hamsterdb Database Configuration
[hamsterdb Database Functions]

Modules

 hamsterdb Database Information Request Parameters
 hamsterdb Hinting Flags for Find, Insert,

Defines

#define HAM_PARAM_CACHESIZE   0x00000100
#define HAM_PARAM_PAGESIZE   0x00000101
#define HAM_PARAM_KEYSIZE   0x00000102
#define HAM_PARAM_MAX_ENV_DATABASES   0x00000103
#define HAM_PARAM_DATA_ACCESS_MODE   0x00000104
#define HAM_OVERWRITE   0x0001
#define HAM_DUPLICATE   0x0002
#define HAM_DUPLICATE_INSERT_BEFORE   0x0004
#define HAM_DUPLICATE_INSERT_AFTER   0x0008
#define HAM_DUPLICATE_INSERT_FIRST   0x0010
#define HAM_DUPLICATE_INSERT_LAST   0x0020
#define HAM_DIRECT_ACCESS   0x0040
#define HAM_PARTIAL   0x0080
#define HAM_FAST_ESTIMATE   0x0001
#define HAM_AUTO_CLEANUP   1
#define HAM_DONT_CLEAR_LOG   2
#define HAM_TXN_AUTO_ABORT   4
#define HAM_TXN_AUTO_COMMIT   8

Typedefs

typedef int HAM_CALLCONV(* ham_prefix_compare_func_t )(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, ham_size_t lhs_real_length, const ham_u8_t *rhs, ham_size_t rhs_length, ham_size_t rhs_real_length)
typedef int HAM_CALLCONV(* ham_compare_func_t )(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, const ham_u8_t *rhs, ham_size_t rhs_length)
typedef int HAM_CALLCONV(* ham_duplicate_compare_func_t )(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, const ham_u8_t *rhs, ham_size_t rhs_length)

Functions

HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_get_parameters (ham_db_t *db, ham_parameter_t *param)
HAM_EXPORT ham_u32_t HAM_CALLCONV ham_get_flags (ham_db_t *db)
HAM_EXPORT ham_env_t *HAM_CALLCONV ham_get_env (ham_db_t *db)
HAM_EXPORT int HAM_CALLCONV ham_key_get_approximate_match_type (ham_key_t *key)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_get_error (ham_db_t *db)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_set_prefix_compare_func (ham_db_t *db, ham_prefix_compare_func_t foo)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_set_compare_func (ham_db_t *db, ham_compare_func_t foo)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_set_duplicate_compare_func (ham_db_t *db, ham_duplicate_compare_func_t foo)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_enable_compression (ham_db_t *db, ham_u32_t level, ham_u32_t flags)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_find (ham_db_t *db, ham_txn_t *txn, ham_key_t *key, ham_record_t *record, ham_u32_t flags)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_insert (ham_db_t *db, ham_txn_t *txn, ham_key_t *key, ham_record_t *record, ham_u32_t flags)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_erase (ham_db_t *db, ham_txn_t *txn, ham_key_t *key, ham_u32_t flags)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_flush (ham_db_t *db, ham_u32_t flags)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_get_key_count (ham_db_t *db, ham_txn_t *txn, ham_u32_t flags, ham_offset_t *keycount)
HAM_EXPORT ham_status_t
HAM_CALLCONV 
ham_close (ham_db_t *db, ham_u32_t flags)

Detailed Description

Parameters

See also:
ham_parameter_t

Define Documentation

#define HAM_AUTO_CLEANUP   1

Flag for ham_close, ham_env_close

Definition at line 2208 of file hamsterdb.h.

#define HAM_DIRECT_ACCESS   0x0040

Flag for ham_find, ham_cursor_find_ex, ham_cursor_move

Definition at line 2026 of file hamsterdb.h.

#define HAM_DONT_CLEAR_LOG   2

Definition at line 2211 of file hamsterdb.h.

#define HAM_DUPLICATE   0x0002

Flag for ham_insert and ham_cursor_insert

Definition at line 2011 of file hamsterdb.h.

#define HAM_DUPLICATE_INSERT_AFTER   0x0008

Flag for ham_cursor_insert

Definition at line 2017 of file hamsterdb.h.

