Provided by: libpmemkv-dev_1.5.0-5_amd64 bug

NAME

       pmemkv - Key/Value Datastore for Persistent Memory

SYNOPSIS

              #include <libpmemkv.h>

              typedef int pmemkv_get_kv_callback(const char *key, size_t keybytes, const char *value,
                          size_t valuebytes, void *arg);
              typedef void pmemkv_get_v_callback(const char *value, size_t valuebytes, void *arg);

              int pmemkv_open(const char *engine, pmemkv_config *config, pmemkv_db **db);
              void pmemkv_close(pmemkv_db *kv);

              int pmemkv_count_all(pmemkv_db *db, size_t *cnt);
              int pmemkv_count_above(pmemkv_db *db, const char *k, size_t kb, size_t *cnt);
              int pmemkv_count_below(pmemkv_db *db, const char *k, size_t kb, size_t *cnt);
              int pmemkv_count_between(pmemkv_db *db, const char *k1, size_t kb1, const char *k2,
                          size_t kb2, size_t *cnt);

              int pmemkv_get_all(pmemkv_db *db, pmemkv_get_kv_callback *c, void *arg);
              int pmemkv_get_above(pmemkv_db *db, const char *k, size_t kb, pmemkv_get_kv_callback *c,
                          void *arg);
              int pmemkv_get_below(pmemkv_db *db, const char *k, size_t kb, pmemkv_get_kv_callback *c,
                          void *arg);
              int pmemkv_get_between(pmemkv_db *db, const char *k1, size_t kb1, const char *k2,
                          size_t kb2, pmemkv_get_kv_callback *c, void *arg);

              int pmemkv_exists(pmemkv_db *db, const char *k, size_t kb);

              int pmemkv_get(pmemkv_db *db, const char *k, size_t kb, pmemkv_get_v_callback *c,
                          void *arg);
              int pmemkv_get_copy(pmemkv_db *db, const char *k, size_t kb, char *buffer,
                          size_t buffer_size, size_t *value_size);
              int pmemkv_put(pmemkv_db *db, const char *k, size_t kb, const char *v, size_t vb);

              int pmemkv_remove(pmemkv_db *db, const char *k, size_t kb);

              int pmemkv_defrag(pmemkv_db *db, double start_percent, double amount_percent);

              const char *pmemkv_errormsg(void);

       For pmemkv configuration API description see libpmemkv_config(3).  For pmemkv iterator API
       description  see  libpmemkv_iterator(3).    For   general   pmemkv   information,   engine
       descriptions and bindings details see libpmemkv(7).

DESCRIPTION

       Keys  and  values stored in a pmemkv database can be arbitrary binary data and can contain
       multiple null characters.  Every function which accepts key expects const char *k  pointer
       to data and its size as size_t.

       Some of the functions (mainly range-query API) are not guaranteed to be implemented by all
       engines.   If  an  engine  does  not  support  a  certain   function,   it   will   return
       PMEMKV_STATUS_NOT_SUPPORTED.

       Note:  There  are no explicit upper_bound/lower_bound functions.  If you want to obtain an
       element(s)  above  or  below  the  selected  key,  you  can  use   pmemkv_get_above()   or
       pmemkv_get_below().  See descriptions of these functions for details.

       int pmemkv_open(const char *engine, pmemkv_config *config, pmemkv_db **db);
              Opens the pmemkv database and stores a pointer to a pmemkv_db instance in *db.  The
              engine parameter specifies the engine  name  (see  libpmemkv(7)  for  the  list  of
              available   engines).    The   config   parameter   specifies   configuration  (see
              libpmemkv_config(3) for details).  Pmemkv takes ownership of the config parameter -
              this means that pmemkv_config_delete() must NOT be called after open (successful or
              failed).

       void pmemkv_close(pmemkv_db *kv);
              Closes pmemkv database.

       int pmemkv_count_all(pmemkv_db *db, size_t *cnt);
              Stores in *cnt the number of records in db.

