It shuld be equal to or less
than the size of the writing buffer. ‘vbuf’ specifies the
pointer to a buffer into which the value of the corresponding
record is written. If successful, the return value is the size
of the written data, else, it is -1. -1 is returned when no
record corresponds to the specified key or the size of the value
of the corresponding record is less than ‘start’. Note that no
additional zero code is appended at the end of the region of the
writing buffer.
The function ‘crvsiz’ is used in order to get the size of the value of
a record.
int crvsiz(CURIA *curia, const char *kbuf, int ksiz);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. If successful, the return value is the
size of the value of the corresponding record, else, it is -1.
Because this function does not read the entity of a record, it
is faster than ‘crget’.
The function ‘criterinit’ is used in order to initialize the iterator
of a database handle.
int criterinit(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is true, else, it is false. The iterator is used in order
to access the key of every record stored in a database.
The function ‘criternext’ is used in order to get the next key of the
iterator.
char *criternext(CURIA *curia, int *sp);
‘curia’ specifies a database handle. ‘sp’ specifies the pointer
to a variable to which the size of the region of the return
value is assigned. If it is ‘NULL’, it is not used. If
successful, the return value is the pointer to the region of the
next key, else, it is ‘NULL’. ‘NULL’ is returned when no record
is to be get out of the iterator. Because an additional zero
code is appended at the end of the region of the return value,
the return value can be treated as a character string. Because
the region of the return value is allocated with the ‘malloc’
call, it should be released with the ‘free’ call if it is no
longer in use. It is possible to access every record by
iteration of calling this function. However, it is not assured
if updating the database is occurred while the iteration.
Besides, the order of this traversal access method is arbitrary,
so it is not assured that the order of storing matches the one
of the traversal access.
The function ‘crsetalign’ is used in order to set alignment of a
database handle.
int crsetalign(CURIA *curia, int align);
‘curia’ specifies a database handle connected as a writer.
‘align’ specifies the size of alignment. If successful, the
return value is true, else, it is false. If alignment is set to
a database, the efficiency of overwriting values is improved.
The size of alignment is suggested to be average size of the
values of the records to be stored. If alignment is positive,
padding whose size is multiple number of the alignment is
placed. If alignment is negative, as ‘vsiz’ is the size of a
value, the size of padding is calculated with ‘(vsiz / pow(2,
abs(align) - 1))’. Because alignment setting is not saved in a
database, you should specify alignment every opening a database.
The function ‘crsetfbpsiz’ is used in order to set the size of the free
block pool of a database handle.
int crsetfbpsiz(CURIA *curia, int size);
‘curia’ specifies a database handle connected as a writer.
‘size’ specifies the size of the free block pool of a database.
If successful, the return value is true, else, it is false. The
default size of the free block pool is 16. If the size is
greater, the space efficiency of overwriting values is improved
with the time efficiency sacrificed.
The function ‘crsync’ is used in order to synchronize updating contents
with the files and the devices.
int crsync(CURIA *curia);
‘curia’ specifies a database handle connected as a writer. If
successful, the return value is true, else, it is false. This
function is useful when another process uses the connected
database directory.
The function ‘croptimize’ is used in order to optimize a database.
int croptimize(CURIA *curia, int bnum);
‘curia’ specifies a database handle connected as a writer.
‘bnum’ specifies the number of the elements of each bucket
array. If it is not more than 0, the default value is
specified. In an alternating succession of deleting and storing
with overwrite or concatenate, dispensable regions accumulate.
This function is useful to do away with them.
The function ‘crname’ is used in order to get the name of a database.
char *crname(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the pointer to the region of the name of the database,
else, it is ‘NULL’. Because the region of the return value is
allocated with the ‘malloc’ call, it should be released with the
‘free’ call if it is no longer in use.
The function ‘crfsiz’ is used in order to get the total size of
database files.
int crfsiz(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the total size of the database files, else, it is -1.
If the total size is more than 2GB, the return value overflows.
The function ‘crfsizd’ is used in order to get the total size of
database files as double-precision floating-point number.
double crfsizd(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the total size of the database files, else, it is -1.0.
The function ‘crbnum’ is used in order to get the total number of the
elements of each bucket array.
int crbnum(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the total number of the elements of each bucket array,
else, it is -1.
The function ‘crbusenum’ is used in order to get the total number of
the used elements of each bucket array.
int crbusenum(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the total number of the used elements of each bucket
array, else, it is -1. This function is inefficient because it
accesses all elements of each bucket array.
The function ‘crrnum’ is used in order to get the number of the records
stored in a database.
int crrnum(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the number of the records stored in the database, else,
it is -1.
The function ‘crwritable’ is used in order to check whether a database
handle is a writer or not.
int crwritable(CURIA *curia);
‘curia’ specifies a database handle. The return value is true
if the handle is a writer, false if not.
The function ‘crfatalerror’ is used in order to check whether a
database has a fatal error or not.
int crfatalerror(CURIA *curia);
‘curia’ specifies a database handle. The return value is true
if the database has a fatal error, false if not.
The function ‘crinode’ is used in order to get the inode number of a
database directory.
int crinode(CURIA *curia);
‘curia’ specifies a database handle. The return value is the
inode number of the database directory.
The function ‘crmtime’ is used in order to get the last modified time
of a database.
time_t crmtime(CURIA *curia);
‘curia’ specifies a database handle. The return value is the
last modified time of the database.
The function ‘crremove’ is used in order to remove a database
directory.
int crremove(const char *name);
‘name’ specifies the name of a database directory. If
successful, the return value is true, else, it is false.
The function ‘crrepair’ is used in order to repair a broken database
directory.
int crrepair(const char *name);
‘name’ specifies the name of a database directory. If
successful, the return value is true, else, it is false. There
is no guarantee that all records in a repaired database
directory correspond to the original or expected state.
