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* Copyright by The HDF Group. *
* Copyright by the Board of Trustees of the University of Illinois. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the files COPYING and Copyright.html. COPYING can be found at the root *
* of the source code distribution tree; Copyright.html can be found at the *
* root level of an installed copy of the electronic HDF5 document set and *
* is linked from the top-level documents page. It can also be found at *
* http://hdfgroup.org/HDF5/doc/Copyright.html. If you do not have *
* access to either file, you may request a copy from help@hdfgroup.org. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*-------------------------------------------------------------------------
*
* Created: H5ACpublic.h
* Jul 10 1997
* Robb Matzke <matzke@llnl.gov>
*
* Purpose: Public include file for cache functions.
*
* Modifications:
*
*-------------------------------------------------------------------------
*/
#ifndef _H5ACpublic_H
#define _H5ACpublic_H
/* Public headers needed by this file */
#include "H5public.h"
#include "H5Cpublic.h"
#ifdef __cplusplus
extern "C" {
#endif
/****************************************************************************
*
* structure H5AC_cache_config_t
*
* H5AC_cache_config_t is a public structure intended for use in public APIs.
* At least in its initial incarnation, it is basicaly a copy of struct
* H5C_auto_size_ctl_t, minus the report_fcn field, and plus the
* dirty_bytes_threshold field.
*
* The report_fcn field is omitted, as including it would require us to
* make H5C_t structure public.
*
* The dirty_bytes_threshold field does not appear in H5C_auto_size_ctl_t,
* as synchronization between caches on different processes is handled at
* the H5AC level, not at the level of H5C. Note however that there is
* considerable interaction between this value and the other fields in this
* structure.
*
* Similarly, the open_trace_file, close_trace_file, and trace_file_name
* fields do not appear in H5C_auto_size_ctl_t, as most trace file
* issues are handled at the H5AC level. The one exception is storage of
* the pointer to the trace file, which is handled by H5C.
*
* The structure is in H5ACpublic.h as we may wish to allow different
* configuration options for metadata and raw data caches.
*
* The fields of the structure are discussed individually below:
*
* version: Integer field containing the version number of this version
* of the H5AC_cache_config_t structure. Any instance of
* H5AC_cache_config_t passed to the cache must have a known
* version number, or an error will be flagged.
*
* rpt_fcn_enabled: Boolean field used to enable and disable the default
* reporting function. This function is invoked every time the
* automatic cache resize code is run, and reports on its activities.
*
* This is a debugging function, and should normally be turned off.
*
* open_trace_file: Boolean field indicating whether the trace_file_name
* field should be used to open a trace file for the cache.
*
* The trace file is a debuging feature that allow the capture of
* top level metadata cache requests for purposes of debugging and/or
* optimization. This field should normally be set to FALSE, as
* trace file collection imposes considerable overhead.
*
* This field should only be set to TRUE when the trace_file_name
* contains the full path of the desired trace file, and either
* there is no open trace file on the cache, or the close_trace_file
* field is also TRUE.
*
* close_trace_file: Boolean field indicating whether the current trace
* file (if any) should be closed.
*
* See the above comments on the open_trace_file field. This field
* should be set to FALSE unless there is an open trace file on the
* cache that you wish to close.
*
* trace_file_name: Full path of the trace file to be opened if the
* open_trace_file field is TRUE.
*
* In the parallel case, an ascii representation of the mpi rank of
* the process will be appended to the file name to yield a unique
* trace file name for each process.
*
* The length of the path must not exceed H5AC__MAX_TRACE_FILE_NAME_LEN
* characters.
*
* evictions_enabled: Boolean field used to either report the current
* evictions enabled status of the cache, or to set the cache's
* evictions enabled status.
*
* In general, the metadata cache should always be allowed to
* evict entries. However, in some cases it is advantageous to
* disable evictions briefly, and thereby postpone metadata
* writes. However, this must be done with care, as the cache
* can grow quickly. If you do this, re-enable evictions as
* soon as possible and monitor cache size.
*
* At present, evictions can only be disabled if automatic
* cache resizing is also disabled (that is, ( incr_mode ==
* H5C_incr__off ) && ( decr_mode == H5C_decr__off )). There
* is no logical reason why this should be so, but it simplifies
* implementation and testing, and I can't think of any reason
* why it would be desireable. If you can think of one, I'll
* revisit the issue.