       int pmemkv_count_above(pmemkv_db *db, const char *k, size_t kb, size_t *cnt);
              Stores in *cnt the number of records in db whose keys are greater than the key k of
              length kb.  Order of the elements is specified by a comparator (see libpmemkv(7)).

       int pmemkv_count_below(pmemkv_db *db, const char *k, size_t kb, size_t *cnt);
              Stores  in  *cnt  the number of records in db whose keys are less than the key k of
              length kb.  Order of the elements is specified by a comparator (see libpmemkv(7)).

       int pmemkv_count_between(pmemkv_db *db, const char *k1, size_t kb1, const char *k2, size_t
       kb2, size_t *cnt);
              Stores  in  *cnt the number of records in db whose keys are greater than key k1 (of
              length kb1) and less than key k2  (of  length  kb2).   Order  of  the  elements  is
              specified by a comparator (see libpmemkv(7)).

       int pmemkv_get_all(pmemkv_db *db, pmemkv_get_kv_callback *c, void *arg);
              Executes  function  c  for  every  record  stored  in  db.  Arguments passed to the
              function are: pointer to a key, size of the key, pointer to a value,  size  of  the
              value  and  arg  specified by the user.  Function c can stop iteration by returning
              non-zero value.  In that case pmemkv_get_all() returns PMEMKV_STATUS_STOPPED_BY_CB.
              Returning  0  continues  iteration.   Order  of  the  elements  is  specified  by a
              comparator (see libpmemkv(7)).

       int pmemkv_get_above(pmemkv_db *db, const char *k, size_t kb,  pmemkv_get_kv_callback  *c,
       void *arg);
              Executes function c for every record stored in db whose keys are greater than key k
              (of length kb).  Arguments passed to c are: pointer to a  key,  size  of  the  key,
              pointer  to  a  value, size of the value and arg specified by the user.  Function c
              can stop iteration by returning non-zero value.  In  that  case  pmemkv_get_above()
              returns  PMEMKV_STATUS_STOPPED_BY_CB.   Returning  0 continues iteration.  Order of
              the elements is specified by a comparator (see libpmemkv(7)).

       int pmemkv_get_below(pmemkv_db *db, const char *k, size_t kb,  pmemkv_get_kv_callback  *c,
       void *arg);
              Executes  function  c  for every record stored in db whose keys are less than key k
              (of length kb).  Arguments passed to c are: pointer to a  key,  size  of  the  key,
              pointer  to  a  value, size of the value and arg specified by the user.  Function c
              can stop iteration by returning non-zero value.  In  that  case  pmemkv_get_below()
              returns  PMEMKV_STATUS_STOPPED_BY_CB.   Returning  0 continues iteration.  Order of
              the elements is specified by a comparator (see libpmemkv(7)).

       int pmemkv_get_between(pmemkv_db *db, const char *k1, size_t kb1, const char  *k2,  size_t
       kb2, pmemkv_get_kv_callback *c, void *arg);
              Executes  function  c for every record stored in db whose keys are greater than key
              k1 (of length kb1) and less than key k2 (of length kb2).   Arguments  passed  to  c
              are:  pointer  to a key, size of the key, pointer to a value, size of the value and
              arg specified by the user.  Function c can stop  iteration  by  returning  non-zero
              value.   In  that  case  pmemkv_get_between()  returns PMEMKV_STATUS_STOPPED_BY_CB.
              Returning 0  continues  iteration.   Order  of  the  elements  is  specified  by  a
              comparator (see libpmemkv(7)).

       int pmemkv_exists(pmemkv_db *db, const char *k, size_t kb);
              Checks  existence  of  record  with  key  k  of  length  kb.   If record is present
              PMEMKV_STATUS_OK is returned, otherwise PMEMKV_STATUS_NOT_FOUND is returned.  Other
              possible return values are described in the ERRORS section.

