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<h3>DB_ENV->memp_stat</h3>
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<h3><pre>
#include <db.h>
<p>
int
DB_ENV->memp_stat(DB_ENV *env, DB_MPOOL_STAT **gsp,
DB_MPOOL_FSTAT *(*fsp)[], u_int32_t flags);
</pre></h3>
<hr size=1 noshade>
<h3>Description: DB_ENV->memp_stat</h3>
<p>The DB_ENV->memp_stat method returns the memory pool (that is, the buffer
cache) subsystem statistics.</p>
<p>The DB_ENV->memp_stat method creates statistical structures of type DB_MPOOL_STAT
and DB_MPOOL_FSTAT, and copy pointers to them into user-specified memory
locations. The cache statistics are stored in the DB_MPOOL_STAT structure
and the per-file cache statistics are stored the DB_MPOOL_FSTAT structure.</p>
<p>Statistical structures are stored in allocated memory. If application-specific allocation
routines have been declared (see <a href="../../db42-devel-4.2.52/api_c/env_set_alloc.html">DB_ENV->set_alloc</a> for more
information), they are used to allocate the memory; otherwise, the
standard C library <b>malloc</b>(3) 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>
<p>If <b>gsp</b> is non-NULL, the global statistics for the cache
<b>mp</b> are copied into the memory location to which it refers.
The following DB_MPOOL_STAT fields will be filled in:</p>
<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="../../db42-devel-4.2.52/api_c/memp_trickle.html">DB_ENV->memp_trickle</a> method.
<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 cache
<b>mp</b>, is copied into the memory location to which it refers. If
no individual files currently exist in the cache, <b>fsp</b> will be
set to NULL.</p>
<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 cache; that is, each element of the array:</p>
<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 DB_ENV->memp_stat method
returns a non-zero error value on failure
and 0 on success.
</p>
<h3>Parameters</h3>
<p><dl compact>
<p><dt><b>flags</b><dd>
The <b>flags</b> parameter 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><dt><b>fsp</b><dd>
The <b>fsp</b> parameter references memory into which
a pointer to the allocated per-file statistics structures is copied.
<p><dt><b>gsp</b><dd>
The <b>gsp</b> parameter references memory into which
a pointer to the allocated global statistics structure is copied.
</dl>
<h3>Errors</h3>
<p>The DB_ENV->memp_stat method
may fail and return one of the following non-zero errors:</p>
<p><dl compact>
<p><dt>EINVAL<dd>An
invalid flag value or parameter was specified.
</dl>
<hr size=1 noshade>
<h3>Class</h3>
<a href="../../db42-devel-4.2.52/api_c/env_class.html">DB_ENV</a>, <a href="../../db42-devel-4.2.52/api_c/mempfile_class.html">DB_MPOOLFILE</a>
<h3>See Also</h3>
<a href="../../db42-devel-4.2.52/api_c/memp_list.html">Memory Pools and Related Methods</a>
</tt>
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