H5ACpkg.h

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
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/*
 * Programmer: John Mainzer -- 4/19/06
 *
 * Purpose:     This file contains declarations which are normally visible
 *              only within the H5AC package (just H5AC.c at present).
 *
 *              Source files outside the H5AC package should include
 *              H5ACprivate.h instead.
 *
 *              The one exception to this rule is testpar/t_cache.c.  The
 *              test code is easier to write if it can look at H5AC_aux_t.
 *              Indeed, this is the main reason why this file was created.
 */

#ifndef H5AC_PACKAGE
#error "Do not include this file outside the H5AC package!"
#endif

#ifndef _H5ACpkg_H
#define _H5ACpkg_H

/* Get package's private header */
#include "H5ACprivate.h"


/* Get needed headers */
#include "H5Cprivate.h"         /* Cache                                */
#include "H5SLprivate.h"        /* Skip lists */


#define H5AC_DEBUG_DIRTY_BYTES_CREATION 0

/*-------------------------------------------------------------------------
 *  It is a bit difficult to set ranges of allowable values on the
 *  dirty_bytes_threshold field of H5AC_aux_t.  The following are
 *  probably broader than they should be.
 *-------------------------------------------------------------------------
 */

#define H5AC__MIN_DIRTY_BYTES_THRESHOLD         (int32_t) \
                                                (H5C__MIN_MAX_CACHE_SIZE / 2)
#define H5AC__DEFAULT_DIRTY_BYTES_THRESHOLD     (256 * 1024)
#define H5AC__MAX_DIRTY_BYTES_THRESHOLD         (int32_t) \
                                                (H5C__MAX_MAX_CACHE_SIZE / 4)