       int  pmemkv_get(pmemkv_db  *db,  const  char *k, size_t kb, pmemkv_get_v_callback *c, void
       *arg);
              Executes function c on record with key k (of length kb).  If record is present  and
              no  error occurred the function returns PMEMKV_STATUS_OK.  If record does not exist
              PMEMKV_STATUS_NOT_FOUND is returned.  Other possible return values are described in
              the ERRORS section.  Function c is called with the following parameters: pointer to
              a value, size of the value and arg specified by the  user.   Value  points  to  the
              location  where  data  is  actually  stored  (no  copy  occurs).   This function is
              guaranteed to be implemented by all engines.

       int pmemkv_get_copy(pmemkv_db  *db,  const  char  *k,  size_t  kb,  char  *buffer,  size_t
       buffer_size, size_t *value_size);
              Copies  value  of  record  with key k of length kb to user provided buffer.  buffer
              points to the value buffer, buffer_size  specifies  its  size  and  *value_size  is
              filled  in  by this function.  If the value doesn’t fit in the provided buffer then
              this function returns PMEMKV_STATUS_UNKNOWN_ERROR.  Otherwise, in  absence  of  any
              errors,  PMEMKV_STATUS_OK  is returned.  Other possible return values are described
              in the ERRORS section.  This function  is  guaranteed  to  be  implemented  by  all
              engines.

       int pmemkv_put(pmemkv_db *db, const char *k, size_t kb, const char *v, size_t vb);
              Inserts a key-value pair into pmemkv database.  kb is the length of key k and vb is
              the length of value v.  When this function returns, caller is free  to  reuse  both
              buffers.  This function is guaranteed to be implemented by all engines.

       int pmemkv_remove(pmemkv_db *db, const char *k, size_t kb);
              Removes  record  with  key  k  of  length  kb.   This  function is guaranteed to be
              implemented by all engines.

       int pmemkv_defrag(pmemkv_db *db, double start_percent, double amount_percent);
              Defragments approximately `amount_percent' percent  of  elements  in  the  database
              starting from `start_percent' percent of elements.

       const char *pmemkv_errormsg(void);
              Returns a human readable string describing the last error.

   ERRORS
       Each  function,  except  for  pmemkv_close()  and  pmemkv_errormsg(),  returns  one of the
       following status codes:

       • PMEMKV_STATUS_OK – no error

       • PMEMKV_STATUS_UNKNOWN_ERROR – unknown error

       • PMEMKV_STATUS_NOT_FOUND – record not found

       • PMEMKV_STATUS_NOT_SUPPORTED – function is not implemented by current engine

       • PMEMKV_STATUS_INVALID_ARGUMENT – argument to function has wrong value

       • PMEMKV_STATUS_CONFIG_PARSING_ERROR – parsing data to config failed

       • PMEMKV_STATUS_CONFIG_TYPE_ERROR – config item has different type than expected

       • PMEMKV_STATUS_STOPPED_BY_CB – iteration was stopped by user’s callback

       • PMEMKV_STATUS_OUT_OF_MEMORY – operation failed because there is not  enough  memory  (or
         space on the device)

       • PMEMKV_STATUS_WRONG_ENGINE_NAME – engine name does not match any available engine

       • PMEMKV_STATUS_TRANSACTION_SCOPE_ERROR  –  an  error  with  the  scope  of the libpmemobj
         transaction

       • PMEMKV_STATUS_DEFRAG_ERROR – the defragmentation process failed (possibly in the  middle
         of a run)

       Status  returned  from  a  function  can change in a future version of a library to a more
       specific one.  For example, if  a  function  returns  PMEMKV_STATUS_UNKNOWN_ERROR,  it  is
       possible   that   in   future  versions  it  will  return  PMEMKV_STATUS_INVALID_ARGUMENT.
       Recommended way to check for an error is to compare status with PMEMKV_STATUS_OK.

