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Import of Sleepycat DB 2.4.14.1
1998-10-15 07:56:37 +04:00
<HTML>
<HEAD>
<TITLE>db_mpool</TITLE>
</HEAD>
<BODY BGCOLOR=white>
<H1>db_mpool</H1>
<HR SIZE=1 NOSHADE>
<PRE>
<!-- Manpage converted by man2html 3.0.1 -->
<B>#include</B> <B>&lt;db.h&gt;</B>
<B>int</B>
<B>memp</B>_<B>open(char</B> <B>*dir,</B>
<B>u</B>_<B>int32</B>_<B>t</B> <B>flags,</B> <B>int</B> <B>mode,</B> <B>DB</B>_<B>ENV</B> <B>*dbenv,</B> <B>DB</B>_<B>MPOOL</B> <B>**regionp);</B>
<B>int</B>
<B>memp</B>_<B>close(DB</B>_<B>MPOOL</B> <B>*mp);</B>
<B>int</B>
<B>memp</B>_<B>fopen(DB</B>_<B>MPOOL</B> <B>*mp,</B> <B>char</B> <B>*file,</B> <B>u</B>_<B>int32</B>_<B>t</B> <B>flags,</B> <B>int</B> <B>mode,</B>
<B>size</B>_<B>t</B> <B>pagesize,</B> <B>DB</B>_<B>MPOOL</B>_<B>FINFO</B> <B>*finfop,</B> <B>DB</B>_<B>MPOOLFILE</B> <B>**mpf);</B>
<B>int</B>
<B>memp</B>_<B>fclose(DB</B>_<B>MPOOLFILE</B> <B>*mpf);</B>
<B>int</B>
<B>memp</B>_<B>fget(DB</B>_<B>MPOOLFILE</B> <B>*mpf,</B>
<B>db</B>_<B>pgno</B>_<B>t</B> <B>*pgnoaddr,</B> <B>u</B>_<B>int32</B>_<B>t</B> <B>flags,</B> <B>void</B> <B>**pagep);</B>
<B>int</B>
<B>memp</B>_<B>fput(DB</B>_<B>MPOOLFILE</B> <B>*mpf,</B> <B>void</B> <B>*pgaddr,</B> <B>u</B>_<B>int32</B>_<B>t</B> <B>flags);</B>
<B>int</B>
<B>memp</B>_<B>fset(DB</B>_<B>MPOOLFILE</B> <B>*mpf,</B> <B>void</B> <B>*pgaddr,</B> <B>u</B>_<B>int32</B>_<B>t</B> <B>flags);</B>
<B>int</B>
<B>memp</B>_<B>fsync(DB</B>_<B>MPOOLFILE</B> <B>*mpf);</B>
<B>int</B>
<B>memp</B>_<B>unlink(const</B> <B>char</B> <B>*dir,</B> <B>int</B> <B>force,</B> <B>DB</B>_<B>ENV</B> <B>*);</B>
<B>int</B>
<B>memp</B>_<B>register(DB</B>_<B>MPOOL</B> <B>*mp,</B> <B>int</B> <B>ftype,</B>
<B>int</B> <B>(*pgin)(db</B>_<B>pgno</B>_<B>t</B> <B>pgno,</B> <B>void</B> <B>*pgaddr,</B> <B>DBT</B> <B>*pgcookie),</B>
<B>int</B> <B>(*pgout)(db</B>_<B>pgno</B>_<B>t</B> <B>pgno,</B> <B>void</B> <B>*pgaddr,</B> <B>DBT</B> <B>*pgcookie));</B>
<B>int</B>
<B>memp</B>_<B>trickle(DB</B>_<B>MPOOL</B> <B>*mp,</B> <B>int</B> <B>pct,</B> <B>int</B> <B>*nwrotep);</B>
<B>int</B>
<B>memp</B>_<B>sync(DB</B>_<B>MPOOL</B> <B>*mp,</B> <B>LSN</B> <B>*lsn);</B>
<B>int</B>
<B>memp</B>_<B>stat(DB</B>_<B>MPOOL</B> <B>*mp,</B> <B>DB</B>_<B>MPOOL</B>_<B>STAT</B> <B>**gsp,</B>
<B>DB</B>_<B>MPOOL</B>_<B>FSTAT</B> <B>*(*fsp)[],</B> <B>void</B> <B>*(*db</B>_<B>malloc)(size</B>_<B>t));</B>
</PRE>
<H2>DESCRIPTION</H2><PRE>
The DB library is a family of groups of functions that
provides a modular programming interface to transactions
and record-oriented file access. The library includes
support for transactions, locking, logging and file page
caching, as well as various indexed access methods. Many
of the functional groups (e.g., the file page caching
functions) are useful independent of the other DB
functions, although some functional groups are explicitly
based on other functional groups (e.g., transactions and
logging). For a general description of the DB package,
see <B><A HREF="db_intro.html">db_intro(3)</A></B>.
