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<h2 class="title" style="clear: both"><a id="mempstat"></a>DbEnv::memp_stat()</h2>
</div>
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<pre class="programlisting">#include <db_cxx.h>
int
DbEnv::memp_stat(DB_MPOOL_STAT **gsp,
DB_MPOOL_FSTAT *(*fsp)[], u_int32_t flags); </pre>
<p>
The <code class="methodname">DbEnv::memp_stat()</code> method returns the memory pool (that is, the
buffer cache) subsystem statistics.
</p>
<p>
The <code class="methodname">DbEnv::memp_stat()</code> method creates statistical structures of
type <code class="literal">DB_MPOOL_STAT</code> and <code class="literal">DB_MPOOL_FSTAT</code>, and copy
pointers to them into user-specified memory locations. The cache statistics are stored in
the <code class="literal">DB_MPOOL_STAT</code> structure and the per-file cache statistics are stored
the <code class="literal">DB_MPOOL_FSTAT</code> structure.
</p>
<p>
Statistical structures are stored in allocated memory. If
application-specific allocation routines have been declared (see
<a class="xref" href="envset_alloc.html" title="DbEnv::set_alloc()">DbEnv::set_alloc()</a>
for more information), they are used to allocate the memory;
otherwise, the standard C library <span class="bold"><strong>malloc</strong></span>(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 <span class="bold"><strong>gsp</strong></span> is non-NULL, the global
statistics for the cache <span class="bold"><strong>mp</strong></span> are
copied into the memory location to which it refers. The following
<code class="literal">DB_MPOOL_STAT</code> fields will be filled in:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>u_int32_t st_gbytes;</strong></span>
</p>
<p>
Gigabytes of cache (total cache size is st_gbytes + st_bytes).
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_bytes;</strong></span>
</p>
<p>
Bytes of cache (total cache size is st_gbytes + st_bytes).
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_ncache;</strong></span>
</p>
<p>
Number of caches.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_max_ncache;</strong></span>
</p>
<p>
Maximum number of caches, as configured with the
<a class="xref" href="envset_cache_max.html" title="DbEnv::set_cache_max()">DbEnv::set_cache_max()</a>
method.
</p>
</li>
<li>
<p>
<span class="bold"><strong>roff_t st_regsize;</strong></span>
</p>
<p>
Individual cache size, in bytes.
</p>
</li>
<li>
<p>
<span class="bold"><strong>size_t st_mmapsize;</strong></span>
</p>
<p>
Maximum memory-mapped file size.
</p>
</li>
<li>
<p>
<span class="bold"><strong>int st_maxopenfd;</strong></span>
</p>
<p>
Maximum open file descriptors.
</p>
</li>
<li>
<p>
<span class="bold"><strong>int st_maxwrite;</strong></span>
</p>
<p>
Maximum sequential buffer writes.
</p>
</li>
<li>
<p>
<span class="bold"><strong>db_timeout_t st_maxwrite_sleep;</strong></span>
</p>
<p>
Microseconds to pause after writing maximum sequential buffers.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_map;</strong></span>
</p>
<p>
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).
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_cache_hit;</strong></span>
</p>
<p>
Requested pages found in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_cache_miss;</strong></span>
</p>
<p>
Requested pages not found in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_create;</strong></span>
</p>
<p>
Pages created in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_in;</strong></span>
</p>
<p>
Pages read into the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_out;</strong></span>
</p>
<p>
Pages written from the cache to the backing file.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_ro_evict;</strong></span>
</p>
<p>
Clean pages forced from the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_rw_evict;</strong></span>
</p>
<p>
Dirty pages forced from the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_trickle;</strong></span>
</p>
<p>
Dirty pages written using the
<a class="xref" href="memptrickle.html" title="DbEnv::memp_trickle()">DbEnv::memp_trickle()</a>
method.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_pages;</strong></span>
</p>
<p>
Pages in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_page_clean;</strong></span>
</p>
<p>
Clean pages currently in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_page_dirty;</strong></span>
</p>
<p>
Dirty pages currently in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_hash_buckets;</strong></span>
</p>
<p>
Number of hash buckets in buffer hash table.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_hash_examined;</strong></span>
</p>
<p>
Total number of hash elements traversed during hash table lookups.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_hash_longest;</strong></span>
</p>
<p>
Longest chain ever encountered in buffer hash table lookups.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_hash_mutexes;</strong></span>
</p>
<p>
The number of hash bucket mutexes in the buffer hash table.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_hash_nowait;</strong></span>
</p>
<p>
Number of times that a thread of control was able to obtain a hash
bucket lock without waiting.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_hash_searches;</strong></span>
</p>
<p>
Total number of buffer hash table lookups.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_hash_wait;</strong></span>
</p>
<p>
Number of times that a thread of control was forced to wait before
obtaining a hash bucket lock.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_hash_max_nowait;</strong></span>
</p>
<p>
The number of times a thread of control was able to obtain the hash