EXAMPLE

       The following example is taken from examples/pmemkv_basic_c directory.

       Basic pmemkv usage in C:

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

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

              #define LOG(msg) puts(msg)
              #define MAX_VAL_LEN 64

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

              int get_kv_callback(const char *k, size_t kb, const char *value, size_t value_bytes,
                          void *arg)
              {
                  printf("   visited: %s\n", k);

                  return 0;
              }

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

                  /* See libpmemkv_config(3) for more detailed example of config creation */
                  LOG("Creating config");
                  pmemkv_config *cfg = pmemkv_config_new();
                  ASSERT(cfg != NULL);

                  int s = pmemkv_config_put_path(cfg, argv[1]);
                  ASSERT(s == PMEMKV_STATUS_OK);
                  s = pmemkv_config_put_size(cfg, SIZE);
                  ASSERT(s == PMEMKV_STATUS_OK);
                  s = pmemkv_config_put_create_if_missing(cfg, true);
                  ASSERT(s == PMEMKV_STATUS_OK);

                  /* Alternatively create_or_error_if_exists flag can be set, to fail if file exists
                   * For differences between the two flags, see manpage libpmemkv(7). */
                  /* s = pmemkv_config_put_create_or_error_if_exists(cfg, true); */

                  LOG("Opening pmemkv database with 'cmap' engine");
                  pmemkv_db *db = NULL;
                  s = pmemkv_open("cmap", cfg, &db);
                  ASSERT(s == PMEMKV_STATUS_OK);
                  ASSERT(db != NULL);

                  LOG("Putting new key");
                  const char *key1 = "key1";
                  const char *value1 = "value1";
                  s = pmemkv_put(db, key1, strlen(key1), value1, strlen(value1));
                  ASSERT(s == PMEMKV_STATUS_OK);

                  size_t cnt;
                  s = pmemkv_count_all(db, &cnt);
                  ASSERT(s == PMEMKV_STATUS_OK);
                  ASSERT(cnt == 1);

                  LOG("Reading key back");
                  char val[MAX_VAL_LEN];
                  s = pmemkv_get_copy(db, key1, strlen(key1), val, MAX_VAL_LEN, NULL);
                  ASSERT(s == PMEMKV_STATUS_OK);
                  ASSERT(!strcmp(val, "value1"));

                  LOG("Iterating existing keys");
                  const char *key2 = "key2";
                  const char *value2 = "value2";
                  const char *key3 = "key3";
                  const char *value3 = "value3";
                  pmemkv_put(db, key2, strlen(key2), value2, strlen(value2));
                  pmemkv_put(db, key3, strlen(key3), value3, strlen(value3));
                  pmemkv_get_all(db, &get_kv_callback, NULL);

                  LOG("Removing existing key");
                  s = pmemkv_remove(db, key1, strlen(key1));
                  ASSERT(s == PMEMKV_STATUS_OK);
                  ASSERT(pmemkv_exists(db, key1, strlen(key1)) == PMEMKV_STATUS_NOT_FOUND);

                  LOG("Defragmenting the database");
                  s = pmemkv_defrag(db, 0, 100);
                  ASSERT(s == PMEMKV_STATUS_OK);

                  LOG("Closing database");
                  pmemkv_close(db);

                  return 0;
              }

   Common usage mistake
       Common mistake in pmemkv API usage (especially when  using  C++  API)  is  to  dereference
       pointer to the data stored in pmemkv outside of a callback function scope.

              std::string value;
              const char* ptr;
              size_t sz;
              kv->get("key1", [&](string_view v) {
                  /* Save pointer to the data to use it later outside of a callback scope */
                  ptr = v.data();
                  sz = v.size();
              });
              kv->remove("key");
              /* ERROR!
               * Using this pointer outside of a callback function may cause access to some random data
               * or a segmentation fault. At that point, ptr should be considered as invalid.
               */
              value.append(ptr, sz);

SEE ALSO

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