Metadata Cache

Detailed Description

Functions
herr_t	H5Fget_mdc_config (hid_t file_id, H5AC_cache_config_t *config_ptr)
	Obtains current metadata cache configuration for target file. More...
herr_t	H5Fset_mdc_config (hid_t file_id, H5AC_cache_config_t *config_ptr)
	Attempts to configure metadata cache of target file. More...
herr_t	H5Fget_mdc_hit_rate (hid_t file_id, double *hit_rate_ptr)
	Obtains target file's metadata cache hit rate. More...
herr_t	H5Fget_mdc_size (hid_t file_id, size_t *max_size_ptr, size_t *min_clean_size_ptr, size_t *cur_size_ptr, int *cur_num_entries_ptr)
	Obtains current metadata cache size data for specified file. More...
herr_t	H5Freset_mdc_hit_rate_stats (hid_t file_id)
	Resets hit rate statistics counters for the target file. More...

Function Documentation

H5Fget_mdc_config()

herr_t H5Fget_mdc_config	(	hid_t	file_id,
		H5AC_cache_config_t *	config_ptr
	)

Obtains current metadata cache configuration for target file.

Parameters

[in]	file_id	File identifier
[in,out]	config_ptr	Pointer to the H5AC_cache_config_t instance in which the current metadata cache configuration is to be reported. The fields of this structure are discussed here.

Returns

Returns a non-negative value if successful; otherwise returns a negative value.

Note

The in direction applies only to the H5AC_cache_config_t::version field. All other fields are out parameters.

H5Fget_mdc_config() loads the current metadata cache configuration into the instance of H5AC_cache_config_t pointed to by the config_ptr parameter.
The fields of the H5AC_cache_config_t structure are shown below:

typedef struct H5AC_cache_config_t {
    /* general configuration fields: */
    int version;
    hbool_t rpt_fcn_enabled;
    hbool_t open_trace_file;
    hbool_t close_trace_file;
    char trace_file_name[H5AC__MAX_TRACE_FILE_NAME_LEN + 1];
    hbool_t evictions_enabled;
    hbool_t set_initial_size;
    size_t initial_size;
    double min_clean_fraction;
    size_t max_size;
    size_t min_size;
    long int epoch_length;
 
    /* size increase control fields: */
    enum H5C_cache_incr_mode incr_mode;
    double lower_hr_threshold;
    double increment;
    hbool_t apply_max_increment;
    size_t max_increment;
    enum H5C_cache_flash_incr_mode flash_incr_mode;
    double flash_multiple;
    double flash_threshold;
 
    /* size decrease control fields: */
    enum H5C_cache_decr_mode decr_mode;
    double upper_hr_threshold;
    double decrement;
    hbool_t apply_max_decrement;
    size_t max_decrement;
    int epochs_before_eviction;
    hbool_t apply_empty_reserve;
    double empty_reserve;
 
    /* parallel configuration fields: */
    int dirty_bytes_threshold;
    int metadata_write_strategy;
} H5AC_cache_config_t;

(Click on a enumerator, field, or type for more information.)

Since

1.8.0

H5Fget_mdc_hit_rate()

herr_t H5Fget_mdc_hit_rate	(	hid_t	file_id,
		double *	hit_rate_ptr
	)

Obtains target file's metadata cache hit rate.

Parameters

[in]	file_id	File identifier
[out]	hit_rate_ptr	Pointer to the double in which the hit rate is returned. Note that hit_rate_ptr is undefined if the API call fails

Returns

Returns a non-negative value if successful; otherwise returns a negative value.

H5Fget_mdc_hit_rate() queries the metadata cache of the target file to obtain its hit rate (cache hits / (cache hits + cache misses)) since the last time hit rate statistics were reset. If the cache has not been accessed since the last time the hit rate stats were reset, the hit rate is defined to be 0.0.

The hit rate stats can be reset either manually (via H5Freset_mdc_hit_rate_stats()), or automatically. If the cache's adaptive resize code is enabled, the hit rate stats will be reset once per epoch. If they are reset manually as well, the cache may behave oddly.

See the overview of the metadata cache in the special topics section of the user manual for details on the metadata cache and its adaptive resize algorithms.

