libpmemkv_config - Man Page

Configuration API for libpmemkv

Synopsis

#include <libpmemkv.h>

pmemkv_config *pmemkv_config_new(void);
void pmemkv_config_delete(pmemkv_config *config);

int pmemkv_config_put_size(pmemkv_config *config, uint64_t value);
int pmemkv_config_put_path(pmemkv_config *config, const char *value);
int **deprecated** pmemkv_config_put_force_create(pmemkv_config *config,
                               bool value);
int pmemkv_config_put_create_or_error_if_exists(pmemkv_config *config, bool value);
int pmemkv_config_put_create_if_missing(pmemkv_config *config, bool value)
int pmemkv_config_put_comparator(pmemkv_config *config, pmemkv_comparator *comparator);
int pmemkv_config_put_oid(pmemkv_config *config, PMEMoid *oid);

int pmemkv_config_put_data(pmemkv_config *config, const char *key, const void *value,
            size_t value_size);
int pmemkv_config_put_object(pmemkv_config *config, const char *key, void *value,
            void (*deleter)(void *));
int pmemkv_config_put_object_cb(pmemkv_config *config, const char *key, void *value,
                void *(*getter)(void *), void (*deleter)(void *));
int pmemkv_config_put_uint64(pmemkv_config *config, const char *key, uint64_t value);
int pmemkv_config_put_int64(pmemkv_config *config, const char *key, int64_t value);
int pmemkv_config_put_string(pmemkv_config *config, const char *key, const char *value);

int pmemkv_config_get_data(pmemkv_config *config, const char *key, const void **value,
            size_t *value_size);
int pmemkv_config_get_object(pmemkv_config *config, const char *key, void **value);
int pmemkv_config_get_uint64(pmemkv_config *config, const char *key, uint64_t *value);
int pmemkv_config_get_int64(pmemkv_config *config, const char *key, int64_t *value);
int pmemkv_config_get_string(pmemkv_config *config, const char *key, const char **value);

pmemkv_comparator *pmemkv_comparator_new(pmemkv_compare_function *fn, const char *name,
                     void *arg);
void pmemkv_comparator_delete(pmemkv_comparator *comparator);

For general description of pmemkv and available engines see libpmemkv(7). For description of pmemkv core API see libpmemkv(3).

Description

pmemkv database is configured using pmemkv_config structure. It stores mappings of keys (null-terminated strings) to values. A value can be:

It also delivers methods to store and read configuration items provided by a user. Once the configuration object is set (with all required parameters), it can be passed to pmemkv_open() method.

List of options which are required by pmemkv database is specific to an engine. Every engine has documented all supported config parameters (please see libpmemkv(7) for details).

pmemkv_config *pmemkv_config_new(void);

Creates an instance of configuration for pmemkv database. On failure, NULL is returned.

void pmemkv_config_delete(pmemkv_config *config);

Deletes pmemkv_config. Should be called ONLY for configs which were not passed to pmemkv_open (as this function moves ownership of the config to the database).

int pmemkv_config_put_size(pmemkv_config *config, uint64_t value);

Puts value to a config at key size, it’s required when creating new database pool. This function provides type safety for size parameter.

int pmemkv_config_put_path(pmemkv_config *config, const char *value);

Puts value to a config at key path. It’s a path to a database file or to a poolset file (see poolset(5) for details), to open or create. Note that when using poolset file, size should be 0. This function provides type safety for path parameter.

int pmemkv_config_put_force_create(pmemkv_config *config, bool value);

It is deprecated and kept for compatibility. It’s an alias for pmemkv_config_put_create_or_error_if_exists - use it instead.

int pmemkv_config_put_create_or_error_if_exists(pmemkv_config *config, bool value);

Puts value to a config at key create_or_error_if_exists. This flag is mutually exclusive with create_if_missing. It works only with engines supporting this flag and it means: If true: pmemkv creates the pool, unless it exists - then it fails. If false: pmemkv opens the pool, unless the path does not exist - then it fails. False by default.

int pmemkv_config_put_create_if_missing(pmemkv_config *config, bool value)