The function ‘crexportdb’ is used in order to dump all records as
endian independent data.
int crexportdb(CURIA *curia, const char *name);
‘curia’ specifies a database handle. ‘name’ specifies the name
of an output directory. If successful, the return value is
true, else, it is false. Note that large objects are ignored.
The function ‘crimportdb’ is used in order to load all records from
endian independent data.
int crimportdb(CURIA *curia, const char *name);
‘curia’ specifies a database handle connected as a writer. The
database of the handle must be empty. ‘name’ specifies the name
of an input directory. If successful, the return value is true,
else, it is false. Note that large objects are ignored.
The function ‘crsnaffle’ is used in order to retrieve a record directly
from a database directory.
char *crsnaffle(const char *name, const char *kbuf, int ksiz, int *sp);
‘name’ specifies the name of a database directory. ‘kbuf’
specifies the pointer to the region of a key. ‘ksiz’ specifies
the size of the region of the key. If it is negative, the size
is assigned with ‘strlen(kbuf)’. ‘sp’ specifies the pointer to
a variable to which the size of the region of the return value
is assigned. If it is ‘NULL’, it is not used. If successful,
the return value is the pointer to the region of the value of
the corresponding record, else, it is ‘NULL’. ‘NULL’ is
returned when no record corresponds to the specified key.
Because an additional zero code is appended at the end of the
region of the return value, the return value can be treated as a
character string. Because the region of the return value is
allocated with the ‘malloc’ call, it should be released with the
‘free’ call if it is no longer in use. Although this function
can be used even while the database directory is locked by
another process, it is not assured that recent updated is
reflected.
The function ‘crputlob’ is used in order to store a large object.
int crputlob(CURIA *curia, const char *kbuf, int ksiz, const char
*vbuf, int vsiz, int dmode);
‘curia’ specifies a database handle connected as a writer.
‘kbuf’ specifies the pointer to the region of a key. ‘ksiz’
specifies the size of the region of the key. If it is negative,
the size is assigned with ‘strlen(kbuf)’. ‘vbuf’ specifies the
pointer to the region of a value. ‘vsiz’ specifies the size of
the region of the value. If it is negative, the size is
assigned with ‘strlen(vbuf)’. ‘dmode’ specifies behavior when
the key overlaps, by the following values: ‘CR_DOVER’, which
means the specified value overwrites the existing one,
‘CR_DKEEP’, which means the existing value is kept, ‘CR_DCAT’,
which means the specified value is concatenated at the end of
the existing value. If successful, the return value is true,
else, it is false.
The function ‘croutlob’ is used in order to delete a large object.
int croutlob(CURIA *curia, const char *kbuf, int ksiz);
‘curia’ specifies a database handle connected as a writer.
‘kbuf’ specifies the pointer to the region of a key. ‘ksiz’
specifies the size of the region of the key. If it is negative,
the size is assigned with ‘strlen(kbuf)’. If successful, the
return value is true, else, it is false. false is returned when
no large object corresponds to the specified key.
The function ‘crgetlob’ is used in order to retrieve a large object.
char *crgetlob(CURIA *curia, const char *kbuf, int ksiz, int start, int
max, int *sp);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. ‘start’ specifies the offset address of
the beginning of the region of the value to be read. ‘max’
specifies the max size to be read. If it is negative, the size
to read is unlimited. ‘sp’ specifies the pointer to a variable
to which the size of the region of the return value is assigned.
If it is ‘NULL’, it is not used. If successful, the return
value is the pointer to the region of the value of the
corresponding large object, else, it is ‘NULL’. ‘NULL’ is
returned when no large object corresponds to the specified key
or the size of the value of the corresponding large object is
less than ‘start’. Because an additional zero code is appended
at the end of the region of the return value, the return value
can be treated as a character string. Because the region of the
return value is allocated with the ‘malloc’ call, it should be
released with the ‘free’ call if it is no longer in use.
The function ‘crgetlobfd’ is used in order to get the file descriptor
of a large object.
int crgetlobfd(CURIA *curia, const char *kbuf, int ksiz);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. If successful, the return value is the
file descriptor of the corresponding large object, else, it is
-1. -1 is returned when no large object corresponds to the
specified key. The returned file descriptor is opened with the
‘open’ call. If the database handle was opened as a writer, the
descriptor is writable (O_RDWR), else, it is not writable
(O_RDONLY). The descriptor should be closed with the ‘close’
call if it is no longer in use.
The function ‘crvsizlob’ is used in order to get the size of the value
of a large object.
int crvsizlob(CURIA *curia, const char *kbuf, int ksiz);
‘curia’ specifies a database handle. ‘kbuf’ specifies the
pointer to the region of a key. ‘ksiz’ specifies the size of
the region of the key. If it is negative, the size is assigned
with ‘strlen(kbuf)’. If successful, the return value is the
size of the value of the corresponding large object, else, it is
-1. Because this function does not read the entity of a large
object, it is faster than ‘crgetlob’.
The function ‘crrnumlob’ is used in order to get the number of the
large objects stored in a database.
int crrnumlob(CURIA *curia);
‘curia’ specifies a database handle. If successful, the return
value is the number of the large objects stored in the database,
else, it is -1.
If QDBM was built with POSIX thread enabled, the global variable
‘dpecode’ is treated as thread specific data, and functions of Curia
are reentrant. In that case, they are thread-safe as long as a handle
is not accessed by threads at the same time, on the assumption that
‘errno’, ‘malloc’, and so on are thread-safe.
SEE ALSO
qdbm(3), depot(3), relic(3), hovel(3), cabin(3), villa(3), odeum(3),
ndbm(3), gdbm(3)