This manual page describes the specific details of the
memory pool interface.
The db_mpool functions are the library interface intended
to provide general-purpose, page-oriented buffer
management of one or more files. While designed to work
with the other DB functions, these functions are also
useful for more general purposes. The memory pools
(DB_MPOOL's) are referred to in this document as simply
``pools''. Pools may be shared between processes. Pools
are usually filled by pages from one or more files
(DB_MPOOLFILE's). Pages in the pool are replaced in LRU
(least-recently-used) order, with each new page replacing
the page that has been unused the longest. Pages
retrieved from the pool using memp_fget are ``pinned'' in
the pool, by default, until they are returned to the
pool's control using the memp_fput function.
memp_open
The memp_open function copies a pointer, to the memory
pool identified by the <B>directory</B> dir, into the memory
location referenced by regionp.
If the dbenv argument to memp_open was initialized using
db_appinit, dir is interpreted as described by
<B><A HREF="db_appinit.html">db_appinit(3)</A></B>.
Otherwise, if dir is not NULL, it is interpreted relative
to the current working directory of the process. If dir
is NULL, the following environment variables are checked
in order: ``TMPDIR'', ``TEMP'', and ``TMP''. If one of
them is set, memory pool files are created relative to the
directory it specifies. If none of them are set, the
first possible one of the following directories is used:
/var/tmp, /usr/tmp, /temp, /tmp, C:/temp and C:/tmp.
All files associated with the memory pool are created in
this directory. This directory must already exist when
memory pool_open is called. If the memory pool already
exists, the process must have permission to read and write
the existing files. If the memory pool does not already
exist, it is optionally created and initialized.
The flags and mode arguments specify how files will be
opened and/or created when they don't already exist. The
flags value is specified by <B>or</B>'ing together one or more of
the following values:
DB_CREATE
Create any underlying files, as necessary. If the
files do not already exist and the DB_CREATE flag is
not specified, the call will fail.
DB_MPOOL_PRIVATE
Create a private MPOOL that is not shared with any
other process (although it may be shared with other
threads).
DB_NOMMAP
Always copy files in this memory pool into the local
cache instead of mapping them into process memory
(see the description of the mp_mmapsize field of the
DB_ENV structure for further information).
DB_THREAD
Cause the DB_MPOOL handle returned by the memp_open
function to be useable by multiple threads within a
single address space, i.e., to be ``free-threaded''.
All files created by the memory pool subsystem (other than
files created by the memp_fopen function, which are
separately specified) are created with mode mode (as
described in <B>chmod(2)</B>) and modified by the process' umask
value at the time of creation (see <B>umask(2)</B>). The group
ownership of created files is based on the system and
directory defaults, and is not further specified by DB.
The memory pool subsystem is configured based on the dbenv
argument to memp_open, which is a pointer to a structure
of type DB_ENV (typedef'd in &lt;db.h&gt;). Applications will
normally use the same DB_ENV structure (initialized by
<B><A HREF="db_appinit.html">db_appinit(3)</A></B>), as an argument to all of the subsystems in
the DB package.
References to the DB_ENV structure are maintained by DB,
so it may not be discarded until the last close function,
corresponding to an open function for which it was an
argument, has returned. In order to ensure compatibility
with future releases of DB, all fields of the DB_ENV
structure that are not explicitly set should be
initialized to 0 before the first time the structure is
used. Do this by declaring the structure external or
static, or by calling the C library routine <B>bzero(3)</B> or
<B>memset(3)</B>.
The fields of the DB_ENV structure used by memp_open are
described below. If dbenv is NULL or any of its fields
are set to 0, defaults appropriate for the system are used
where possible.