*
* set_initial_size: Boolean flag indicating whether the size of the
* initial size of the cache is to be set to the value given in
* the initial_size field. If set_initial_size is FALSE, the
* initial_size field is ignored.
*
* initial_size: If enabled, this field contain the size the cache is
* to be set to upon receipt of this structure. Needless to say,
* initial_size must lie in the closed interval [min_size, max_size].
*
* min_clean_fraction: double in the range 0 to 1 indicating the fraction
* of the cache that is to be kept clean. This field is only used
* in parallel mode. Typical values are 0.1 to 0.5.
*
* max_size: Maximum size to which the cache can be adjusted. The
* supplied value must fall in the closed interval
* [MIN_MAX_CACHE_SIZE, MAX_MAX_CACHE_SIZE]. Also, max_size must
* be greater than or equal to min_size.
*
* min_size: Minimum size to which the cache can be adjusted. The
* supplied value must fall in the closed interval
* [H5C__MIN_MAX_CACHE_SIZE, H5C__MAX_MAX_CACHE_SIZE]. Also, min_size
* must be less than or equal to max_size.
*
* epoch_length: Number of accesses on the cache over which to collect
* hit rate stats before running the automatic cache resize code,
* if it is enabled.
*
* At the end of an epoch, we discard prior hit rate data and start
* collecting afresh. The epoch_length must lie in the closed
* interval [H5C__MIN_AR_EPOCH_LENGTH, H5C__MAX_AR_EPOCH_LENGTH].
*
*
* Cache size increase control fields:
*
* incr_mode: Instance of the H5C_cache_incr_mode enumerated type whose
* value indicates how we determine whether the cache size should be
* increased. At present there are two possible values:
*
* H5C_incr__off: Don't attempt to increase the size of the cache
* automatically.
*
* When this increment mode is selected, the remaining fields
* in the cache size increase section ar ignored.
*
* H5C_incr__threshold: Attempt to increase the size of the cache
* whenever the average hit rate over the last epoch drops
* below the value supplied in the lower_hr_threshold
* field.
*
* Note that this attempt will fail if the cache is already
* at its maximum size, or if the cache is not already using
* all available space.
*
* Note that you must set decr_mode to H5C_incr__off if you
* disable metadata cache entry evictions.
*
* lower_hr_threshold: Lower hit rate threshold. If the increment mode
* (incr_mode) is H5C_incr__threshold and the hit rate drops below the
* value supplied in this field in an epoch, increment the cache size by
* size_increment. Note that cache size may not be incremented above
* max_size, and that the increment may be further restricted by the
* max_increment field if it is enabled.
*
* When enabled, this field must contain a value in the range [0.0, 1.0].
* Depending on the incr_mode selected, it may also have to be less than
* upper_hr_threshold.
*
* increment: Double containing the multiplier used to derive the new
* cache size from the old if a cache size increment is triggered.
* The increment must be greater than 1.0, and should not exceed 2.0.
*
* The new cache size is obtained my multiplying the current max cache
* size by the increment, and then clamping to max_size and to stay
* within the max_increment as necessary.
*
* apply_max_increment: Boolean flag indicating whether the max_increment
* field should be used to limit the maximum cache size increment.
*
* max_increment: If enabled by the apply_max_increment field described
* above, this field contains the maximum number of bytes by which the
* cache size can be increased in a single re-size.
*
* flash_incr_mode: Instance of the H5C_cache_flash_incr_mode enumerated
* type whose value indicates whether and by which algorithm we should
* make flash increases in the size of the cache to accomodate insertion
* of large entries and large increases in the size of a single entry.
*
* The addition of the flash increment mode was occasioned by performance
* problems that appear when a local heap is increased to a size in excess
* of the current cache size. While the existing re-size code dealt with
* this eventually, performance was very bad for the remainder of the
* epoch.
*
* At present, there are two possible values for the flash_incr_mode:
*
* H5C_flash_incr__off: Don't perform flash increases in the size of
* the cache.