#define HAM_DUPLICATE_INSERT_BEFORE   0x0004

Flag for ham_cursor_insert

Definition at line 2014 of file hamsterdb.h.

#define HAM_DUPLICATE_INSERT_FIRST   0x0010

Flag for ham_cursor_insert

Definition at line 2020 of file hamsterdb.h.

#define HAM_DUPLICATE_INSERT_LAST   0x0020

Flag for ham_cursor_insert

Definition at line 2023 of file hamsterdb.h.

#define HAM_FAST_ESTIMATE   0x0001

Flag for ham_get_key_count

Definition at line 2165 of file hamsterdb.h.

#define HAM_OVERWRITE   0x0001

Flag for ham_insert and ham_cursor_insert

When specified with ham_insert and in case a key is specified which stores duplicates in the Database, the first duplicate record will be overwritten.

When used with ham_cursor_insert and assuming the same conditions, the duplicate currently referenced by the Cursor will be overwritten.

Definition at line 2008 of file hamsterdb.h.

#define HAM_PARAM_CACHESIZE   0x00000100

Parameter name for ham_open_ex, ham_create_ex; sets the cache size

Definition at line 1477 of file hamsterdb.h.

#define HAM_PARAM_DATA_ACCESS_MODE   0x00000104

Parameter name for ham_create_ex, ham_open_ex; set the expected access mode.

Definition at line 1493 of file hamsterdb.h.

#define HAM_PARAM_KEYSIZE   0x00000102

Parameter name for ham_create_ex; sets the key size

Definition at line 1484 of file hamsterdb.h.

#define HAM_PARAM_MAX_ENV_DATABASES   0x00000103

Parameter name for ham_env_create_ex; sets the number of maximum Databases

Definition at line 1488 of file hamsterdb.h.

#define HAM_PARAM_PAGESIZE   0x00000101

Parameter name for ham_open_ex, ham_create_ex; sets the page size

Definition at line 1481 of file hamsterdb.h.

#define HAM_PARTIAL   0x0080

Flag for ham_insert, ham_cursor_insert, ham_find, ham_find_ex, ham_cursor_move

Definition at line 2030 of file hamsterdb.h.

#define HAM_TXN_AUTO_ABORT   4

Automatically abort all open Transactions (the default)

Definition at line 2214 of file hamsterdb.h.

#define HAM_TXN_AUTO_COMMIT   8

Automatically commit all open Transactions

Definition at line 2217 of file hamsterdb.h.


Typedef Documentation

typedef int HAM_CALLCONV(* ham_compare_func_t)(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, const ham_u8_t *rhs, ham_size_t rhs_length)

Typedef for a key comparison function

Remarks:
This function compares two index keys. It returns -1, if lhs ("left-hand side", the parameter on the left side) is smaller than rhs ("right-hand side"), 0 if both keys are equal, and 1 if lhs is larger than rhs.

Definition at line 1703 of file hamsterdb.h.

typedef int HAM_CALLCONV(* ham_duplicate_compare_func_t)(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, const ham_u8_t *rhs, ham_size_t rhs_length)

Typedef for a record comparison function

Remarks:
This function compares two records. It returns -1, if lhs ("left-hand side", the parameter on the left side) is smaller than rhs ("right-hand side"), 0 if both keys are equal, and 1 if lhs is larger than rhs.
As hamsterdb allows zero-length records, it may happen that either lhs_length or rhs_length, or both are zero. In this case the related data pointers (rhs, lhs) may be NULL.

Definition at line 1744 of file hamsterdb.h.

typedef int HAM_CALLCONV(* ham_prefix_compare_func_t)(ham_db_t *db, const ham_u8_t *lhs, ham_size_t lhs_length, ham_size_t lhs_real_length, const ham_u8_t *rhs, ham_size_t rhs_length, ham_size_t rhs_real_length)

Typedef for a prefix comparison function

Remarks:
This function compares two index keys. It returns -1 if lhs ("left-hand side", the parameter on the left side) is smaller than rhs ("right-hand side"), 0 if both keys are equal, and 1 if lhs is larger than rhs.
If one of the keys is only partially loaded, but the comparison function needs the full key, the return value should be HAM_PREFIX_REQUEST_FULLKEY.

