QDBM(3)

NAME
Villa - the advanced API of QDBM

SYNOPSIS

#include <depot.h>
#include <cabin.h>
#include <villa.h>
#include <stdlib.h>

typedef int(*VLCFUNC)(const char *aptr, int asiz, const char *bptr, int bsiz);
VILLA *vlopen(const char *name, int omode, VLCFUNC cmp);
int vlclose(VILLA *villa);
int vlput(VILLA *villa, const char *kbuf, int ksiz, const char *vbuf, int vsiz, int dmode);
int vlout(VILLA *villa, const char *kbuf, int ksiz);
char *vlget(VILLA *villa, const char *kbuf, int ksiz, int *sp);
int vlvnum(VILLA *villa, const char *kbuf, int ksiz);
int vlputlist(VILLA *villa, const char *kbuf, int ksiz, CBLIST *vals);
int vloutlist(VILLA *villa, const char *kbuf, int ksiz);
CBLIST *vlgetlist(VILLA *villa, const char *kbuf, int ksiz);
int vlcurfirst(VILLA *villa);
int vlcurlast(VILLA *villa);
int vlcurprev(VILLA *villa);
int vlcurnext(VILLA *villa);
int vlcurjump(VILLA *villa, const char *kbuf, int ksiz, int jmode);
char *vlcurkey(VILLA *villa, int *sp);
char *vlcurval(VILLA *villa, int *sp);
void vlsettuning(VILLA *villa, int lrecmax, int nidxmax, int lcnum, int ncnum);
int vlsync(VILLA *villa);
int vloptimize(VILLA *villa);
char *vlname(VILLA *villa);
int vlfsiz(VILLA *villa);
int vllnum(VILLA *villa);
int vlnnum(VILLA *villa);
int vlrnum(VILLA *villa);
int vlwritable(VILLA *villa);
int vlfatalerror(VILLA *villa);
int vlinode(VILLA *villa);
int vltranbegin(VILLA *villa);
int vltrancommit(VILLA *villa);
int vltranabort(VILLA *villa);
int vlremove(const char *name);
int vleconv(const char *name, int big);

DESCRIPTION

Villa is the advanced API of QDBM. It provides routines for managing a database file of B+ tree. Each record is stored being sorted in order defined by a user. As for hash databases, retrieving method is provided only as complete accord. However, with Villa, it is possible to retrieve records specified by range. Cursor is used in order to access each record in order. It is possible to store records duplicating keys in a database. Moreover, according to the transaction mechanism, you can commit or abort operations of a database in a lump.

Villa is implemented, based on Depot and Cabin. A database file of Villa is actual one of Depot. Although processing speed of retrieving and storing is slower than Depot, the size of a database is smaller.

In order to use Villa, you should include `depot.h', `cabin.h', `villa.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 <cabin.h>
    #include <villa.h>
    #include <stdlib.h>

A pointer to `VILLA' 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 `vlopen' and closed with `vlclose'. 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 `vlclose' 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 file should not be used. Before the cursor is used, it should be initialized by one of `vlcurfirst', `vlcurlast' or `vlcurjump'. Also after storing or deleting a record, the cursor should be initialized.

Villa 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.

You can define a comparing function to specify the order of records. The function should be the following type.

typedef int(*VLCFUNC)(const char *aptr, int asiz, const char *bptr, int bsiz);
    `aptr' specifies the pointer to the region of one key. `asiz' specifies the size of the region of one key. `bptr' specifies the pointer to the region of the other key. `bsiz' specifies the size of the region of the other key. The return value is positive if the former is big, negative if the latter is big, 0 if both are equivalent.

The function `vlopen' is used in order to get a database handle.

VILLA *vlopen(const char *name, int omode, VLCFUNC cmp);
    `name' specifies the name of a database file. `omode' specifies the connection mode: `VL_OWRITER' as a writer, `VL_OREADER' as a reader. If the mode is `VL_OWRITER', the following may be added by bitwise or: `VL_OCREAT', which means it creates a new database if not exist, `VL_OTRUNC', which means it creates a new database regardless if one exists. Both of `VL_OREADER' and `VL_OWRITER' can be added to by bitwise or: `VL_ONOLCK', which means it opens a database file without file locking. `cmp' specifies the comparing function: `VL_CMPLEX' comparing keys in lexical order, `VL_CMPINT' comparing keys as objects of `int' in native byte order, `VL_CMPNUM' comparing keys as numbers of big endian, `VL_CMPDEC' comparing keys as decimal strings. Any function based on the declaration of the type `VLCFUNC' can be assigned to the comparing function. The comparing function should be kept same in the life of a database. 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 file. While connecting as a reader, a shared lock is invoked to the database file. The thread blocks until the lock is achieved. If `VL_ONOLCK' is used, the application is responsible for exclusion control.

