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< p > Library Version 11.2.5.2< / p >
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< th colspan = "3" align = "center" > DB_MPOOLFILE-> get()< / th >
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< td width = "20%" align = "left" > < a accesskey = "p" href = "mempfclose.html" > Prev< / a > < / td >
< th width = "60%" align = "center" > Chapter
The DB_MPOOLFILE Handle
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< div class = "sect1" lang = "en" xml:lang = "en" >
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< h2 class = "title" style = "clear: both" > < a id = "mempfget" > < / a > DB_MPOOLFILE-> get()< / h2 >
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< pre class = "programlisting" > #include < db.h>
int
DB_MPOOLFILE-> get(DB_MPOOLFILE *mpf,
db_pgno_t *pgnoaddr, DB_TXN * txnid, u_int32_t flags, void **pagep); < / pre >
< p >
The < code class = "methodname" > DB_MPOOLFILE-> get()< / code > method returns pages from the cache.
< / p >
< p >
All pages returned by < code class = "methodname" > DB_MPOOLFILE-> get()< / code > will be retained (that is,
< span class = "emphasis" > < em > latched< / em > < / span > ) in the cache until a subsequent call to
< a class = "xref" href = "mempput.html" title = "DB_MPOOLFILE->put()" > DB_MPOOLFILE-> put()< / a > .
There is no deadlock detection among latches so care must be taken in the application if the DB_MPOOL_DIRTY
or DB_MPOOL_EDIT flags are used as these get exlusive latches on the pages.
< / p >
< p >
The returned page is < span class = "bold" > < strong > size_t< / strong > < / span > type
aligned.
< / p >
< p >
Fully or partially created pages have all their bytes set to a nul
byte, unless the
< a class = "xref" href = "mempset_clear_len.html" title = "DB_MPOOLFILE->set_clear_len()" > DB_MPOOLFILE-> set_clear_len()< / a >
method was called to specify other behavior before the file was
opened.
< / p >
< p > < a id = "fget_DB_PAGE_NOTFOUND" > < / a >
The < code class = "methodname" > DB_MPOOLFILE-> get()< / code > method will return
< code class = "literal" > DB_PAGE_NOTFOUND< / code > if the requested page does not exist and DB_MPOOL_CREATE
was not set. Unless otherwise specified, the < code class = "methodname" > DB_MPOOLFILE-> get()< / code >
< span >
< span >
method returns a non-zero error value on failure and 0 on success.
< / span >
< / span >
< / p >
< div class = "sect2" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h3 class = "title" > < a id = "id3737059" > < / a > Parameters< / h3 >
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< / div >
< / div >
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< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737048" > < / a > flags< / h4 >
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< / div >
< / div >
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< p >
The < span class = "bold" > < strong > flags< / strong > < / span > parameter must be set to 0
or by bitwise inclusively < span class = "bold" > < strong > OR< / strong > < / span > 'ing
together one or more of the following values:
< / p >
< div class = "itemizedlist" >
< ul type = "disc" >
< li >
< p > < a id = "mpoolfget_DB_MPOOL_CREATE" > < / a >
< code class = "literal" > DB_MPOOL_CREATE< / code >
< / p >
< p >
If the specified page does not exist, create it. In this case, the
< a class = "link" href = "mempregister.html" title = "DB_ENV->memp_register()" > pgin< / a > method, if
specified, is called.
< / p >
< / li >
< li >
< p > < a id = "fget_DB_MPOOL_DIRTY" > < / a >
< code class = "literal" > DB_MPOOL_DIRTY< / code >
< / p >
< p >
The page will be modified and must be written to the source file
before being evicted from the cache. For files open with the
< a class = "link" href = "dbopen.html#dbopen_DB_MULTIVERSION" > DB_MULTIVERSION< / a >
flag set, a new copy of the page will be made if this is the first
time the specified transaction is modifying it.
A page fetched with the < code class = "literal" > DB_MPOOL_DIRTY< / code > flag will be
< span class = "bold" > < strong > exclusively latched< / strong > < / span > until
a subsequent call to < a class = "xref" href = "mempput.html" title = "DB_MPOOLFILE->put()" > DB_MPOOLFILE-> put()< / a > .
< / p >
< / li >
< li >
< p > < a id = "fget_DB_MPOOL_EDIT" > < / a >
< code class = "literal" > DB_MPOOL_EDIT< / code >
< / p >
< p >
The page will be modified and must be written to the source file
before being evicted from the cache. No copy of the page will be made,
regardless of the
< a class = "link" href = "dbopen.html#dbopen_DB_MULTIVERSION" > DB_MULTIVERSION< / a >
setting. This flag is only intended for use in situations where a
transaction handle is not available, such as during aborts or
recovery.
A page fetched with the < code class = "literal" > DB_MPOOL_EDIT< / code > flag will be
< span class = "bold" > < strong > exclusively latched< / strong > < / span > until
a subsequent call to < a class = "xref" href = "mempput.html" title = "DB_MPOOLFILE->put()" > DB_MPOOLFILE-> put()< / a > .
< / p >
< / li >
< li >
< p > < a id = "fget_DB_MPOOL_LAST" > < / a >
< code class = "literal" > DB_MPOOL_LAST< / code >
< / p >
< p >
Return the last page of the source file, and copy its page number into
the memory location to which < span class = "bold" > < strong > pgnoaddr< / strong > < / span >
refers.