*
* H5C_flash_incr__add_space: Let x be either the size of a newly
* newly inserted entry, or the number of bytes by which the
* size of an existing entry has been increased.
*
* If
* x > flash_threshold * current max cache size,
*
* increase the current maximum cache size by x * flash_multiple
* less any free space in the cache, and star a new epoch. For
* now at least, pay no attention to the maximum increment.
*
* In both of the above cases, the flash increment pays no attention to
* the maximum increment (at least in this first incarnation), but DOES
* stay within max_size.
*
* With a little thought, it should be obvious that the above flash
* cache size increase algorithm is not sufficient for all circumstances
* -- for example, suppose the user round robins through
* (1/flash_threshold) +1 groups, adding one data set to each on each
* pass. Then all will increase in size at about the same time, requiring
* the max cache size to at least double to maintain acceptable
* performance, however the above flash increment algorithm will not be
* triggered.
*
* Hopefully, the add space algorithms detailed above will be sufficient
* for the performance problems encountered to date. However, we should
* expect to revisit the issue.
*
* flash_multiple: Double containing the multiple described above in the
* H5C_flash_incr__add_space section of the discussion of the
* flash_incr_mode section. This field is ignored unless flash_incr_mode
* is H5C_flash_incr__add_space.
*
* flash_threshold: Double containing the factor by which current max cache
* size is multiplied to obtain the size threshold for the add_space flash
* increment algorithm. The field is ignored unless flash_incr_mode is
* H5C_flash_incr__add_space.
*
*
* Cache size decrease control fields:
*
* decr_mode: Instance of the H5C_cache_decr_mode enumerated type whose
* value indicates how we determine whether the cache size should be
* decreased. At present there are four possibilities.
*
* H5C_decr__off: Don't attempt to decrease the size of the cache
* automatically.
*
* When this increment mode is selected, the remaining fields
* in the cache size decrease section are ignored.
*
* H5C_decr__threshold: Attempt to decrease the size of the cache
* whenever the average hit rate over the last epoch rises
* above the value supplied in the upper_hr_threshold
* field.
*
* H5C_decr__age_out: At the end of each epoch, search the cache for
* entries that have not been accessed for at least the number
* of epochs specified in the epochs_before_eviction field, and
* evict these entries. Conceptually, the maximum cache size
* is then decreased to match the new actual cache size. However,
* this reduction may be modified by the min_size, the
* max_decrement, and/or the empty_reserve.
*
* H5C_decr__age_out_with_threshold: Same as age_out, but we only
* attempt to reduce the cache size when the hit rate observed
* over the last epoch exceeds the value provided in the
* upper_hr_threshold field.
*
* Note that you must set decr_mode to H5C_decr__off if you
* disable metadata cache entry evictions.
*
* upper_hr_threshold: Upper hit rate threshold. The use of this field
* varies according to the current decr_mode:
*
* H5C_decr__off or H5C_decr__age_out: The value of this field is
* ignored.
*
* H5C_decr__threshold: If the hit rate exceeds this threshold in any
* epoch, attempt to decrement the cache size by size_decrement.
*
* Note that cache size may not be decremented below min_size.
*
* Note also that if the upper_threshold is 1.0, the cache size
* will never be reduced.
*
* H5C_decr__age_out_with_threshold: If the hit rate exceeds this
* threshold in any epoch, attempt to reduce the cache size
* by evicting entries that have not been accessed for more
* than the specified number of epochs.
*
* decrement: This field is only used when the decr_mode is
* H5C_decr__threshold.
*
* The field is a double containing the multiplier used to derive the
* new cache size from the old if a cache size decrement is triggered.
* The decrement must be in the range 0.0 (in which case the cache will
* try to contract to its minimum size) to 1.0 (in which case the
* cache will never shrink).
*
* apply_max_decrement: Boolean flag used to determine whether decrements
* in cache size are to be limited by the max_decrement field.
*
* max_decrement: Maximum number of bytes by which the cache size can be
* decreased in a single re-size. Note that decrements may also be
* restricted by the min_size of the cache, and (in age out modes) by
* the empty_reserve field.
*
* epochs_before_eviction: Integer field used in H5C_decr__age_out and
* H5C_decr__age_out_with_threshold decrement modes.