The function `vlclose' is used in order to close a database handle.

int vlclose(VILLA *villa);
    `villa' 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. If the transaction is activated and not committed, it is aborted.

The function `vlput' is used in order to store a record.

int vlput(VILLA *villa, const char *kbuf, int ksiz, const char *vbuf, int vsiz, int dmode);
    `villa' 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: `VL_DOVER', which means the specified value overwrites the existing one, `VL_DKEEP', which means the existing value is kept, `VL_DDUP', which means duplication of keys is allowed. If successful, the return value is true, else, it is false. A duplicated record is stored at the tail of the records of the same key. The cursor becomes unavailable due to updating database.

The function `vlout' is used in order to delete a record.

int vlout(VILLA *villa, const char *kbuf, int ksiz);
    `villa' 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. When the key of duplicated records is specified, the first record of the same key is deleted. The cursor becomes unavailable due to updating database.

The function `vlget' is used in order to retrieve a record.

char *vlget(VILLA *villa, const char *kbuf, int ksiz, int *sp);
    `villa' 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)'. `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. When the key of duplicated records is specified, the value of the first record of the same key is selected. 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 `vlvnum' is used in order to get the number of records corresponding a key.

int vlvnum(VILLA *villa, const char *kbuf, int ksiz);
    `villa' 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)'. The return value is the number of corresponding records. If no record corresponds, 0 is returned.

The function `vlputlist' is used in order to store plural records corresponding a key.

int vlputlist(VILLA *villa, const char *kbuf, int ksiz, CBLIST *vals);
    `villa' 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)'. `vals' specifies a list handle of values. The list should not be empty. If successful, the return value is true, else, it is false. The cursor becomes unavailable due to updating database.

The function `vloutlist' is used in order to delete all records corresponding a key.

int vloutlist(VILLA *villa, const char *kbuf, int ksiz);
    `villa' 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 cursor becomes unavailable due to updating database.

The function `vlgetlist' is used in order to retrieve values of all records corresponding a key.

CBLIST *vlgetlist(VILLA *villa, const char *kbuf, int ksiz);
    `villa' 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 a list handle of the values of the corresponding records, else, it is `NULL'. `NULL' is returned when no record corresponds to the specified key.

The function `vlcurfirst' is used in order to move the cursor to the first record.

int vlcurfirst(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is true, else, it is false. False is returned if there is no record in the database.

The function `vlcurlast' is used in order to move the cursor to the last record.

int vlcurlast(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is true, else, it is false. False is returned if there is no record in the database.

The function `vlcurprev' is used in order to move the cursor to the previous record.

int vlcurprev(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is true, else, it is false. False is returned if there is no previous record.

The function `vlcurnext' is used in order to move the cursor to the next record.

int vlcurnext(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is true, else, it is false. False is returned if there is no next record.

The function `vlcurjump' is used in order to move the cursor to positon around a record.

int vlcurjump(VILLA *villa, const char *kbuf, int ksiz, int jmode);
    `villa' 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)'. `jmode' specifies detail adjustment: `VL_JFORWARD', which means that the cursor is set to the first record of the same key and that the cursor is set to the next substitute if completely matching record does not exist, `VL_JBACKWARD', which means that the cursor is set to the last record of the same key and that the cursor is set to the previous substitute if completely matching record does not exist. If successful, the return value is true, else, it is false. False is returned if there is no record corresponding the condition.

The function `vlcurkey' is used in order to get the key of the record where the cursor is.

char *vlcurkey(VILLA *villa, int *sp);
    `villa' 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 key of the corresponding record, else, it is `NULL'. `NULL' is returned when no record corresponds to the cursor. 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 `vlcurval' is used in order to get the value of the record where the cursor is.

char *vlcurval(VILLA *villa, int *sp);
    `villa' specifies a database handle. `sp' specifies the pointer to a variable to which the size of the region of the return value 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 cursor. 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 `vlsettuning' is used in order to set the tuning parameters for performance.

void vlsettuning(VILLA *villa, int lrecmax, int nidxmax, int lcnum, int ncnum);
    `villa' specifies a database handle. `lrecmax' specifies the max number of records in a leaf node of B+ tree. If it is not more than 0, the default value is specified. `nidxmax' specifies the max number of indexes in a non-leaf node of B+ tree. If it is not more than 0, the default value is specified. `lcnum' specifies the max number of caching leaf nodes. If it is not more than 0, the default value is specified. `ncnum' specifies the max number of caching non-leaf nodes. If it is not more than 0, the default value is specified. The default setting is equivalent to `vlsettuning(49, 192, 1024, 512)'. Because tuning paremeters are not saved in a database, you should specify them every opening a database.