Puts value to a config at key create_if_missing. This flag is mutually exclusive with create_or_error_if_exists. It works only with engines supporting this flag and it means: If true: pmemkv tries to open the pool and if that doesn’t succeed it means there’s (most likely) no pool to use, so it tries to create it. If false: pmemkv opens the pool, unless the path does not exist - then it fails. False by default.

int pmemkv_config_put_comparator(pmemkv_config *config, pmemkv_comparator *comparator);

Puts comparator object to a config. To create an instance of pmemkv_comparator object, pmemkv_comparator_new() function should be used.

int pmemkv_config_put_oid(pmemkv_config *config, PMEMoid *oid);

Puts PMEMoid object to a config (for details see libpmemkv(7)).

int pmemkv_config_put_uint64(pmemkv_config *config, const char *key, uint64_t value);

Puts uint64_t value value to pmemkv_config at key key.

int pmemkv_config_put_int64(pmemkv_config *config, const char *key, int64_t value);

Puts int64_t value value to pmemkv_config at key key.

int pmemkv_config_put_string(pmemkv_config *config, const char *key, const char *value);

Puts null-terminated string to pmemkv_config. The string is copied to the config.

int pmemkv_config_put_data(pmemkv_config *config, const char *key, const void *value, size_t value_size);

Puts copy of binary data pointed by value to pmemkv_config. value_size specifies size of the data.

int pmemkv_config_put_object(pmemkv_config *config, const char *key, void *value, void (*deleter)(void *));

Puts value to pmemkv_config. value can point to arbitrary object. deleter parameter specifies function which will be called for value when the config is destroyed (using pmemkv_config_delete).

int pmemkv_config_put_object_cb(pmemkv_config *config, const char *key, void *value, void *(*getter)(void *), void (*deleter)(void *));

Extended version of pmemkv_config_put_object. It accepts one additional argument - a getter callback. This callback interprets the custom object (value) and returns a pointer which is expected by pmemkv.

Calling pmemkv_config_put_object_cb with getter implemented as:

void *getter(void *arg) { return arg; }

is equivalent to calling pmemkv_config_put_object.

int pmemkv_config_get_uint64(pmemkv_config *config, const char *key, uint64_t *value);

Gets value of a config item with key key. Value is copied to variable pointed by value.

int pmemkv_config_get_int64(pmemkv_config *config, const char *key, int64_t *value);

Gets value of a config item with key key. Value is copied to variable pointed by value.

int pmemkv_config_get_string(pmemkv_config *config, const char *key, const char **value);

Gets pointer to a null-terminated string. The string is not copied. After successful call value points to string stored in pmemkv_config.

int pmemkv_config_get_data(pmemkv_config *config, const char *key, const void **value, size_t *value_size);

Gets pointer to binary data. Data is not copied. After successful call *value points to data stored in pmemkv_config and value_size holds size of the data.

int pmemkv_config_get_object(pmemkv_config *config, const char *key, const void **value);

Gets pointer to an object. After successful call, *value points to the object.

Config items stored in pmemkv_config, which were put using a specific function can be obtained only using corresponding pmemkv_config_get_ function (for example, config items put using pmemkv_config_put_object can only be obtained using pmemkv_config_get_object). Exception from this rule are functions for uint64 and int64. If value put by pmemkv_config_put_int64 is in uint64_t range it can be obtained using pmemkv_config_get_uint64 and vice versa.

pmemkv_comparator *pmemkv_comparator_new(pmemkv_compare_function *fn, const char *name, void *arg);

Creates instance of a comparator object. Accepts comparison function fn, name and arg. In case of persistent engines,nameis stored within the engine. Attempt to open a database which was createad with different comparator of different name will fail with PMEMKV_STATUS_COMPARATOR_MISMATCH.arg` is saved in the comparator and passed to a comparison function on each invocation.

Neither fn nor name can be NULL.

fn should perform a three-way comparison. Return values: * negative value if the first key is less than the second one * zero if both keys are the same * positive value if the first key is greater than the second one

The comparison function should be thread safe - it can be called from multiple threads.