The following fields in the DB_ENV structure may be
initialized before calling memp_open:
void *(*db_errcall)(char *db_errpfx, char *buffer);
FILE *db_errfile;
const char *db_errpfx;
int db_verbose;
The error fields of the DB_ENV behave as described
for <B><A HREF="db_appinit.html">db_appinit(3)</A></B>.
size_t mp_mmapsize;
Files that are opened read-only in the pool (and that
satisfy a few other criteria) are, by default, mapped
into the process address space instead of being
copied into the local cache. This can result in
better-than-usual performance, as available virtual
memory is normally much larger than the local cache,
and page faults are faster than page copying on many
systems. However, in the presence of limited virtual
memory it can cause resource starvation, and in the
presence of large databases, it can result in immense
process sizes. If mp_mmapsize is non-zero, it
specifies the maximum file size, in bytes, for a file
to be mapped into the process address space. By
default, it is set to 10Mb.
size_t mp_size;
The suggested size of the pool, in bytes. This
should be the size of the normal working data set of
the application, with some small amount of additional
memory for unusual situations. (Note, the working
set is not the same as the number of simultaneously
referenced pages, and should be quite a bit larger!)
The default cache size is 128K bytes (16 8K byte
pages), and may not be less than 20K bytes.
The memp_open function returns the value of errno on
failure and 0 on success.
memp_close
The memp_close function closes the pool indicated by the
DB_MPOOL pointer mp, as returned by memp_open. This
function does not imply a call to memp_fsync, but does
imply a call to memp_fclose for any remaining open
DB_MPOOLFILE pointers returned to this process by calls to
memp_fopen.
In addition, if the dir argument to memp_open was NULL and
dbenv was not initialized using db_appinit, or the
DB_MPOOL_PRIVATE flag was set, all files created for this
shared region will be removed, as if memp_unlink were
called.
When multiple threads are using the DB_MPOOL handle
concurrently, only a single thread may call the memp_close
function.
The memp_close function returns the value of errno on
failure and 0 on success.
memp_fopen
The memp_fopen function opens a file in the pool specified
by the DB_MPOOL argument, copying the DB_MPOOLFILE pointer
representing it into the memory location referenced by
mpf.
The file argument is the name of the file to be opened.
If file is NULL, a private file is created that cannot be
shared with any other process (although it may be shared
with other threads).
The flags and mode arguments specify how files will be
opened and/or created when they don't already exist. The
flags value is specified by <B>or</B>'ing together one or more of
the following values:
DB_CREATE
Create any underlying files, as necessary. If the
files do not already exist and the DB_CREATE flag is
not specified, the call will fail.
DB_NOMMAP
Always copy this file into the local cache instead of
mapping it into process memory (see the description
of the mp_mmapsize field of the DB_ENV structure for
further information).
DB_RDONLY
Open any underlying files for reading only. Any
attempt to write the file using the pool functions
will fail, regardless of the actual permissions of
the file.
All files created by the function memp_fopen are created
with mode mode (as described in <B>chmod(2)</B>) and modified by
the process' umask value at the time of creation (see
<B>umask(2)</B>). The group ownership of created files is based
on the system and directory defaults, and is not further
specified by DB.
The pagesize argument is the size, in bytes, of the unit
of transfer between the application and the pool, although
it is not necessarily the unit of transfer between the
pool and the source file.
Files opened in the pool may be further configured based
on the finfop argument to memp_fopen, which is a pointer
to a structure of type DB_MPOOL_FINFO (typedef'd in
&lt;db.h&gt;). No references to the finfop structure are
maintained by DB, so it may be discarded when the
memp_fopen function returns. In order to ensure
compatibility with future releases of DB, all fields of
the DB_MPOOL_FINFO structure that are not explicitly set
should be initialized to 0 before the first time the
structure is used. Do this by declaring the structure
external or static, or by calling the C library routine
<B>bzero(3)</B> or <B>memset(3)</B>.
The fields of the DB_MPOOL_FINFO structure used by
memp_fopen are described below. If finfop is NULL or any
of its fields are set to their default value, defaults
appropriate for the system are used.
int ftype;
The ftype field should be the same as a ftype
argument previously specified to the memp_register
function, unless no input or output processing of the
file's pages are necessary, in which case it should
be 0. (See the description of the memp_register
function for more information.)
DBT *pgcookie;
The pgcookie field contains the byte string that is
passed to the pgin and pgout functions for this file,
if any. If no pgin or pgout functions are specified,
the pgcookie field should be NULL. (See the
description of the memp_register function for more
information.)
u_int8_t *fileid;
The fileid field is a unique identifier for the file.