*
* This field contains the number of epochs an entry must remain
* unaccessed before it is evicted in an attempt to reduce the
* cache size. If applicable, this field must lie in the range
* [1, H5C__MAX_EPOCH_MARKERS].
*
* apply_empty_reserve: Boolean field controlling whether the empty_reserve
* field is to be used in computing the new cache size when the
* decr_mode is H5C_decr__age_out or H5C_decr__age_out_with_threshold.
*
* empty_reserve: To avoid a constant racheting down of cache size by small
* amounts in the H5C_decr__age_out and H5C_decr__age_out_with_threshold
* modes, this field allows one to require that any cache size
* reductions leave the specified fraction of unused space in the cache.
*
* The value of this field must be in the range [0.0, 1.0]. I would
* expect typical values to be in the range of 0.01 to 0.1.
*
*
* Parallel Configuration Fields:
*
* In PHDF5, all operations that modify metadata must be executed collectively.
*
* We used to think that this was enough to ensure consistency across the
* metadata caches, but since we allow processes to read metadata individually,
* the order of dirty entries in the LRU list can vary across processes,
* which can result in inconsistencies between the caches.
*
* PHDF5 uses several strategies to prevent such inconsistencies in metadata,
* all of which use the fact that the same stream of dirty metadata is seen
* by all processes for purposes of synchronization. This is done by
* having each process count the number of bytes of dirty metadata generated,
* and then running a "sync point" whenever this count exceeds a user
* specified threshold (see dirty_bytes_threshold below).
*
* The current metadata write strategy is indicated by the
* metadata_write_strategy field. The possible values of this field, along
* with the associated metadata write strategies are discussed below.
*
* dirty_bytes_threshold: Threshold of dirty byte creation used to
* synchronize updates between caches. (See above for outline and
* motivation.)
*
* This value MUST be consistant across all processes accessing the
* file. This field is ignored unless HDF5 has been compiled for
* parallel.
*
* metadata_write_strategy: Integer field containing a code indicating the
* desired metadata write strategy. The valid values of this field
* are enumerated and discussed below:
*
*
* H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY:
*
* When metadata_write_strategy is set to this value, only process
* zero is allowed to write dirty metadata to disk. All other
* processes must retain dirty metadata until they are informed at
* a sync point that the dirty metadata in question has been written
* to disk.
*
* When the sync point is reached (or when there is a user generated
* flush), process zero flushes sufficient entries to bring it into
* complience with its min clean size (or flushes all dirty entries in
* the case of a user generated flush), broad casts the list of
* entries just cleaned to all the other processes, and then exits
* the sync point.
*
* Upon receipt of the broadcast, the other processes mark the indicated
* entries as clean, and leave the sync point as well.
*
*
* H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED:
*
* In the distributed metadata write strategy, process zero still makes
* the decisions as to what entries should be flushed, but the actual
* flushes are distributed across the processes in the computation to
* the extent possible.
*
* In this strategy, when a sync point is triggered (either by dirty
* metadata creation or manual flush), all processes enter a barrier.
*
* On the other side of the barrier, process 0 constructs an ordered
* list of the entries to be flushed, and then broadcasts this list
* to the caches in all the processes.
*
* All processes then scan the list of entries to be flushed, flushing
* some, and marking the rest as clean. The algorithm for this purpose
* ensures that each entry in the list is flushed exactly once, and
* all are marked clean in each cache.
*
* Note that in the case of a flush of the cache, no message passing
* is necessary, as all processes have the same list of dirty entries,
* and all of these entries must be flushed. Thus in this case it is
* sufficient for each process to sort its list of dirty entries after
* leaving the initial barrier, and use this list as if it had been
* received from process zero.
*
* To avoid possible messages from the past/future, all caches must
* wait until all caches are done before leaving the sync point.
*
****************************************************************************/
#define H5AC__CURR_CACHE_CONFIG_VERSION 1
#define H5AC__MAX_TRACE_FILE_NAME_LEN 1024
#define H5AC_METADATA_WRITE_STRATEGY__PROCESS_0_ONLY 0
#define H5AC_METADATA_WRITE_STRATEGY__DISTRIBUTED 1
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;
#ifdef __cplusplus
}
#endif
#endif
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