On failure, NULL is returned.

void pmemkv_comparator_delete(pmemkv_comparator *comparator);

Removes the comparator object. Should be called ONLY for comparators which were not put to config (as config takes ownership of the comparator).

To set a comparator for the database use pmemkv_config_put_object:

pmemkv_comparator *cmp = pmemkv_comparator_new(&compare_fn, "my_comparator", NULL);

pmemkv_config_put_object(cfg, "comparator", cmp, (void (*)(void *)) & pmemkv_comparator_delete);

Errors

Each function, except for pmemkv_config_new() and pmemkv_config_delete(), returns status. Possible return values are:

  • PMEMKV_STATUS_OK – no error
  • PMEMKV_STATUS_UNKNOWN_ERROR – unknown error
  • PMEMKV_STATUS_NOT_FOUND – record (or config item) not found
  • PMEMKV_STATUS_CONFIG_PARSING_ERROR – parsing data to config failed
  • PMEMKV_STATUS_CONFIG_TYPE_ERROR – config item has different type than expected

Example

The following examples are taken from examples/pmemkv_config_c directory.

Basic Example

Usage of basic config functions to set parameters based on their functionalities, e.g. pmemkv_config_put_path() or pmemkv_config_put_size().

#include <assert.h>
#include <libpmemkv.h>
#include <libpmemobj/pool_base.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ASSERT(expr)                                                                     \
    do {                                                                             \
        if (!(expr))                                                             \
            puts(pmemkv_errormsg());                                         \
        assert(expr);                                                            \
    } while (0)

static const uint64_t SIZE = 1024UL * 1024UL * 1024UL;

int key_length_compare(const char *key1, size_t keybytes1, const char *key2,
               size_t keybytes2, void *arg)
{
    if (keybytes2 < keybytes1)
        return -1;
    else if (keybytes2 > keybytes1)
        return 1;
    else
        return 0;
}

int main(int argc, char *argv[])
{
    if (argc < 2) {
        fprintf(stderr, "Usage: %s file\n", argv[0]);
        exit(1);
    }

    /* Create config */
    pmemkv_config *config = pmemkv_config_new();
    ASSERT(config != NULL);

    /* Add path parameter to config. Meaning of this is dependent on chosen engine.
     *  E.g. if config is used with cmap engine,
     *  it is a path to a database file or to a poolset file. However for
     *  vcmap it is a path to an existing directory */
    int status = pmemkv_config_put_path(config, argv[1]);
    ASSERT(status == PMEMKV_STATUS_OK);

    /* Specifies size of the database */
    status = pmemkv_config_put_size(config, SIZE);
    ASSERT(status == PMEMKV_STATUS_OK);

    /* Specifies value of create_if_missing flag.
     * Alternatively, another flag - 'create_or_error_if_exists' can be set using:
     * `pmemkv_config_put_create_or_error_if_exists`
     * For differences between the two, see manpage libpmemkv(7). */
    status = pmemkv_config_put_create_if_missing(config, true);
    ASSERT(status == PMEMKV_STATUS_OK);

    /* Specifies comparator used by the engine */
    pmemkv_comparator *cmp =
        pmemkv_comparator_new(&key_length_compare, "key_length_compare", NULL);
    ASSERT(cmp != NULL);
    status = pmemkv_config_put_comparator(config, cmp);
    ASSERT(status == PMEMKV_STATUS_OK);

    /* Adds pointer to oid (for details see libpmemkv(7)) to the config */
    PMEMoid oid;
    status = pmemkv_config_put_oid(config, &oid);
    ASSERT(status == PMEMKV_STATUS_OK);

    pmemkv_config_delete(config);

    return 0;
}

Type Based Configuration Example

Usage of config functions to set and get data based on their data type, e.g. pmemkv_config_put_int64() or pmemkv_config_put_object().