The mpool functions must be able to uniquely identify
files in order that multiple processes sharing a file
will correctly share its underlying pages. Normally,
the fileid field should be NULL and the mpool
functions will use the file's device and inode
numbers (see <B>stat(2)</B>) for this purpose. On some
filesystems, (e.g., FAT or NFS) file device and inode
numbers are not necessarily unique across system
reboots. <B>Applications</B> <B>wanting</B> <B>to</B> <B>maintain</B> <B>a</B> <B>shared</B>
<B>memory</B> <B>buffer</B> <B>pool</B> <B>across</B> <B>system</B> <B>reboots,</B> <B>where</B> <B>the</B>
<B>pool</B> <B>contains</B> <B>pages</B> <B>from</B> <B>files</B> <B>stored</B> <B>on</B> <B>such</B>
<B>filesystems,</B> <B>must</B> <B>specify</B> <B>a</B> <B>unique</B> <B>file</B> <B>identifier</B> <B>to</B>
<B>the</B> memp_fopen call and each process opening or
registering the file must provide the same unique
identifier. If the fileid field is non-NULL, it must
reference a DB_FILE_ID_LEN (as defined in &lt;db.h&gt;)
length array of bytes that will be used to uniquely
identify the file. This should not be necessary for
most applications. Specifically, it is not necessary
if the memory pool is re-instantiated after each
system reboot, the application is using the DB access
methods instead of calling the pool functions
explicitly, or the files in the memory pool are
stored on filesystems where the file device and inode
numbers do not change across system reboots.
int32_t lsn_offset;
The lsn_offset field is the zero-based byte offset in
the page of the page's log sequence number (LSN), or
-1 if no LSN offset is specified. (See the
description of the memp_sync function for more
information.)
u_int32_t clear_len;
The clear_len field is the number of initial bytes in
a page that should be set to zero when the page is
created as a result of the DB_MPOOL_CREATE or
DB_MPOOL_NEW flags being specified to memp_fget. If
finfop is NULL or clear_len is 0, the entire page is
cleared.
The memp_fopen function returns the value of errno on
failure and 0 on success.
memp_fclose
The memp_fclose function closes the source file indicated
by the DB_MPOOLFILE pointer mpf. This function does not
imply a call to memp_fsync, i.e. no pages are written to
the source file as as a result of calling memp_fclose.
In addition, if the file argument to memp_fopen was NULL,
any underlying files created for this DB_MPOOLFILE will be
removed.
The memp_fclose function returns the value of errno on
failure and 0 on success.
memp_fget
The memp_fget function copies a pointer to the page with
the page number specified by pgnoaddr, from the source
file specified by the DB_MPOOLFILE pointer mpf, into the
memory location referenced by pagep. If the page does not
exist or cannot be retrieved, memp_fget will fail.
The returned page is size_t type aligned.
<B>Page</B> <B>numbers</B> <B>begin</B> <B>at</B> <B>0,</B> <B>e.g.,</B> <B>the</B> <B>first</B> <B>page</B> <B>in</B> <B>the</B> <B>file</B>
<B>is</B> <B>page</B> <B>number</B> <B>0,</B> <B>not</B> <B>page</B> <B>number</B> <B>1.</B>
The flags argument is specified by <B>or</B>'ing together one or
more of the following values:
DB_MPOOL_CREATE
If the specified page does not exist, create it. In
this case, the pgin function, if specified, is
called.
DB_MPOOL_LAST
Return the last page of the source file and copy its
page number to the location referenced by pgnoaddr.
DB_MPOOL_NEW
Create a new page in the file and copy its page
number to the location referenced by pgnoaddr. In
this case, the pgin function, if specified, is not
called.
The DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW flags
are mutually exclusive.
Created pages have all their bytes set to 0, unless
otherwise specified when the file was opened.
All pages returned by memp_fget will be retained (i.e.
``pinned'') in the pool until a subsequent call to
memp_fput.
The memp_fget function returns the value of errno on
failure and 0 on success.
memp_fput
The memp_fput function indicates that the page referenced
by pgaddr can be evicted from the pool. Pgaddr must be an
address previously returned by memp_fget.
The flags argument is specified by <B>or</B>'ing together one or
more of the following values:
DB_MPOOL_CLEAN
Clear any previously set modification information
(i.e., don't bother writing the page back to the
source file).
DB_MPOOL_DIRTY
The page has been modified and must be written to the
source file before being evicted from the pool.