/****************************************************************************
 *
 * structure H5AC_aux_t
 *
 * While H5AC has become a wrapper for the cache implemented in H5C.c, there
 * are some features of the metadata cache that are specific to it, and which
 * therefore do not belong in the more generic H5C cache code.
 *
 * In particular, there is the matter of synchronizing writes from the
 * metadata cache to disk in the PHDF5 case.
 *
 * Prior to this update, the presumption was that all metadata caches would
 * write the same data at the same time since all operations modifying
 * metadata must be performed collectively.  Given this assumption, it was
 * safe to allow only the writes from process 0 to actually make it to disk,
 * while metadata writes from all other processes were discarded.
 *
 * Unfortunately, this presumption is in error as operations that read
 * metadata need not be collective, but can change the location of dirty
 * entries in the metadata cache LRU lists.  This can result in the same
 * metadata write operation triggering writes from the metadata caches on
 * some processes, but not all (causing a hang), or in different sets of
 * entries being written from different caches (potentially resulting in
 * metadata corruption in the file).
 *
 * To deal with this issue, I decided to apply a paradigm shift to the way
 * metadata is written to disk.
 *
 * With this set of changes, only the metadata cache on process 0 is able
 * to write metadata to disk, although metadata caches on all other
 * processes can read metadata from disk as before.
 *
 * To keep all the other caches from getting plugged up with dirty metadata,
 * process 0 periodically broadcasts a list of entries that it has flushed
 * since that last notice, and which are currently clean.  The other caches
 * mark these entries as clean as well, which allows them to evict the
 * entries as needed.
 *
 * One obvious problem in this approach is synchronizing the broadcasts
 * and receptions, as different caches may see different amounts of
 * activity.
 *
 * The current solution is for the caches to track the number of bytes
 * of newly generated dirty metadata, and to broadcast and receive
 * whenever this value exceeds some user specified threshold.
 *
 * Maintaining this count is easy for all processes not on process 0 --
 * all that is necessary is to add the size of the entry to the total
 * whenever there is an insertion, a rename of a previously clean entry,
 * or whever a previously clean entry is marked dirty in an unprotect.
 *
 * On process 0, we have to be careful not to count dirty bytes twice.
 * If an entry is marked dirty, flushed, and marked dirty again, all
 * within a single reporting period, it only th first marking should
 * be added to the dirty bytes generated tally, as that is all that
 * the other processes will see.
 *
 * At present, this structure exists to maintain the fields needed to
 * implement the above scheme, and thus is only used in the parallel
 * case.  However, other uses may arise in the future.
 *
 * Instance of this structure are associated with metadata caches via
 * the aux_ptr field of H5C_t (see H5Cpkg.h).  The H5AC code is
 * responsible for allocating, maintaining, and discarding instances
 * of H5AC_aux_t.
 *
 * The remainder of this header comments documents the individual fields
 * of the structure.
 *
 *                                              JRM - 6/27/05
 *
 * magic:       Unsigned 32 bit integer always set to
 *              H5AC__H5AC_AUX_T_MAGIC.  This field is used to validate
 *              pointers to instances of H5AC_aux_t.
 *
 * mpi_comm:    MPI communicator associated with the file for which the
 *              cache has been created.
 *
 * mpi_rank:    MPI rank of this process within mpi_comm.
 *
 * mpi_size:    Number of processes in mpi_comm.
 *
 * write_permitted:  Boolean flag used to control whether the cache
 *              is permitted to write to file.
 *
 * dirty_bytes_threshold: Integer field containing the dirty bytes
 *              generation threashold.  Whenever dirty byte creation
 *              exceeds this value, the metadata cache on process 0
 *              broadcasts a list of the entries it has flushed since
 *              the last broadcast (or since the beginning of execution)
 *              and which are currently clean (if they are still in the
 *              cache)
 *
 *              Similarly, metadata caches on processes other than process
 *              0 will attempt to receive a list of clean entries whenever
 *              the threshold is exceeded.
 *
 * dirty_bytes:  Integer field containing the number of bytes of dirty
 *              metadata generated since the beginning of the computation,
 *              or (more typically) since the last clean entries list
 *              broadcast.  This field is reset to zero after each such
 *              broadcast.
 *
 * dirty_bytes_propagations: This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of times the cleaned list
 *              has been propagated from process 0 to the other
 *              processes.
 *
 * unprotect_dirty_bytes:  This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of dirty bytes created
 *              via unprotect operations since the last time the cleaned
 *              list was propagated.
 *
 * unprotect_dirty_bytes_updates: This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of times dirty bytes have
 *              been created via unprotect operations since the last time
 *              the cleaned list was propagated.
 *
 * insert_dirty_bytes:  This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of dirty bytes created
 *              via insert operations since the last time the cleaned
 *              list was propagated.
 *
 * insert_dirty_bytes_updates:  This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of times dirty bytes have
 *              been created via insert operations since the last time
 *              the cleaned list was propagated.
 *
 * rename_dirty_bytes:  This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of dirty bytes created
 *              via rename operations since the last time the cleaned
 *              list was propagated.
 *
 * rename_dirty_bytes_updates:  This field only exists when the
 *              H5AC_DEBUG_DIRTY_BYTES_CREATION #define is TRUE.
 *
 *              It is used to track the number of times dirty bytes have
 *              been created via rename operations since the last time
 *              the cleaned list was propagated.
 *
 * d_slist_ptr:  Pointer to an instance of H5SL_t used to maintain a list
 *              of entries that have been dirtied since the last time they
 *              were listed in a clean entries broadcast.  This list is
 *              only maintained by the metadata cache on process 0 -- it
 *              it used to maintain a view of the dirty entries as seen
 *              by the other caches, so as to keep the dirty bytes count
 *              in synchronization with them.
 *
 *              Thus on process 0, the dirty_bytes count is incremented
 *              only if either
 *
 *              1) an entry is inserted in the metadata cache, or
 *
 *              2) a previously clean entry is renamed, and it does not
 *                 already appear in the dirty entry list, or
 *
 *              3) a previously clean entry is unprotected with the
 *                 dirtied flag set and the entry does not already appear
 *                 in the dirty entry list.
 *
 *              Entries are added to the dirty entry list whever they cause
 *              the dirty bytes count to be increased.  They are removed
 *              when they appear in a clean entries broadcast.  Note that
 *              renames must be reflected in the dirty entry list.
 *
 *              To reitterate, this field is only used on process 0 -- it
 *              should be NULL on all other processes.
 *
 * d_slist_len: Integer field containing the number of entries in the
 *              dirty entry list.  This field should always contain the
 *              value 0 on all processes other than process 0.  It exists
 *              primarily for sanity checking.
 *
 * c_slist_ptr: Pointer to an instance of H5SL_t used to maintain a list
 *              of entries that were dirty, have been flushed
 *              to disk since the last clean entries broadcast, and are
 *              still clean.  Since only process 0 can write to disk, this
 *              list only exists on process 0.
 *
 *              In essence, this slist is used to assemble the contents of
 *              the next clean entries broadcast.  The list emptied after
 *              each broadcast.
 *
 * c_slist_len: Integer field containing the number of entries in the clean
 *              entries list (*c_slist_ptr).  This field should always
 *              contain the value 0 on all processes other than process 0.
 *              It exists primarily for sanity checking.
 *
 * write_done:  In the parallel test bed, it is necessary to ensure that
 *              all writes to the server process from cache 0 complete
 *              before it enters the barrier call with the other caches.
 *
 *              The write_done callback allows t_cache to do this without
 *              requiring an ACK on each write.  Since these ACKs greatly
 *              increase the run time on some platforms, this is a
 *              significant optimization.
 *
 *              This field must be set to NULL when the callback is not
 *              needed.
 *
 ****************************************************************************/

#ifdef H5_HAVE_PARALLEL

#define H5AC__H5AC_AUX_T_MAGIC        (unsigned)0x00D0A01

typedef struct H5AC_aux_t
{
    uint32_t    magic;

    MPI_Comm    mpi_comm;

    int         mpi_rank;

    int         mpi_size;

    hbool_t     write_permitted;

    int32_t     dirty_bytes_threshold;

    int32_t     dirty_bytes;

#if H5AC_DEBUG_DIRTY_BYTES_CREATION

    int32_t     dirty_bytes_propagations;

    int32_t     unprotect_dirty_bytes;
    int32_t     unprotect_dirty_bytes_updates;

    int32_t     insert_dirty_bytes;
    int32_t     insert_dirty_bytes_updates;

    int32_t     rename_dirty_bytes;
    int32_t     rename_dirty_bytes_updates;

#endif /* H5AC_DEBUG_DIRTY_BYTES_CREATION */

    H5SL_t *    d_slist_ptr;

    int32_t     d_slist_len;

    H5SL_t *    c_slist_ptr;

    int32_t     c_slist_len;

    void        (* write_done)(void);

} H5AC_aux_t; /* struct H5AC_aux_t */

#endif /* H5_HAVE_PARALLEL */

#endif /* _H5ACpkg_H */