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<h1>DbEnv::memp_stat</h1>
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<h3><pre>
#include <db_cxx.h>
<p>
int
DbEnv::memp_stat(DB_MPOOL_STAT **gsp,
DB_MPOOL_FSTAT *(*fsp)[], u_int32_t flags);
</pre></h3>
<h1>Description</h1>
<p>The DbEnv::memp_stat and <a href="../../db4-devel-4.1.25/api_cxx/memp_stat.html">DbEnv::memp_fstat</a> methods return the memory pool
subsystem statistics.
<p>The <b>flags</b> value must be set to 0 or
the following value:
<p><dl compact>
<p><dt><a name="DB_STAT_CLEAR">DB_STAT_CLEAR</a><dd>Reset statistics after returning their values.
</dl>
<p>The DbEnv::memp_stat and <a href="../../db4-devel-4.1.25/api_cxx/memp_stat.html">DbEnv::memp_fstat</a> methods create statistical
structures of type DB_MPOOL_STAT and DB_MPOOL_FSTAT, and copy pointers
to them into user-specified memory locations. The memory pool region
statistics are stored in the DB_MPOOL_STAT structure and the per-file
memory pool statistics are stored the DB_MPOOL_FSTAT structure.
<p>Statistical structures are created in allocated memory. If application-specific allocation
routines have been declared (see <a href="../../db4-devel-4.1.25/api_cxx/env_set_alloc.html">DbEnv::set_alloc</a> for more
information), they are used to allocate the memory; otherwise, the
library <b>malloc</b>(3) interface is used. The caller is
responsible for deallocating the memory. To deallocate the memory, free
the memory reference; references inside the returned memory need not be
individually freed.
<p>If <b>gsp</b> is non-NULL, the global statistics for the memory pool
<b>mp</b> are copied into the memory location to which it refers. The
following DB_MPOOL_STAT fields will be filled in:
<p><dl compact>
<dt>size_t st_gbytes;<dd>Gigabytes of cache (total cache size is st_gbytes + st_bytes).
<dt>size_t st_bytes;<dd>Bytes of cache (total cache size is st_gbytes + st_bytes).
<dt>u_int32_t st_ncache;<dd>Number of caches.
<dt>u_int32_t st_regsize;<dd>Individual cache size.
<dt>u_int32_t st_map;<dd>Requested pages mapped into the process' address space (there is no
available information about whether or not this request caused disk I/O,
although examining the application page fault rate may be helpful).
<dt>u_int32_t st_cache_hit;<dd>Requested pages found in the cache.
<dt>u_int32_t st_cache_miss;<dd>Requested pages not found in the cache.
<dt>u_int32_t st_page_create;<dd>Pages created in the cache.
<dt>u_int32_t st_page_in;<dd>Pages read into the cache.
<dt>u_int32_t st_page_out;<dd>Pages written from the cache to the backing file.
<dt>u_int32_t st_ro_evict;<dd>Clean pages forced from the cache.
<dt>u_int32_t st_rw_evict;<dd>Dirty pages forced from the cache.
<dt>u_int32_t st_page_trickle;<dd>Dirty pages written using the <a href="../../db4-devel-4.1.25/api_cxx/memp_trickle.html">DbEnv::memp_trickle</a> interface.
<dt>u_int32_t st_pages;<dd>Pages in the cache.
<dt>u_int32_t st_page_clean;<dd>Clean pages currently in the cache.
<dt>u_int32_t st_page_dirty;<dd>Dirty pages currently in the cache.
<dt>u_int32_t st_hash_buckets;<dd>Number of hash buckets in buffer hash table.
<dt>u_int32_t st_hash_searches;<dd>Total number of buffer hash table lookups.
<dt>u_int32_t st_hash_longest;<dd>The longest chain ever encountered in buffer hash table lookups.
<dt>u_int32_t st_hash_examined;<dd>Total number of hash elements traversed during hash table lookups.
<dt>u_int32_t st_hash_nowait;<dd>The number of times that a thread of control was able to obtain a hash
bucket lock without waiting.
<dt>u_int32_t st_hash_wait;<dd>The number of times that a thread of control was forced to wait before
obtaining a hash bucket lock.
<dt>u_int32_t st_hash_max_wait;<dd>The maximum number of times any hash bucket lock was waited for by a
thread of control.
<dt>u_int32_t st_region_wait;<dd>The number of times that a thread of control was forced to wait before
obtaining a region lock.
<dt>u_int32_t st_region_nowait;<dd>The number of times that a thread of control was able to obtain a region
lock without waiting.
<dt>u_int32_t st_alloc;<dd>Number of page allocations.
<dt>u_int32_t st_alloc_buckets;<dd>Number of hash buckets checked during allocation.
<dt>u_int32_t st_alloc_max_buckets;<dd>Maximum number of hash buckets checked during an allocation.
<dt>u_int32_t st_alloc_pages;<dd>Number of pages checked during allocation.
<dt>u_int32_t st_alloc_max_pages;<dd>Maximum number of pages checked during an allocation.
</dl>
<p>If <b>fsp</b> is non-NULL, a pointer to a NULL-terminated
variable length array of statistics for individual files, in the memory
pool <b>mp</b>, is copied into the memory location to which it refers.
If no individual files currently exist in the memory pool, <b>fsp</b>
will be set to NULL.
<p>The per-file statistics are stored in structures of type DB_MPOOL_FSTAT.
The following DB_MPOOL_FSTAT fields will be filled in for each file in
the pool; that is, each element of the array:
<p><dl compact>
<dt>char *file_name;<dd>The name of the file.
<dt>size_t st_pagesize;<dd>Page size in bytes.
<dt>u_int32_t st_cache_hit;<dd>Requested pages found in the cache.
<dt>u_int32_t st_cache_miss;<dd>Requested pages not found in the cache.
<dt>u_int32_t st_map;<dd>Requested pages mapped into the process' address space.
<dt>u_int32_t st_page_create;<dd>Pages created in the cache.
<dt>u_int32_t st_page_in;<dd>Pages read into the cache.
<dt>u_int32_t st_page_out;<dd>Pages written from the cache to the backing file.
</dl>
<p>The DbEnv::memp_stat method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, and returns 0 on success.
<h1>Errors</h1>
<p>The DbEnv::memp_stat method may fail and throw an exception or return a non-zero error for the following conditions:
<p><dl compact>
<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
</dl>
<p>The DbEnv::memp_stat method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the DbEnv::memp_stat method may fail and
either return <a href="../../db4-devel-4.1.25/ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw a
<a href="../../db4-devel-4.1.25/api_cxx/runrec_class.html">DbRunRecoveryException</a>,
in which case all subsequent Berkeley DB calls will fail in the same way.
<h1>Class</h1>
<a href="../../db4-devel-4.1.25/api_cxx/env_class.html">DbEnv</a>, <a href="../../db4-devel-4.1.25/api_cxx/mempfile_class.html">DbMpoolFile</a>
<h1>See Also</h1>
<a href="../../db4-devel-4.1.25/api_cxx/memp_list.html">Memory Pools and Related Methods</a>
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