DB_MPOOL_DISCARD
The page is unlikely to be useful in the near future,
and should be discarded before other pages in the
pool.
The DB_MPOOL_CLEAN and DB_MPOOL_DIRTY flags are mutually
exclusive.
The memp_fput function returns the value of errno on
failure and 0 on success.
memp_fset
The memp_fset function sets the flags associated with the
page referenced by pgaddr without unpinning it from the
pool. Pgaddr must be an address previously returned by
memp_fget. The flags argument to memp_fset is specified
by <B>or</B>'ing together one or more of the values specified as
flags for the memp_fput call.
The memp_fset function returns the value of errno on
failure and 0 on success.
memp_fsync
The memp_fsync function writes all pages associated with
the DB_MPOOLFILE pointer mpf, that were marked as modified
using memp_fput or memp_fset, back to the source file. If
any of the modified pages are also pinned (i.e., currently
referenced by this or another process) memp_fsync will
ignore them.
The memp_fsync function returns the value of errno on
failure, 0 on success, and DB_INCOMPLETE if there were
pages which were modified but which memp_fsync was unable
to write.
memp_unlink
The memp_unlink function destroys the memory pool
identified by the directory dir, removing all files used
to implement the memory pool. (The directory dir is not
removed.) If there are processes that have called
memp_open without calling memp_close (i.e., there are
processes currently using the memory pool), memp_unlink
will fail without further action, unless the force flag is
set, in which case memp_unlink will attempt to remove the
memory pool files regardless of any processes still using
the memory pool.
The result of attempting to forcibly destroy the region
when a process has the region open is unspecified.
Processes using a shared memory region maintain an open
file descriptor for it. On UNIX systems, the region
removal should succeed and processes that have already
joined the region should continue to run in the region
without change, however processes attempting to join the
memory pool will either fail or attempt to create a new
region. On other systems, e.g., WNT, where the <B>unlink(2)</B>
system call will fail if any process has an open file
descriptor for the file, the region removal will fail.
In the case of catastrophic or system failure, database
recovery must be performed (see <B><A HREF="db_recover.html">db_recover(1)</A></B> or the
DB_RECOVER and DB_RECOVER_FATAL flags to <B><A HREF="db_appinit.html">db_appinit(3)</A></B>).
Alternatively, if recovery is not required because no
database state is maintained across failures, it is
possible to clean up a memory pool by removing all of the
files in the directory specified to the memp_open
function, as memory pool files are never created in any
directory other than the one specified to memp_open.
Note, however, that this has the potential to remove files
created by the other DB subsystems in this database
environment.
The memp_unlink function returns the value of errno on
failure and 0 on success.
memp_register
The memp_register function registers page-in and page-out
functions for files of type ftype in the specified pool.
If the pgin function is non-NULL, it is called each time a
page is read into the memory pool from a file of type
ftype, or a page is created for a file of type ftype (see
the DB_MPOOL_CREATE flag for the memp_fget function). If
the pgout function is non-NULL, it is called each time a
page is written to a file of type ftype.
Both the pgin and pgout functions are called with the page
number, a pointer to the page being read or written, and
any argument pgcookie that was specified to the memp_fopen
function when the file was opened. The pgin and pgout
functions should return 0 on success, and an applicable
non-zero errno value on failure, in which case the
db_mpool function calling it will also fail, returning
that errno value.
The purpose of the memp_register function is to support
processing when pages are entered into, or flushed from,
the pool. A file type must be specified to make it
possible for unrelated threads or processes, that are
sharing a pool, to evict each other's pages from the pool.
Applications should call memp_register, during
initialization, for each type of file requiring input or
output processing that will be sharing the underlying
pool. (No registry is necessary for the standard access
method types, btree, hash and recno, as <B><A HREF="db_open.html">db_open(3)</A></B>
registers them separately.)
If a thread or process does not call memp_register for a
file type, it is impossible for it to evict pages for any
file requiring input or output processing from the pool.
For this reason, memp_register should always be called by
each application sharing a pool for each type of file
included in the pool, regardless of whether or not the
application itself uses files of that type.
There are no standard values for ftype, pgin, pgout and
pgcookie, except that the ftype value for a file must be a
non-zero positive number, as negative numbers are reserved
for internal use by the DB library. For this reason,
applications sharing a pool must coordinate their values
amongst themselves.
