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Comment:Fix typos on the wal.html page.
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SHA1: 3bf3e14239c269dbefe6fc88f1bc64ea690297d9
User & Date: drh 2010-06-25 13:45:43
Context
2010-06-25
14:52
Add the ability to include TEA snapshots on the download page. check-in: 2415d6de49 user: drh tags: trunk
13:45
Fix typos on the wal.html page. check-in: 3bf3e14239 user: drh tags: trunk
2010-06-24
17:51
Improve explanation of page_size limitations in WAL mode. Fix a broken link in fileformat2.in. check-in: c079123bb9 user: drh tags: trunk
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revert the database file to its original state.  The [COMMIT] occurs
when the rollback journal is deleted.</p>

<p>The WAL approach inverts this.  The original content is preserved
in the database file and the changes are appended into a separate
WAL file.  A [COMMIT] occurs when a special record indicating a commit
is appended to the WAL.  Thus a COMMIT can happen without ever writing
to the original database, which allows reader to continue operating
from the original unaltered database while changes are simultaneously being
committed into the WAL.  Multiple transactions can be appended to the
end of a single WAL file.</p>

<tcl>hd_fragment ckpt checkpoint checkpointed checkpointing</tcl>
<h3>Checkpointing</h3>

................................................................................
<p>The journal_mode pragma returns a string which is the new journal mode.
On success, the pragma will return the string "<tt>wal</tt>".  If 
the conversion to WAL could not be completed (for example, if the VFS
does not support the necessary shared-memory primitives) then the
journaling mode will be unchanged and the string returned from the
primitive will be the prior journaling mode (for example "<tt>delete</tt>").

<a name="how_to_checkpoint">
<p>By default, SQLite will automatically checkpoint whenever a [COMMIT]
occurs that causes the WAL file to be 1000 pages or more in size, or when the 
last database connection on a database file closes.  The default 
configuration is intended to work well for most applications.
But programs that want more control can force a checkpoint
using the [wal_checkpoint pragma] or by calling the
[sqlite3_wal_checkpoint()] C interface.  The automatic checkpoint







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revert the database file to its original state.  The [COMMIT] occurs
when the rollback journal is deleted.</p>

<p>The WAL approach inverts this.  The original content is preserved
in the database file and the changes are appended into a separate
WAL file.  A [COMMIT] occurs when a special record indicating a commit
is appended to the WAL.  Thus a COMMIT can happen without ever writing
to the original database, which allows readers to continue operating
from the original unaltered database while changes are simultaneously being
committed into the WAL.  Multiple transactions can be appended to the
end of a single WAL file.</p>

<tcl>hd_fragment ckpt checkpoint checkpointed checkpointing</tcl>
<h3>Checkpointing</h3>

................................................................................
<p>The journal_mode pragma returns a string which is the new journal mode.
On success, the pragma will return the string "<tt>wal</tt>".  If 
the conversion to WAL could not be completed (for example, if the VFS
does not support the necessary shared-memory primitives) then the
journaling mode will be unchanged and the string returned from the
primitive will be the prior journaling mode (for example "<tt>delete</tt>").

<a name="how_to_checkpoint"></a>
<p>By default, SQLite will automatically checkpoint whenever a [COMMIT]
occurs that causes the WAL file to be 1000 pages or more in size, or when the 
last database connection on a database file closes.  The default 
configuration is intended to work well for most applications.
But programs that want more control can force a checkpoint
using the [wal_checkpoint pragma] or by calling the
[sqlite3_wal_checkpoint()] C interface.  The automatic checkpoint