bucket lock without waiting on the bucket which had the maximum number
of times that a thread of control needed to wait.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_hash_max_wait;</strong></span>
</p>
<p>
Maximum number of times any hash bucket lock was waited for by a
thread of control.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_region_wait;</strong></span>
</p>
<p>
Number of times that a thread of control was forced to wait before
obtaining a cache region mutex.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_region_nowait;</strong></span>
</p>
<p>
Number of times that a thread of control was able to obtain a cache
region mutex without waiting.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_mvcc_frozen;</strong></span>
</p>
<p>
Number of buffers frozen.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_mvcc_thawed;</strong></span>
</p>
<p>
Number of buffers thawed.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_mvcc_freed;</strong></span>
</p>
<p>
Number of frozen buffers freed.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_alloc;</strong></span>
</p>
<p>
Number of page allocations.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_alloc_buckets;</strong></span>
</p>
<p>
Number of hash buckets checked during allocation.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_alloc_max_buckets;</strong></span>
</p>
<p>
Maximum number of hash buckets checked during an allocation.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_alloc_pages;</strong></span>
</p>
<p>
Number of pages checked during allocation.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_alloc_max_pages;</strong></span>
</p>
<p>
Maximum number of pages checked during an allocation.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_io_wait;</strong></span>
</p>
<p>
Number of operations blocked waiting for I/O to complete.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_sync_interrupted;</strong></span>
</p>
<p>
Number of mpool sync operations interrupted.
</p>
</li>
</ul>
</div>
<p>
If <span class="bold"><strong>fsp</strong></span> is non-NULL, a pointer to a
NULL-terminated variable length array of statistics for individual
files, in the cache <span class="bold"><strong>mp</strong></span>, is copied
into the memory location to which it refers. If no individual files
currently exist in the cache, <span class="bold"><strong>fsp</strong></span>
will be set to NULL.
</p>
<p>
The per-file statistics are stored in structures of type <code class="literal">DB_MPOOL_FSTAT</code>.
The following <code class="literal">DB_MPOOL_FSTAT</code> fields will be filled in for each file in
the cache; that is, each element of the array:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="bold"><strong>char * file_name;</strong></span>
</p>
<p>
The name of the file.
</p>
</li>
<li>
<p>
<span class="bold"><strong>size_t st_pagesize;</strong></span>
</p>
<p>
Page size in bytes.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_cache_hit;</strong></span>
</p>
<p>
Requested pages found in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_cache_miss;</strong></span>
</p>
<p>
Requested pages not found in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>u_int32_t st_map;</strong></span>
</p>
<p>
Requested pages mapped into the process' address space.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_create;</strong></span>
</p>
<p>
Pages created in the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_in;</strong></span>
</p>
<p>
Pages read into the cache.
</p>
</li>
<li>
<p>
<span class="bold"><strong>uintmax_t st_page_out;</strong></span>
</p>
<p>
Pages written from the cache to the backing file.
</p>
</li>
</ul>
</div>
<p>
The <code class="methodname">DbEnv::memp_stat()</code> method may not be called before the
<a class="xref" href="envopen.html" title="DbEnv::open()">DbEnv::open()</a> method is called.
</p>
<p>
The <code class="methodname">DbEnv::memp_stat()</code> <span>
<span>
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.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8737464"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8736672"></a>gsp</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>gsp</strong></span> parameter references memory
into which a pointer to the allocated global statistics structure is
copied.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8740576"></a>fsp</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>fsp</strong></span> parameter references memory
into which a pointer to the allocated per-file statistics structures
is copied.
</p>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8741352"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or the following value:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="mempstat_DB_STAT_CLEAR"></a>
<code class="literal">DB_STAT_CLEAR</code>
</p>
<p>
Reset statistics after returning their values.
</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8746472"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">DbEnv::memp_stat()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="idp8754336"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8753040"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="env.html" title="Chapter 5. The DbEnv Handle">DbEnv</a>, <a class="link" href="memp.html" title="Chapter 9. The DbMpoolFile Handle">DbMpoolFile</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idp8726936"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="memp.html#memplist" title="Memory Pools and Related Methods">Memory Pools and Related Methods</a>
</p>
</div>
</div>
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