The memp_register function returns the value of errno on
failure and 0 on success.
memp_trickle
The memp_trickle function ensures that at least pct
percent of the pages in the shared memory pool are clean
by writing dirty pages to their backing files. If the
nwrotep argument is non-NULL, the number of pages that
were written to reach the correct percentage is returned
in the memory location it references.
The purpose of the memp_trickle function is to enable a
memory pool manager to ensure that a page is always
available for reading in new information without having to
wait for a write.
The memp_trickle function returns the value of errno on
failure and 0 on success.
memp_sync
The memp_sync function ensures that all the modified pages
in the pool with log sequence numbers (LSNs) less than the
lsn argument are written to disk.
The memp_sync function returns the value of errno on
failure, 0 on success, and DB_INCOMPLETE if there were
pages which need to be written but which memp_sync was
unable to write immediately. In addition, if memp_sync
returns success, the value of lsn will be overwritten with
the largest LSN from any page which was written by
memp_sync to satisfy this request.
The purpose of the memp_sync function is to enable a
transaction manager to ensure, as part of a checkpoint,
that all pages modified by a certain time have been
written to disk. Pages in the pool which cannot be
written back to disk immediately (e.g., are currently
pinned) are written to disk as soon as it is possible to
do so. The expected behavior of the transaction manager
is to call the memp_sync function and then, if the return
indicates that some pages could not be written
immediately, to wait briefly and retry again with the same
LSN until the memp_sync function returns that all pages
have been written.
To support the memp_sync functionality, it is necessary
that the pool functions know the location of the LSN on
the page for each file type. This location should be
specified when the file is opened using the memp_fopen
function. (Note, it is not required that the LSN be
aligned on the page in any way.)
memp_stat
The memp_stat function creates statistical structures and
copies pointers to them into user-specified memory
locations. The statistics include the number of files
participating in the pool, the active pages in the pool,
and information as to how effective the cache has been.
Statistical structures are created in allocated memory.
If db_malloc is non-NULL, it is called to allocate the
memory, otherwise, the library function <B>malloc(3)</B> is used.
The function db_malloc must match the calling conventions
of the <B>malloc(3)</B> library routine. Regardless, the caller
is responsible for deallocating the returned memory. To
deallocate the returned memory, free each returned memory
pointer; pointers inside the memory do not need to be
individually freed.
If gsp is non-NULL, the global statistics for the memory
pool mp are copied into the memory location it references.
The global statistics are stored in a structure of type
DB_MPOOL_STAT (typedef'd in &lt;db.h&gt;).
The following DB_MPOOL_STAT fields will be filled in:
u_int32_t st_refcnt;
The number of references to the region.
u_int32_t st_regsize;
The size of the region.
size_t st_cachesize;
Cache size in bytes.
u_int32_t st_cache_hit;
Requested pages found in the cache.
u_int32_t st_cache_miss;
Requested pages not found in the cache.
u_int32_t st_map;
Requested pages mapped into the process' address
space (there is no available information as to
whether or not this request caused disk I/O, although
examining the application page fault rate may be
helpful).
u_int32_t st_page_create;
Pages created in the cache.
u_int32_t st_page_in;
Pages read into the cache.
u_int32_t st_page_out;
Pages written from the cache to the backing file.
u_int32_t st_ro_evict;
Clean pages forced from the cache.
u_int32_t st_rw_evict;
Dirty pages forced from the cache.
u_int32_t st_hash_buckets;
Number of hash buckets in buffer hash table.
u_int32_t st_hash_searches;
Total number of buffer hash table lookups.
u_int32_t st_hash_longest;
The longest chain ever encountered in buffer hash
table lookups.
u_int32_t st_hash_examined;
Total number of hash elements traversed during hash
table lookups.
u_int32_t st_page_clean;
Clean pages currently in the cache.
u_int32_t st_page_dirty;
Dirty pages currently in the cache.
u_int32_t st_page_trickle;
Dirty pages written using the memp_trickle interface.
u_int32_t st_region_wait;
The number of times that a thread of control was
forced to wait before obtaining the region lock.
u_int32_t st_region_nowait;
The number of times that a thread of control was able
to obtain the region lock without waiting.
If fsp is non-NULL, a pointer to a NULL-terminated
variable length array of statistics for individual files,
in the memory pool mp, is copied into the memory location
it references. If no individual files currently exist in
the memory pool, fsp will be set to NULL.