Definition at line 1671 of file hamsterdb.h.


Function Documentation

HAM_EXPORT ham_status_t HAM_CALLCONV ham_close ( ham_db_t db,
ham_u32_t  flags 
)

Closes the Database

This function flushes the Database and then closes the file handle. It does not free the memory resources allocated in the db handle - use ham_delete to free db.

If the flag HAM_AUTO_CLEANUP is specified, hamsterdb automatically calls ham_cursor_close on all open Cursors. This invalidates the ham_cursor_t handle!

If the flag is not specified, the application must close all Database Cursors with ham_cursor_close to prevent memory leaks.

This function removes all record-level filters installed with ham_add_record_filter (and hence also, implicitly, the filter installed by ham_enable_compression).

This function also aborts all Transactions which were not yet committed, and therefore renders all Transaction handles invalid. If the flag HAM_TXN_AUTO_COMMIT is specified, all Transactions will be committed.

Parameters:
db A valid Database handle
flags Optional flags for closing the Database. Possible values are:

Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db is NULL
HAM_CURSOR_STILL_OPEN if not all Cursors of this Database were closed, and HAM_AUTO_CLEANUP was not specified

Referenced by ham::db::close().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_enable_compression ( ham_db_t db,
ham_u32_t  level,
ham_u32_t  flags 
)

Enables zlib compression for all inserted records

This function enables zlib compression for all inserted Database records.

The compression will be active till ham_close is called. If the Database handle is reused after calling ham_close, the compression is no longer active. ham_enable_compression should be called immediately after ham_create[_ex] or ham_open[_ex]. When opening the Database, the compression has to be enabled again.

Note that zlib usually has an overhead and often is not effective if the records are small (i.e. < 128byte), but this highly depends on the data that is inserted.

The zlib compression filter does not allow queries (i.e. with ham_find) with user-allocated records and the flag HAM_RECORD_USER_ALLOC. In this case, the query-function will return HAM_INV_PARAMETER.

Parameters:
db A valid Database handle
level The compression level. 0 for the zlib default, 1 for best speed and 9 for minimum size
flags Optional flags for the compression; unused, set to 0
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db is NULL or level is not between 0 and 9
HAM_NOT_IMPLEMENTED if hamsterdb was compiled without support for compression

Referenced by ham::db::enable_compression().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_erase ( ham_db_t db,
ham_txn_t txn,
ham_key_t key,
ham_u32_t  flags 
)

Erases a Database item

This function erases a Database item. If the item key does not exist, HAM_KEY_NOT_FOUND is returned.

Note that ham_erase can not erase a single duplicate key. If the key has multiple duplicates, all duplicates of this key will be erased. Use ham_cursor_erase to erase a specific duplicate key.

Parameters:
db A valid Database handle
txn A Transaction handle, or NULL
key The key to delete
flags Optional flags for erasing; unused, set to 0
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db or key is NULL
HAM_DB_READ_ONLY if you tried to erase a key from a read-only Database
HAM_KEY_NOT_FOUND if key was not found

Referenced by ham::db::erase().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_find ( ham_db_t db,
ham_txn_t txn,
ham_key_t key,
ham_record_t record,
ham_u32_t  flags 
)

Searches an item in the Database

This function searches the Database for key. If the key is found, record will receive the record of this item and HAM_SUCCESS is returned. If the key is not found, the function returns HAM_KEY_NOT_FOUND.

A ham_record_t structure should be initialized with zeroes before it is being used. This can be done with the C library routines memset(3) or bzero(2).

If the function completes successfully, the record pointer is initialized with the size of the record (in record.size) and the actual record data (in record.data). If the record is empty, size is 0 and data points to NULL.

The data pointer is a temporary pointer and will be overwritten by subsequent hamsterdb API calls. You can alter this behaviour by allocating the data pointer in the application and setting record.flags to HAM_RECORD_USER_ALLOC. Make sure that the allocated buffer is large enough.