#include <assert.h>
#include <libpmemkv.h>
#include <libpmemkv_json_config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define ASSERT(expr)                                                                     \
    do {                                                                             \
        if (!(expr))                                                             \
            puts(pmemkv_errormsg());                                         \
        assert(expr);                                                            \
    } while (0)

/* deleter for int pointer */
void free_int_ptr(void *ptr)
{
    free(ptr);
}

int main()
{
    pmemkv_config *config = pmemkv_config_new();
    ASSERT(config != NULL);

    /* Put int64_t value */
    int status = pmemkv_config_put_int64(config, "size", 1073741824);
    ASSERT(status == PMEMKV_STATUS_OK);

    char buffer[] = "ABC";

    /* Put binary data stored in buffer */
    status = pmemkv_config_put_data(config, "binary", buffer, 3);
    ASSERT(status == PMEMKV_STATUS_OK);

    const void *data;
    size_t data_size;

    /* Get pointer to binary data stored in config */
    status = pmemkv_config_get_data(config, "binary", &data, &data_size);
    ASSERT(status == PMEMKV_STATUS_OK);
    ASSERT(data_size == 3);
    ASSERT(((const char *)data)[0] == 'A');

    int *int_ptr = malloc(sizeof(int));
    ASSERT(int_ptr != NULL);
    *int_ptr = 10;

    /* Put pointer to dynamically allocated object, free_int_ptr is called on
     * pmemkv_config_delete */
    status = pmemkv_config_put_object(config, "int_ptr", int_ptr, &free_int_ptr);
    ASSERT(status == PMEMKV_STATUS_OK);

    int *get_int_ptr;

    /* Get pointer to object stored in config */
    status = pmemkv_config_get_object(config, "int_ptr", (void **)&get_int_ptr);
    ASSERT(status == PMEMKV_STATUS_OK);
    ASSERT(*get_int_ptr == 10);

    pmemkv_config_delete(config);

    pmemkv_config *config_from_json = pmemkv_config_new();
    ASSERT(config_from_json != NULL);

    /* Parse JSON and put all items found into config_from_json */
    status = pmemkv_config_from_json(config_from_json, "{\"path\":\"/dev/shm\",\
         \"size\":1073741824,\
         \"subconfig\":{\
            \"size\":1073741824\
            }\
        }");
    ASSERT(status == PMEMKV_STATUS_OK);

    const char *path;
    status = pmemkv_config_get_string(config_from_json, "path", &path);
    ASSERT(status == PMEMKV_STATUS_OK);
    ASSERT(strcmp(path, "/dev/shm") == 0);

    pmemkv_config *subconfig;

    /* Get pointer to nested configuration "subconfig" */
    status = pmemkv_config_get_object(config_from_json, "subconfig",
                      (void **)&subconfig);
    ASSERT(status == PMEMKV_STATUS_OK);

    size_t sub_size;
    status = pmemkv_config_get_uint64(subconfig, "size", &sub_size);
    ASSERT(status == PMEMKV_STATUS_OK);
    ASSERT(sub_size == 1073741824);

    pmemkv_config_delete(config_from_json);

    return 0;
}

See Also

libpmemkv(7), libpmemkv(3) , libpmemkv_json_config(3) and <https://pmem.io>

Referenced By

libpmemkv(3), libpmemkv(7), libpmemkv_iterator(3), libpmemkv_json_config(3), libpmemkv_tx(3).

The man pages pmemkv_comparator_delete(3), pmemkv_comparator_new(3), pmemkv_config_delete(3), pmemkv_config_get_data(3), pmemkv_config_get_int64(3), pmemkv_config_get_object(3), pmemkv_config_get_string(3), pmemkv_config_get_uint64(3), pmemkv_config_new(3), pmemkv_config_put_comparator(3), pmemkv_config_put_create_if_missing(3), pmemkv_config_put_create_or_error_if_exists(3), pmemkv_config_put_data(3), pmemkv_config_put_force_create(3), pmemkv_config_put_int64(3), pmemkv_config_put_object(3), pmemkv_config_put_object_cb(3), pmemkv_config_put_oid(3), pmemkv_config_put_path(3), pmemkv_config_put_size(3), pmemkv_config_put_string(3) and pmemkv_config_put_uint64(3) are aliases of libpmemkv_config(3).

2021-07-30 PMEMKV - pmemkv version 1.5.0 PMEMKV Programmer's Manual