The per-file statistics are stored in structures of type
DB_MPOOL_FSTAT (typedef'd in &lt;db.h&gt;). The following
DB_MPOOL_FSTAT fields will be filled in for each file in
the pool, i.e., each element of the array:
char *file_name;
The name of the file.
size_t st_pagesize;
Page size in bytes.
u_int32_t st_cache_hit;
Requested pages found in the cache.
u_int32_t st_cache_miss;
Requested pages not found in the cache.
u_int32_t st_map;
Requested pages mapped into the process' address
space.
u_int32_t st_page_create;
Pages created in the cache.
u_int32_t st_page_in;
Pages read into the cache.
u_int32_t st_page_out;
Pages written from the cache to the backing file.
The memp_stat function returns the value of errno on
failure and 0 on success.
</PRE>
<H2>ENVIRONMENT VARIABLES</H2><PRE>
The following environment variables affect the execution
of db_mpool:
DB_HOME
If the dbenv argument to memp_open was initialized
using db_appinit, the environment variable DB_HOME
may be used as the path of the database home for the
interpretation of the dir argument to memp_open, as
described in <B><A HREF="db_appinit.html">db_appinit(3)</A></B>.
TMPDIR
If the dbenv argument to memp_open was NULL or not
initialized using db_appinit, the environment
variable TMPDIR may be used as the directory in which
to create the memory pool, as described in the
memp_open section above.
</PRE>
<H2>ERRORS</H2><PRE>
The memp_open function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B><A HREF="db_appinit.html">db_version(3)</A></B>, <B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>,
<B><A HREF="db_log.html">log_compare(3)</A></B>, <B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>,
<B>memcmp(3)</B>, <B>memcpy(3)</B>, <B><A HREF="db_mpool.html">memp_close(3)</A></B>, <B><A HREF="db_mpool.html">memp_unlink(3)</A></B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>munmap(2)</B>, <B>open(2)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
In addition, the memp_open function may fail and return
errno for the following conditions:
[EAGAIN]
The shared memory region was locked and (repeatedly)
unavailable.
[EINVAL]
An invalid flag value or parameter was specified.
The DB_THREAD flag was specified and spinlocks are
not implemented for this architecture.
A NULL pathname was specified without the
DB_MPOOL_PRIVATE flag.
The specified cache size was impossibly small.
The memp_close function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B>close(2)</B>, <B>fcntl(2)</B>, <B>fflush(3)</B>, <B><A HREF="db_mpool.html">memp_fclose(3)</A></B>,
<B>munmap(2)</B>, and <B>strerror(3)</B>.
The memp_fopen function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcmp(3)</B>, <B>memcpy(3)</B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>open(2)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
In addition, the memp_fopen function may fail and return
errno for the following conditions:
[EINVAL]
An invalid flag value or parameter was specified.
The file has already been entered into the pool, and
the pagesize value is not the same as when the file
was entered into the pool, or the length of the file
is not zero or a multiple of the pagesize.
The DB_RDONLY flag was specified for an in-memory
pool.
The memp_fclose function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B>close(2)</B>, <B>fcntl(2)</B>, <B>fflush(3)</B>, <B>munmap(2)</B>, and
<B>strerror(3)</B>.
The memp_fget function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcmp(3)</B>, <B>memcpy(3)</B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>open(2)</B>, <B>read(2)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
In addition, the memp_fget function may fail and return
errno for the following conditions:
[EAGAIN]
The page reference count has overflowed. (This
should never happen unless there's a bug in the
application.)
[EINVAL]
An invalid flag value or parameter was specified.
The DB_MPOOL_NEW flag was set and the source file was
not opened for writing.
The requested page does not exist and DB_MPOOL_CREATE
was not set.
More than one of DB_MPOOL_CREATE, DB_MPOOL_LAST and
DB_MPOOL_NEW was set.
[ENOMEM]
The cache is full and no more pages will fit in the
pool.
The memp_fput function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcmp(3)</B>, <B>memcpy(3)</B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>open(2)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
In addition, the memp_fput function may fail and return
errno for the following conditions:
[EACCES]
The DB_MPOOL_DIRTY flag was set and the source file
was not opened for writing.
[EINVAL]
An invalid flag value or parameter was specified.
The pgaddr parameter does not reference a page
returned by memp_fget.
More than one of DB_MPOOL_CLEAN and DB_MPOOL_DIRTY
was set.
The memp_fset function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B>fcntl(2)</B>, and <B>fflush(3)</B>.
In addition, the memp_fset function may fail and return
errno for the following conditions:
[EINVAL]
An invalid flag value or parameter was specified.