When specifying HAM_DIRECT_ACCESS, the data pointer will point directly to the record that is stored in hamsterdb; the data can be modified, but the pointer must not be reallocated of freed. The flag HAM_DIRECT_ACCESS is only allowed in In-Memory Databases.

ham_find can not search for duplicate keys. If key has multiple duplicates, only the first duplicate is returned.

You can read only portions of the record by specifying the flag HAM_PARTIAL. In this case, hamsterdb will read record->partial_size bytes of the record data at offset record->partial_offset. If necessary, the record data will be limited to the original record size. The number of actually read bytes is returned in record->size.

Parameters:
db A valid Database handle
txn A Transaction handle, or NULL
key The key of the item
record The record of the item
flags Optional flags for searching, which can be combined with bitwise OR. Possible flags are:

  • HAM_FIND_EXACT_MATCH (default). If the key exists, the cursor is adjusted to reference the record. Otherwise, an error is returned. Note that for backwards compatibility the value zero (0) can specified as an alternative when this option is not mixed with any of the others in this list.
  • HAM_FIND_LT_MATCH Cursor 'find' flag 'Less Than': the cursor is moved to point at the last record which' key is less than the specified key. When such a record cannot be located, an error is returned.
  • HAM_FIND_GT_MATCH Cursor 'find' flag 'Greater Than': the cursor is moved to point at the first record which' key is larger than the specified key. When such a record cannot be located, an error is returned.
  • HAM_FIND_LEQ_MATCH Cursor 'find' flag 'Less or EQual': the cursor is moved to point at the record which' key matches the specified key and when such a record is not available the cursor is moved to point at the last record which' key is less than the specified key. When such a record cannot be located, an error is returned.
  • HAM_FIND_GEQ_MATCH Cursor 'find' flag 'Greater or Equal': the cursor is moved to point at the record which' key matches the specified key and when such a record is not available the cursor is moved to point at the first record which' key is larger than the specified key. When such a record cannot be located, an error is returned.
  • HAM_FIND_NEAR_MATCH Cursor 'find' flag 'Any Near Or Equal': the cursor is moved to point at the record which' key matches the specified key and when such a record is not available the cursor is moved to point at either the last record which' key is less than the specified key or the first record which' key is larger than the specified key, whichever of these records is located first. When such records cannot be located, an error is returned.
  • HAM_DIRECT_ACCESS Only for In-Memory Databases! Returns a direct pointer to the data blob stored by the hamsterdb engine. This pointer must not be resized or freed, but the data in this memory can be modified.
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db, key or record is NULL
HAM_INV_PARAMETER if HAM_DIRECT_ACCESS is specified, but the Database is not an In-Memory Database.
HAM_KEY_NOT_FOUND if the key does not exist
Remarks:
When either or both HAM_FIND_LT_MATCH and/or HAM_FIND_GT_MATCH have been specified as flags, the key structure will be overwritten when an approximate match was found: the key and record structures will then point at the located key and record. In this case the caller should ensure key points at a structure which must adhere to the same restrictions and conditions as specified for ham_cursor_move(..., HAM_CURSOR_NEXT).
See also:
HAM_RECORD_USER_ALLOC
HAM_KEY_USER_ALLOC
ham_record_t
ham_key_t

Referenced by ham::db::find().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_flush ( ham_db_t db,
ham_u32_t  flags 
)

Flushes the Database

This function flushes the Database cache and writes the whole file to disk. If this Database was opened in an Environment, all other Databases of this Environment are flushed as well.

Since In-Memory Databases do not have a file on disk, the function will have no effect and will return HAM_SUCCESS.

Parameters:
db A valid Database handle
flags Optional flags for flushing; unused, set to 0
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db is NULL

Referenced by ham::db::flush().

HAM_EXPORT ham_env_t* HAM_CALLCONV ham_get_env ( ham_db_t db  ) 

Retrieve the Environment handle of a Database

Every Database belongs to an Environment, even if it was created with ham_create[_ex] or ham_open[_ex].

Therefore this function always returns a valid handle, if the Database handle was also valid and initialized (otherwise it returns NULL).