H5Fget_mdc_size()

herr_t H5Fget_mdc_size	(	hid_t	file_id,
		size_t *	max_size_ptr,
		size_t *	min_clean_size_ptr,
		size_t *	cur_size_ptr,
		int *	cur_num_entries_ptr
	)

Obtains current metadata cache size data for specified file.

Parameters

[in]	file_id	File identifier
[out]	max_size_ptr	Pointer to the location in which the current cache maximum size is to be returned, or NULL if this datum is not desired
[out]	min_clean_size_ptr	Pointer to the location in which the current cache minimum clean size is to be returned, or NULL if that datum is not desired
[out]	cur_size_ptr	Pointer to the location in which the current cache size is to be returned, or NULL if that datum is not desired
[out]	cur_num_entries_ptr	Pointer to the location in which the current number of entries in the cache is to be returned, or NULL if that datum is not desired

Returns

Returns a non-negative value if successful; otherwise returns a negative value.

H5Fget_mdc_size() queries the metadata cache of the target file for the desired size information, and returns this information in the locations indicated by the pointer parameters. If any pointer parameter is NULL, the associated data is not returned.

If the API call fails, the values returned via the pointer parameters are undefined.

If adaptive cache resizing is enabled, the cache maximum size and minimum clean size may change at the end of each epoch. Current size and current number of entries can change on each cache access.

Current size can exceed maximum size under certain conditions. See the overview of the metadata cache in the special topics section of the user manual for a discussion of this.

H5Freset_mdc_hit_rate_stats()

herr_t H5Freset_mdc_hit_rate_stats

(

hid_t

file_id

)

Resets hit rate statistics counters for the target file.

Parameters

[in]

file_id

File identifier

Returns

Returns a non-negative value if successful; otherwise returns a negative value.

H5Freset_mdc_hit_rate_stats() resets the hit rate statistics counters in the metadata cache associated with the specified file.

If the adaptive cache resizing code is enabled, the hit rate statistics are reset at the beginning of each epoch. This API call allows you to do the same thing from your program.

The adaptive cache resizing code may behave oddly if you use this call when adaptive cache resizing is enabled. However, the call should be useful if you choose to control metadata cache size from your program.

See Metadata Caching in HDF5 for details about the metadata cache and the adaptive cache resizing algorithms. If you have not read, understood, and thought about the material covered in that documentation, you should not be using this API call.

H5Fset_mdc_config()

herr_t H5Fset_mdc_config	(	hid_t	file_id,
		H5AC_cache_config_t *	config_ptr
	)

Attempts to configure metadata cache of target file.

Parameters

[in]	file_id	File identifier
[in,out]	config_ptr	Pointer to the H5AC_cache_config_t instance containing the desired configuration. The fields of this structure are discussed here.

Returns

Returns a non-negative value if successful; otherwise returns a negative value.

H5Fset_mdc_config() attempts to configure the file's metadata cache according configuration supplied in config_ptr.

typedef struct H5AC_cache_config_t {
    /* general configuration fields: */
    int version;
    hbool_t rpt_fcn_enabled;
    hbool_t open_trace_file;
    hbool_t close_trace_file;
    char trace_file_name[H5AC__MAX_TRACE_FILE_NAME_LEN + 1];
    hbool_t evictions_enabled;
    hbool_t set_initial_size;
    size_t initial_size;
    double min_clean_fraction;
    size_t max_size;
    size_t min_size;
    long int epoch_length;
 
    /* size increase control fields: */
    enum H5C_cache_incr_mode incr_mode;
    double lower_hr_threshold;
    double increment;
    hbool_t apply_max_increment;
    size_t max_increment;
    enum H5C_cache_flash_incr_mode flash_incr_mode;
    double flash_multiple;
    double flash_threshold;
 
    /* size decrease control fields: */
    enum H5C_cache_decr_mode decr_mode;
    double upper_hr_threshold;
    double decrement;
    hbool_t apply_max_decrement;
    size_t max_decrement;
    int epochs_before_eviction;
    hbool_t apply_empty_reserve;
    double empty_reserve;
 
    /* parallel configuration fields: */
    int dirty_bytes_threshold;
    int metadata_write_strategy;
} H5AC_cache_config_t;

(Click on a enumerator, field, or type for more information.)

Since

1.8.0