< / p >
< / li >
< li >
< p > < a id = "mpoolfget_DB_MPOOL_NEW" > < / a >
< code class = "literal" > DB_MPOOL_NEW< / code >
< / p >
< p >
Create a new page in the file, and copy its page number into the
memory location to which < span class = "bold" > < strong > pgnoaddr< / strong > < / span >
refers. In this case, the < code class = "literal" > pgin_fcn< / code > callback, if specified on
< a class = "xref" href = "mempregister.html" title = "DB_ENV->memp_register()" > DB_ENV-> memp_register()< / a > , is
< span class = "bold" > < strong > not< / strong > < / span > called.
< / p >
< / li >
< / ul >
< / div >
< p >
The < code class = "literal" > DB_MPOOL_CREATE< / code > , < code class = "literal" > DB_MPOOL_LAST< / code > , and
< code class = "literal" > DB_MPOOL_NEW< / code > flags are mutually exclusive.
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737148" > < / a > pagep< / h4 >
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< / div >
< / div >
< / div >
< p >
The < span class = "bold" > < strong > pagep< / strong > < / span > parameter references memory
into which a pointer to the returned page is copied.
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737310" > < / a > pgnoaddr< / h4 >
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< / div >
< / div >
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< p >
If the < span class = "bold" > < strong > flags< / strong > < / span > parameter is set to
< code class = "literal" > DB_MPOOL_LAST< / code > or < code class = "literal" > DB_MPOOL_NEW< / code > , the
page number of the created page is copied into the memory location to
which the < span class = "bold" > < strong > pgnoaddr< / strong > < / span > parameter refers.
Otherwise, the < span class = "bold" > < strong > pgnoaddr< / strong > < / span > parameter is the
page to create or retrieve.
< / p >
< div class = "note" style = "margin-left: 0.5in; margin-right: 0.5in;" >
< h3 class = "title" > Note< / h3 >
< p >
Page numbers begin at 0; that is, the first page in the file is page number 0,
not page number 1.
< / p >
< / div >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737142" > < / a > txnid< / h4 >
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< / div >
< / div >
< / div >
< p >
If the operation is part of an application-specified transaction, the
< span class = "bold" > < strong > txnid< / strong > < / span > parameter is a transaction
handle returned from < a class = "xref" href = "txnbegin.html" title = "DB_ENV->txn_begin()" > DB_ENV-> txn_begin()< / a > ;
otherwise NULL. A transaction is required if the file is open for multiversion
concurrency control by passing
< a class = "link" href = "dbopen.html#dbopen_DB_MULTIVERSION" > DB_MULTIVERSION< / a >
to
< a class = "xref" href = "mempfopen.html" title = "DB_MPOOLFILE->open()" > DB_MPOOLFILE-> open()< / a >
and the DB_MPOOL_DIRTY, DB_MPOOL_CREATE or DB_MPOOL_NEW flags were
specified. Otherwise it is ignored.
< / p >
< / div >
< / div >
< div class = "sect2" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h3 class = "title" > < a id = "id3737361" > < / a > Errors< / h3 >
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< / div >
< / div >
< / div >
< p >
The < code class = "methodname" > DB_MPOOLFILE-> get()< / code > < span >
< span >
method may fail and return one of the following non-zero errors:
< / span >
< / span >
< / p >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737237" > < / a > EACCES< / h4 >
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< / div >
< / div >
< / div >
< p >
The < code class = "literal" > DB_MPOOL_DIRTY< / code > or
< code class = "literal" > DB_MPOOL_EDIT< / code > flag was set and the source file was
not opened for writing.
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737270" > < / a > EAGAIN< / h4 >
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< / div >
< / div >
< / div >
< p >
The page reference count has overflowed. (This should never happen
unless there is a bug in the application.)
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737518" > < / a > EINVAL< / h4 >
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< / div >
< / div >
< / div >
< p >
If the < code class = "literal" > DB_MPOOL_NEW< / code > flag was set, and the source
file was not opened for writing; more than one of
< code class = "literal" > DB_MPOOL_CREATE< / code > , < code class = "literal" > DB_MPOOL_LAST< / code > ,
and < code class = "literal" > DB_MPOOL_NEW< / code > was set; or if an invalid flag
value or parameter was specified.
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3736503" > < / a > DB_LOCK_DEADLOCK< / h4 >
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< / div >
< / div >
< / div >
< p >
For transactions configured with
< a class = "link" href = "txnbegin.html#txnbegin_DB_TXN_SNAPSHOT" > DB_TXN_SNAPSHOT< / a > ,
the page has been modified since the transaction began.
< / p >
< / div >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h4 class = "title" > < a id = "id3737241" > < / a > ENOMEM< / h4 >
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< / div >
< / div >
< / div >
< p >
The cache is full, and no more pages will fit in the cache.
< / p >
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< div class = "sect2" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h3 class = "title" > < a id = "id3737094" > < / a > Class< / h3 >
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< / div >
< / div >
< / div >
< p >
< a class = "link" href = "env.html" title = "Chapter > DB_ENV< / a > , < a class = "link" href = "memp.html" title = "Chapter > DB_MPOOLFILE< / a >
< / p >
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< div class = "sect2" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
< div >
< div >
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< h3 class = "title" > < a id = "id3737402" > < / a > See Also< / h3 >
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< / div >
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< p >
< a class = "xref" href = "memp.html#memplist" title = "Memory Pools and Related Methods" > Memory Pools and Related Methods< / a >
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