Parameters:
db A valid Database handle
Returns:
The Environment handle
HAM_EXPORT ham_status_t HAM_CALLCONV ham_get_error ( ham_db_t db  ) 

Returns the last error code

Parameters:
db A valid Database handle
Returns:
The last error code which was returned by one of the hamsterdb API functions. Use ham_strerror to translate this code to a descriptive string

Referenced by ham::db::get_error().

HAM_EXPORT ham_u32_t HAM_CALLCONV ham_get_flags ( ham_db_t db  ) 

Retrieve the flags which were specified when the Database was created or opened

Parameters:
db A valid Database handle
Returns:
The Database flags
Deprecated:
This function was replaced by ham_get_parameters and ham_env_get_parameters
HAM_EXPORT ham_status_t HAM_CALLCONV ham_get_key_count ( ham_db_t db,
ham_txn_t txn,
ham_u32_t  flags,
ham_offset_t keycount 
)

Calculates the number of keys stored in the Database

You can specify the HAM_SKIP_DUPLICATES if you do now want to include any duplicates in the count; if all you're after is a quick estimate, you can specify the flag HAM_FAST_ESTIMATE (which implies HAM_SKIP_DUPLICATES), which will improve the execution speed of this operation significantly.

Parameters:
db A valid Database handle
txn A Transaction handle, or NULL
flags Optional flags:

keycount A reference to a variable which will receive the calculated key count per page
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db or keycount is NULL or when flags contains an invalid flag set

Referenced by ham::db::get_key_count().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_get_parameters ( ham_db_t db,
ham_parameter_t param 
)

Retrieve the current value for a given Database setting

Only those values requested by the parameter array will be stored.

Parameters:
db A valid Database handle
param An array of ham_parameter_t structures
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if the db pointer is NULL or param is NULL

Referenced by ham::db::get_parameters().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_insert ( ham_db_t db,
ham_txn_t txn,
ham_key_t key,
ham_record_t record,
ham_u32_t  flags 
)

Inserts a Database item

This function inserts a key/record pair as a new Database item.

If the key already exists in the Database, error HAM_DUPLICATE_KEY is returned.

If you wish to overwrite an existing entry specify the flag HAM_OVERWRITE.

You can write only portions of the record by specifying the flag HAM_PARTIAL. In this case, hamsterdb will write partial_size bytes of the record data at offset partial_offset. The full record size will always be given in record->size! If partial_size+partial_offset exceed record->size then partial_size will be limited. To shrink or grow the record, adjust record->size. HAM_PARTIAL automatically overwrites existing records. Gaps will be filled with null-bytes if the record did not yet exist. Using HAM_PARTIAL is not allowed in combination with sorted duplicates (HAM_SORT_DUPLICATES).

If you wish to insert a duplicate key specify the flag HAM_DUPLICATE. (Note that the Database has to be created with HAM_ENABLE_DUPLICATES in order to use duplicate keys.) If no duplicate sorting is enabled (see HAM_SORT_DUPLICATES), the duplicate key is inserted after all other duplicate keys (see HAM_DUPLICATE_INSERT_LAST). Otherwise it is inserted in sorted order.

Record Number Databases (created with HAM_RECORD_NUMBER) expect either an empty key (with a size of 0 and data pointing to NULL), or a user-supplied key (with key.flag HAM_KEY_USER_ALLOC, a size of 8 and a valid data pointer). If key.size is 0 and key.data is NULL, hamsterdb will temporarily allocate memory for key->data, which will then point to an 8-byte unsigned integer in host-endian.

