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Overview
Comment:Update a statement in the provider limitations documentation regarding deferred transaction locking semantics. Fix for [425f060dec].
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SHA1: 45cc5a21fa9a4337b19b5bf607c5f8c4618d2617
User & Date: mistachkin 2014-07-02 17:45:06
References
2014-07-02
17:46 Closed ticket [425f060dec]: Documentation update - "Limitations of ..." plus 4 other changes artifact: 624c6b5775 user: mistachkin
Context
2014-07-18
22:04
Add initial performance tests for the SQLiteDataReader class. check-in: d3be3b1abe user: mistachkin tags: trunk
2014-07-02
17:45
Update a statement in the provider limitations documentation regarding deferred transaction locking semantics. Fix for [425f060dec]. check-in: 45cc5a21fa user: mistachkin tags: trunk
2014-06-23
22:55
Final updates for the 1.0.93.0 release. check-in: 47ba62f72c user: mistachkin tags: trunk, release, release-1.0.93.0
Changes
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Changes to Doc/Extra/Provider/limitations.html.

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          </td>
        </tr>
      </table>
    </div>
    <div id="mainSection">
    <div id="mainBody">
      <h1 class="heading">Limitations of this ADO.NET SQLite Data Provider</h1>
      <p>As providers go, this one doesn't have many restrictions. SQLite has no 
        support for row-level or table-level locks. When a connection locks the database for writing, no other connection or process may read or write to the database until the write operation is complete.  The SQLite.NET provider attempts to retry 
        internally if a database is locked, up to the CommandTimeout property of the 
        command in question.</p>
      <p>SQLite is inherently type-less, and only understands a few basic datatypes 
        natively. They are (in .NET-speak) Int64, Double, String and Blob. The 
        SQLite.NET provider will use the database schema information it can glean to 
        enforce type-ness, but it is an inexact science.</p>
      <p>
        Hierarchical DataReaders are not supported. In the 
        case of transactions, any SQLiteCommand created on a connection will (when 
        executed) automatically join a transaction in progress, regardless of whether 
        that transaction was created before or after the command.</p>
      <p>A SQLiteCommand object <b>can</b> be re-assigned a new SQLiteConnection object 
        as long as no DataReaders are active on the command.</p>
      <p>Opening a transaction is considered a write operation, so only use them when 
        you want to write to the database! If you hold open a transaction, all readers on other
        connections
        will be blocked until the transaction is closed!</p>
      <p></p>
      <h4 class="subHeading">Thread Safety</h4>
      <p>Multi-threading in SQLite must be done carefully. Here are the restrictions:</p>
      <ul>
        <li>
          <b>You May</b>
        Clone() a SQLiteConnection object in one thread and pass the cloned object to 
        another thread. Once passed, the other thread becomes the new owner of the 
        cloned connection, and the original thread must not keep a reference to the 
        clone or call any methods on the clone.
        <LI>
          <STRONG>You May</STRONG>
        create multiple threads, and those threads can create their own 
        SQLiteConnection and subsequent objects for accessing a database.&nbsp; 
        Multiple connections on multiple threads to the same database file are 
        perfectly&nbsp;acceptable&nbsp;and will behave predictably.&nbsp;
        <li>
          <b>You May NOT</b>
        call methods or properties or otherwise reference any SQLite provider classes 
        that belong to another thread.
        <li>
          <b>You May NOT</b> pass a SQLiteCommand, SQLiteDataReader, SQLiteDataAdapter or 
          any other SQLite provider class except a cloned SQLiteConnection to another 
          thread.</li>
      </ul>
      <p>Understand again that SQLite has no fine-grained locking mechanisms. It is 
        therefore your own responsibility in a multi-threaded environment to handle 
        potential timeouts that may occur if a long-running query in one thread 
        prevents a query in another thread from executing. These timeouts will only 
        occur if one thread is attempting to read while another thread is attempting to 
        write. Whichever thread got its lock first will be the one to execute, and the 
        other thread will block until the CommandTimeout value elapses or the other 
        thread finishes.</p>
      <hr/>
      <div id="footer">
        <p>
          <a href="mailto:sqlite-users@sqlite.org?subject=SQLite.NET%20Class%20Library%20Documentation%20Feedback:%20Limitations">
            Send comments on this topic.</a>
        </p>







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          </td>
        </tr>
      </table>
    </div>
    <div id="mainSection">
    <div id="mainBody">
      <h1 class="heading">Limitations of this ADO.NET SQLite Data Provider</h1>
      <p>As providers go, this one doesn't have many restrictions. SQLite has no
        support for row-level or table-level locks. When a connection locks the database for writing, no other connection or process may read or write to the database until the write operation is complete.  The SQLite.NET provider attempts to retry
        internally if a database is locked, up to the CommandTimeout property of the
        command in question.</p>
      <p>SQLite is inherently type-less, and only understands a few basic datatypes
        natively. They are (in .NET-speak) Int64, Double, String and Blob. The
        SQLite.NET provider will use the database schema information it can glean to
        enforce type-ness, but it is an inexact science.</p>
      <p>
        Hierarchical DataReaders are not supported. In the
        case of transactions, any SQLiteCommand created on a connection will (when
        executed) automatically join a transaction in progress, regardless of whether
        that transaction was created before or after the command.</p>
      <p>A SQLiteCommand object <b>can</b> be re-assigned a new SQLiteConnection object
        as long as no DataReaders are active on the command.</p>
      <p>Opening a transaction is considered a write operation, so only use them when
        you want to write to the database! If you hold open an &quot;immediate&quot;
        transaction, all readers on other connections will be blocked until the
        transaction is closed!</p>
      <p></p>
      <h4 class="subHeading">Thread Safety</h4>
      <p>Multi-threading in SQLite must be done carefully. Here are the restrictions:</p>
      <ul>
        <li>
          <b>You May</b>
        Clone() a SQLiteConnection object in one thread and pass the cloned object to
        another thread. Once passed, the other thread becomes the new owner of the
        cloned connection, and the original thread must not keep a reference to the
        clone or call any methods on the clone.
        <LI>
          <STRONG>You May</STRONG>
        create multiple threads, and those threads can create their own
        SQLiteConnection and subsequent objects for accessing a database.&nbsp;
        Multiple connections on multiple threads to the same database file are
        perfectly&nbsp;acceptable&nbsp;and will behave predictably.&nbsp;
        <li>
          <b>You May NOT</b>
        call methods or properties or otherwise reference any SQLite provider classes
        that belong to another thread.
        <li>
          <b>You May NOT</b> pass a SQLiteCommand, SQLiteDataReader, SQLiteDataAdapter or
          any other SQLite provider class except a cloned SQLiteConnection to another
          thread.</li>
      </ul>
      <p>Understand again that SQLite has no fine-grained locking mechanisms. It is
        therefore your own responsibility in a multi-threaded environment to handle
        potential timeouts that may occur if a long-running query in one thread
        prevents a query in another thread from executing. These timeouts will only
        occur if one thread is attempting to read while another thread is attempting to
        write. Whichever thread got its lock first will be the one to execute, and the
        other thread will block until the CommandTimeout value elapses or the other
        thread finishes.</p>
      <hr/>
      <div id="footer">
        <p>
          <a href="mailto:sqlite-users@sqlite.org?subject=SQLite.NET%20Class%20Library%20Documentation%20Feedback:%20Limitations">
            Send comments on this topic.</a>
        </p>