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| author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2015-02-17 17:25:57 +0000 |
|---|---|---|
| committer | <> | 2015-03-17 16:26:24 +0000 |
| commit | 780b92ada9afcf1d58085a83a0b9e6bc982203d1 (patch) | |
| tree | 598f8b9fa431b228d29897e798de4ac0c1d3d970 /docs/programmer_reference/am_misc_partial.html | |
| parent | 7a2660ba9cc2dc03a69ddfcfd95369395cc87444 (diff) | |
| download | berkeleydb-master.tar.gz | |
Diffstat (limited to 'docs/programmer_reference/am_misc_partial.html')
| -rw-r--r-- | docs/programmer_reference/am_misc_partial.html | 93 |
1 files changed, 53 insertions, 40 deletions
diff --git a/docs/programmer_reference/am_misc_partial.html b/docs/programmer_reference/am_misc_partial.html index 1169f460..ab128bf8 100644 --- a/docs/programmer_reference/am_misc_partial.html +++ b/docs/programmer_reference/am_misc_partial.html @@ -14,17 +14,16 @@ <body> <div xmlns="" class="navheader"> <div class="libver"> - <p>Library Version 11.2.5.3</p> + <p>Library Version 12.1.6.1</p> </div> <table width="100%" summary="Navigation header"> <tr> - <th colspan="3" align="center">Partial record storage and retrieval</th> + <th colspan="3" align="center">Partial record storage and + retrieval</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="am_misc_bulk.html">Prev</a> </td> - <th width="60%" align="center">Chapter 4. - Access Method Wrapup - </th> + <th width="60%" align="center">Chapter 4. Access Method Wrapup </th> <td width="20%" align="right"> <a accesskey="n" href="am_misc_struct.html">Next</a></td> </tr> </table> @@ -34,44 +33,57 @@ <div class="titlepage"> <div> <div> - <h2 class="title" style="clear: both"><a id="am_misc_partial"></a>Partial record storage and retrieval</h2> + <h2 class="title" style="clear: both"><a id="am_misc_partial"></a>Partial record storage and + retrieval</h2> </div> </div> </div> - <p>It is possible to both store and retrieve parts of data items in all -Berkeley DB access methods. This is done by setting the -<a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag <a href="../api_reference/C/dbt.html" class="olink">DBT</a> structure passed to the -Berkeley DB method.</p> - <p>The <a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag is based on the values of two fields -of the <a href="../api_reference/C/dbt.html" class="olink">DBT</a> structure: <span class="bold"><strong>dlen</strong></span> and <span class="bold"><strong>doff</strong></span>. The value -of <span class="bold"><strong>dlen</strong></span> is the number of bytes of the record in which the -application is interested. The value of <span class="bold"><strong>doff</strong></span> is the offset from -the beginning of the data item where those bytes start.</p> - <p>For example, if the data item were <span class="bold"><strong>ABCDEFGHIJKL</strong></span>, a <span class="bold"><strong>doff</strong></span> -value of 3 would indicate that the bytes of interest started at -<span class="bold"><strong>D</strong></span>, and a <span class="bold"><strong>dlen</strong></span> value of 4 would indicate that the bytes -of interest were <span class="bold"><strong>DEFG</strong></span>.</p> - <p>When retrieving a data item from a database, the <span class="bold"><strong>dlen</strong></span> bytes -starting <span class="bold"><strong>doff</strong></span> bytes from the beginning of the record are -returned, as if they comprised the entire record. If any or all of the -specified bytes do not exist in the record, the retrieval is still -successful and any existing bytes are returned.</p> - <p>When storing a data item into the database, the <span class="bold"><strong>dlen</strong></span> bytes -starting <span class="bold"><strong>doff</strong></span> bytes from the beginning of the specified key's -data record are replaced by the data specified by the <span class="bold"><strong>data</strong></span> and -<span class="bold"><strong>size</strong></span> fields. If <span class="bold"><strong>dlen</strong></span> is smaller than <span class="bold"><strong>size</strong></span>, the -record will grow, and if <span class="bold"><strong>dlen</strong></span> is larger than <span class="bold"><strong>size</strong></span>, the -record will shrink. If the specified bytes do not exist, the record will -be extended using nul bytes as necessary, and the store call will still -succeed.</p> - <p>The following are various examples of the put case for the -<a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag. In all examples, the initial data item is 20 -bytes in length:</p> <p> - <span class="bold"> - <strong>ABCDEFGHIJ0123456789</strong> - </span> - </p> + It is possible to both store and retrieve parts of data + items in all Berkeley DB access methods. This is done by + setting the <a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag <a href="../api_reference/C/dbt.html" class="olink">DBT</a> structure passed to + the Berkeley DB method. + </p> + <p> + The <a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag is based on the values of two + fields of the <a href="../api_reference/C/dbt.html" class="olink">DBT</a> structure: <span class="bold"><strong>dlen</strong></span> + and <span class="bold"><strong>doff</strong></span>. The value of <span class="bold"><strong> + dlen</strong></span> is the number of bytes of the record in + which the application is interested. The value of <span class="bold"><strong>doff</strong></span> is the offset from the + beginning of the data item where those bytes start. + </p> + <p> + For example, if the data item were <span class="bold"><strong> + ABCDEFGHIJKL</strong></span>, a <span class="bold"><strong>doff</strong></span> + value of 3 would indicate that the bytes + of interest started at <span class="bold"><strong>D</strong></span>, and + a <span class="bold"><strong>dlen</strong></span> value of 4 would + indicate that the bytes of interest were <span class="bold"><strong> + DEFG</strong></span>. + </p> + <p> + When retrieving a data item from a database, the <span class="bold"><strong>dlen</strong></span> bytes starting <span class="bold"><strong>doff</strong></span> bytes from the beginning of + the record are returned, as if they comprised the entire + record. If any or all of the specified bytes do not exist in + the record, the retrieval is still successful and any existing + bytes are returned. + </p> + <p> + When storing a data item into the database, the <span class="bold"><strong>dlen</strong></span> bytes starting <span class="bold"><strong>doff</strong></span> bytes from the beginning of + the specified key's data record are replaced by the data + specified by the <span class="bold"><strong>data</strong></span> and + <span class="bold"><strong>size</strong></span> fields. If <span class="bold"><strong>dlen</strong></span> is smaller than <span class="bold"><strong>size</strong></span>, the record will grow, and if + <span class="bold"><strong>dlen</strong></span> is larger than + <span class="bold"><strong>size</strong></span>, the record will + shrink. If the specified bytes do not exist, the record will + be extended using nul bytes as necessary, and the store call + will still succeed. + </p> + <p> + The following are various examples of the put case for the + <a href="../api_reference/C/dbt.html#dbt_DB_DBT_PARTIAL" class="olink">DB_DBT_PARTIAL</a> flag. In all examples, the initial data item + is 20 bytes in length: <span class="bold"><strong>ABCDEFGHIJ0123456789</strong></span> + </p> <div class="orderedlist"> <ol type="1"> <li> @@ -182,7 +194,8 @@ ABCDEFGHIJ0123456789 -> ABCDEFGHIJ0123456789\0\0\0\0\0abcdefghij </pre> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> - <td width="40%" align="right" valign="top"> Storing C/C++ structures/objects</td> + <td width="40%" align="right" valign="top"> Storing C/C++ + structures/objects</td> </tr> </table> </div> |