The memp_fsync function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcpy(3)</B>, <B>memset(3)</B>,
<B>open(2)</B>, <B>qsort(3)</B>, <B>realloc(3)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
The memp_unlink function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B>close(2)</B>, <B>fcntl(2)</B>, <B>fflush(3)</B>, <B>malloc(3)</B>,
<B>memcpy(3)</B>, <B>memset(3)</B>, <B>mmap(2)</B>, <B>munmap(2)</B>, <B>open(2)</B>,
<B>sigfillset(3)</B>, <B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>,
<B>strdup(3)</B>, <B>strerror(3)</B>, <B>strlen(3)</B>, and <B>unlink(2)</B>.
In addition, the memp_unlink function may fail and return
errno for the following conditions:
[EBUSY]
The shared memory region was in use and the force
flag was not set.
The memp_register function may fail and return errno for
any of the errors specified for the following DB and
library functions: <B>fcntl(2)</B>, and <B>malloc(3)</B>.
The memp_trickle function may fail and return errno for
any of the errors specified for the following DB and
library functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>,
<B>close(2)</B>, <B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcmp(3)</B>, <B>memcpy(3)</B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>open(2)</B>, <B>sigfillset(3)</B>,
<B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>, <B>strdup(3)</B>,
<B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and <B>write(2)</B>.
In addition, the memp_trickle function may fail and return
errno for the following conditions:
[EINVAL]
An invalid flag value or parameter was specified.
The memp_sync function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B><A HREF="db_mpool.html">DBmemp-&gt;pgin(3)</A></B>, <B><A HREF="db_mpool.html">DBmemp-&gt;pgout(3)</A></B>, <B>close(2)</B>,
<B>fcntl(2)</B>, <B>fflush(3)</B>, <B>fsync(2)</B>, <B><A HREF="db_log.html">log_compare(3)</A></B>,
<B><A HREF="db_log.html">log_flush(3)</A></B>, <B>lseek(2)</B>, <B>malloc(3)</B>, <B>memcmp(3)</B>, <B>memcpy(3)</B>,
<B>memset(3)</B>, <B>mmap(2)</B>, <B>open(2)</B>, <B>qsort(3)</B>, <B>realloc(3)</B>,
<B>sigfillset(3)</B>, <B>sigprocmask(2)</B>, <B>stat(2)</B>, <B>strcpy(3)</B>,
<B>strdup(3)</B>, <B>strerror(3)</B>, <B>strlen(3)</B>, <B>time(3)</B>, <B>unlink(2)</B>, and
<B>write(2)</B>.
In addition, the memp_sync function may fail and return
errno for the following conditions:
[EINVAL]
An invalid flag value or parameter was specified.
The memp_sync function was called without logging
having been initialized in the environment.
The memp_stat function may fail and return errno for any
of the errors specified for the following DB and library
functions: <B>fcntl(2)</B>, <B>malloc(3)</B>, <B>memcpy(3)</B>, and <B>strlen(3)</B>.
</PRE>
<H2>SEE ALSO</H2><PRE>
<B><A HREF="db_archive.html">db_archive(1)</A></B>, <B><A HREF="db_checkpoint.html">db_checkpoint(1)</A></B>, <B><A HREF="db_deadlock.html">db_deadlock(1)</A></B>, <B><A HREF="db_dump.html">db_dump(1)</A></B>,
<B><A HREF="db_load.html">db_load(1)</A></B>, <B><A HREF="db_recover.html">db_recover(1)</A></B>, <B><A HREF="db_stat.html">db_stat(1)</A></B>, <B><A HREF="db_intro.html">db_intro(3)</A></B>,
<B><A HREF="db_appinit.html">db_appinit(3)</A></B>, <B><A HREF="db_cursor.html">db_cursor(3)</A></B>, <B><A HREF="db_dbm.html">db_dbm(3)</A></B>, <B><A HREF="db_internal.html">db_internal(3)</A></B>,
<B><A HREF="db_lock.html">db_lock(3)</A></B>, <B><A HREF="db_log.html">db_log(3)</A></B>, <B><A HREF="db_mpool.html">db_mpool(3)</A></B>, <B><A HREF="db_open.html">db_open(3)</A></B>, <B><A HREF="db_thread.html">db_thread(3)</A></B>,
<B><A HREF="db_txn.html">db_txn(3)</A></B>
</PRE>
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