The function `vlsync' is used in order to synchronize updating contents with the file and the device.

int vlsync(VILLA *villa);
    `villa' 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 file. This function shuold not be used while the transaction is activated.

The function `vloptimize' is used in order to optimize a database.

int vloptimize(VILLA *villa);
    `villa' specifies a database handle connected as a writer. If successful, the return value is true, else, it is false. In an alternating succession of deleting and storing with overwrite or concatenate, dispensable regions accumulate. This function is useful to do away with them. This function shuold not be used while the transaction is activated.

The function `vlname' is used in order to get the name of a database.

char *vlname(VILLA *villa);
    `villa' 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 `vlfsiz' is used in order to get the size of a database file.

int vlfsiz(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is the size of the database file, else, it is -1. Because of the I/O buffer, the return value may be less than the real size.

The function `vllnum' is used in order to get the number of the leaf nodes of B+ tree.

int vllnum(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is the number of the leaf nodes, else, it is -1.

The function `vlnnum' is used in order to get the number of the non-leaf nodes of B+ tree.

int vlnnum(VILLA *villa);
    `villa' specifies a database handle. If successful, the return value is the number of the non-leaf nodes, else, it is -1.

The function `vlrnum' is used in order to get the number of the records stored in a database.

int vlrnum(VILLA *villa);
    `villa' 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 `vlwritable' is used in order to check whether a database handle is a writer or not.

int vlwritable(VILLA *villa);
    `villa' specifies a database handle. The return value is true if the handle is a writer, false if not.

The function `vlfatalerror' is used in order to check whether a database has a fatal error or not.

int vlfatalerror(VILLA *villa);
    `villa' specifies a database handle. The return value is true if the database has a fatal error, false if not.

The function `vlinode' is used in order to get the inode number of a database file.

int vlinode(VILLA *villa);
    `villa' specifies a database handle. The return value is the inode number of the database file.

The function `vltranbegin' is used in order to begin the transaction.

int vltranbegin(VILLA *villa);
    `villa' specifies a database handle connected as a writer. If successful, the return value is true, else, it is false. Because this function does not perform mutual excrusion control in multi-thread, the application is responsible for it. Only one transaction can be activated with a database handle at the same time.

The function `vltrancommit' is used in order to commit the transaction.

int vltrancommit(VILLA *villa);
    `villa' specifies a database handle connected as a writer. If successful, the return value is true, else, it is false. Updating a database in the transaction is fixed when it is committed successfully.

The function `vltranabort' is used in order to abort the transaction.

int vltranabort(VILLA *villa);
    `villa' specifies a database handle connected as a writer. If successful, the return value is true, else, it is false. Updating a database in the transaction is discarded when it is aborted. The state of the database is rollbacked to before transaction.

The function `vlremove' is used in order to remove a database file.

int vlremove(const char *name);
    `name' specifies the name of a database file. If successful, the return value is true, else, it is false.

The function `vleconv' is used in order to convert a database file for another platform with different byte order.

int vleconv(const char *name, int big);
    `name' specifies the name of a database file. `big' specifies whether the result is for big endian or not. If successful, the return value is true, else, it is false. As contents of each record are not converted, applications are responsible for it.

Although each function of Villa is not reentrant, it does not use any static object internally. So, it can be used as a thread-safe function if each calling and reference to the external variable `dpecode' are under exclusion control, on the assumption that `errno', `malloc', and so on are thread-safe.

Vista is the extended API of Villa. To compensate for the defect that Villa can not handle a file whose size is more than 2GB, Vista does not use Depot but Curia for handling its internal database. While Vista provodes data structure and operations of B+ tree as with Villa, its database is realized as a directory.

In order to use Vista, you should include `vista.h' instead of `villa.h'. Because Vista is implemented by overriding symbols of Villa, it can be used as with Villa. That is, Signatures of Villa and Vista is all the same. However, as its adverse effect, modules using Vista can not use Depot nor Villa.

SEE ALSO

qdbm(3), depot(3), curia(3), relic(3), hovel(3), cabin(3), odeum(3), ndbm(3), gdbm(3)