Parameters:
db A valid Database handle
txn A Transaction handle, or NULL
key The key of the new item
record The record of the new item
flags Optional flags for inserting. Possible flags are:

  • HAM_OVERWRITE. If the key already exists, the record is overwritten. Otherwise, the key is inserted. Flag is not allowed in combination with HAM_DUPLICATE.
  • HAM_DUPLICATE. If the key already exists, a duplicate key is inserted. The key is inserted before the already existing key, or according to the sort order. Flag is not allowed in combination with HAM_OVERWRITE.
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if db, key or record is NULL
HAM_INV_PARAMETER if the Database is a Record Number Database and the key is invalid (see above)
HAM_INV_PARAMETER if HAM_PARTIAL was specified AND duplicate sorting is enabled (HAM_SORT_DUPLICATES)
HAM_INV_PARAMETER if the flags HAM_OVERWRITE and HAM_DUPLICATE were specified, or if HAM_DUPLICATE was specified, but the Database was not created with flag HAM_ENABLE_DUPLICATES.
HAM_INV_PARAMETER if HAM_PARTIAL is specified and record->partial_offset+record->partial_size exceeds the record->size
HAM_DB_READ_ONLY if you tried to insert a key in a read-only Database
HAM_INV_KEYSIZE if the key size is larger than the keysize parameter specified for ham_create_ex and variable key sizes are disabled (see HAM_DISABLE_VAR_KEYLEN) OR if the keysize parameter specified for ham_create_ex is smaller than 8.
See also:
HAM_DISABLE_VAR_KEYLEN

Referenced by ham::db::insert().

HAM_EXPORT int HAM_CALLCONV ham_key_get_approximate_match_type ( ham_key_t key  ) 

Returns the kind of key match which produced this key as it was returned by one of the ham_find(), ham_cursor_find() or ham_cursor_find_ex() functions

This routine assumes the key was passed back by one of the ham_find, ham_cursor_find or ham_cursor_find_ex functions and not used by any other hamsterdb functions after that.

As such, this function produces an answer akin to the 'sign' of the specified key as it was returned by the find operation.

Parameters:
key A valid key
Returns:
1 (greater than) or -1 (less than) when the given key is an approximate result / zero (0) otherwise. Specifically:
  • +1 when the key is greater than the item searched for (key was a GT match)
  • -1 when the key is less than the item searched for (key was a LT match)
  • zero (0) otherwise (key was an EQ (EXACT) match)

Referenced by ham::key::get_approximate_match_type().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_set_compare_func ( ham_db_t db,
ham_compare_func_t  foo 
)

Sets the comparison function

The comparison function compares two index keys. It returns -1 if the first key is smaller, +1 if the second key is smaller or 0 if both keys are equal.

If foo is NULL, hamsterdb will use the default compare function (which is based on memcmp(3)).

Note that if you use a custom comparison routine in combination with extended keys, it might be useful to disable the prefix comparison, which is based on memcmp(3). See ham_set_prefix_compare_func for details.

Parameters:
db A valid Database handle
foo A pointer to the compare function
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if one of the parameters is NULL
See also:
ham_set_prefix_compare_func

Referenced by ham::db::set_compare_func().

HAM_EXPORT ham_status_t HAM_CALLCONV ham_set_duplicate_compare_func ( ham_db_t db,
ham_duplicate_compare_func_t  foo 
)

Sets the duplicate comparison function

The comparison function compares two records which share the same key. It returns -1 if the first record is smaller, +1 if the second record is smaller or 0 if both records are equal.

If foo is NULL, hamsterdb will use the default compare function (which is based on memcmp(3)).

To enable this function, the flag HAM_SORT_DUPLICATES has to be specified when creating or opening a Database.

Sorting duplicate keys comes with a small performance penalty compared to unsorted duplicates, since the records of other duplicates have to be fetched for the comparison.

Parameters:
db A valid Database handle
foo A pointer to the compare function
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if one of the parameters is NULL
See also:
HAM_ENABLE_DUPLICATES
HAM_SORT_DUPLICATES
HAM_EXPORT ham_status_t HAM_CALLCONV ham_set_prefix_compare_func ( ham_db_t db,
ham_prefix_compare_func_t  foo 
)

Sets the prefix comparison function

The prefix comparison function is called when an index uses keys with variable length and at least one of the two keys is loaded only partially.

If foo is NULL, hamsterdb will not use any prefix comparison.

Parameters:
db A valid Database handle
foo A pointer to the prefix compare function
Returns:
HAM_SUCCESS upon success
HAM_INV_PARAMETER if the db parameter is NULL

Referenced by ham::db::set_prefix_compare_func().


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