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diff --git a/www/session/rebaser.html b/www/session/rebaser.html new file mode 100644 index 0000000..7788f3d --- /dev/null +++ b/www/session/rebaser.html @@ -0,0 +1,217 @@ +<!DOCTYPE html> +<html><head> +<meta name="viewport" content="width=device-width, initial-scale=1.0"> +<meta http-equiv="content-type" content="text/html; charset=UTF-8"> +<link href="../sqlite.css" rel="stylesheet"> +<title>Rebasing changesets</title> +<!-- path=../ --> +</head> +<body> +<div class=nosearch> +<a href="../index.html"> +<img class="logo" src="../images/sqlite370_banner.gif" alt="SQLite" border="0"> +</a> +<div><!-- IE hack to prevent disappearing logo --></div> +<div class="tagline desktoponly"> +Small. Fast. 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And that +modifications are made that move that database to state S1 and a +changeset recorded (the "local" changeset). Then, a changeset based +on S0 is received from another site (the "remote" changeset) and +applied to the database. The database is then in state +(S1+"remote"), where the exact state depends on any conflict +resolution decisions (OMIT or REPLACE) made while applying "remote". +Rebasing a changeset is to update it to take those conflict +resolution decisions into account, so that the same conflicts +do not have to be resolved elsewhere in the network. </p> + +<p>For example, if both the local and remote changesets contain an +INSERT of the same key on "CREATE TABLE t1(a PRIMARY KEY, b)":</p> + +<p> local: INSERT INTO t1 VALUES(1, 'v1'); + remote: INSERT INTO t1 VALUES(1, 'v2');</p> + +<p>and the conflict resolution is REPLACE, then the INSERT change is +removed from the local changeset (it was overridden). Or, if the +conflict resolution was "OMIT", then the local changeset is modified +to instead contain:</p> + +<p> UPDATE t1 SET b = 'v2' WHERE a=1;</p> + +<p>Changes within the local changeset are rebased as follows:</p> + +<p><dl> +<dt>Local INSERT<dd> + This may only conflict with a remote INSERT. If the conflict + resolution was OMIT, then add an UPDATE change to the rebased + changeset. Or, if the conflict resolution was REPLACE, add + nothing to the rebased changeset.</p> + +<p><dt>Local DELETE<dd> + This may conflict with a remote UPDATE or DELETE. In both cases the + only possible resolution is OMIT. If the remote operation was a + DELETE, then add no change to the rebased changeset. If the remote + operation was an UPDATE, then the old.* fields of change are updated + to reflect the new.* values in the UPDATE.</p> + +<p><dt>Local UPDATE<dd> + This may conflict with a remote UPDATE or DELETE. If it conflicts + with a DELETE, and the conflict resolution was OMIT, then the update + is changed into an INSERT. Any undefined values in the new.* record + from the update change are filled in using the old.* values from + the conflicting DELETE. Or, if the conflict resolution was REPLACE, + the UPDATE change is simply omitted from the rebased changeset.</p> + +<p> If conflict is with a remote UPDATE and the resolution is OMIT, then + the old.* values are rebased using the new.* values in the remote + change. Or, if the resolution is REPLACE, then the change is copied + into the rebased changeset with updates to columns also updated by + the conflicting remote UPDATE removed. If this means no columns would + be updated, the change is omitted. +</dl></p> + +<p>A local change may be rebased against multiple remote changes +simultaneously. If a single key is modified by multiple remote +changesets, they are combined as follows before the local changeset +is rebased:</p> + +<p><ul> + <li> If there has been one or more REPLACE resolutions on a + key, it is rebased according to a REPLACE.</p> + +<p> <li> If there have been no REPLACE resolutions on a key, then + the local changeset is rebased according to the most recent + of the OMIT resolutions. +</ul></p> + +<p>Note that conflict resolutions from multiple remote changesets are +combined on a per-field basis, not per-row. This means that in the +case of multiple remote UPDATE operations, some fields of a single +local change may be rebased for REPLACE while others are rebased for +OMIT.</p> + +<p>In order to rebase a local changeset, the remote changeset must first +be applied to the local database using sqlite3changeset_apply_v2() and +the buffer of rebase information captured. Then:</p> + +<p><ol> + <li> An sqlite3_rebaser object is created by calling + sqlite3rebaser_create(). + <li> The new object is configured with the rebase buffer obtained from + sqlite3changeset_apply_v2() by calling sqlite3rebaser_configure(). + If the local changeset is to be rebased against multiple remote + changesets, then sqlite3rebaser_configure() should be called + multiple times, in the same order that the multiple + sqlite3changeset_apply_v2() calls were made. + <li> Each local changeset is rebased by calling sqlite3rebaser_rebase(). + <li> The sqlite3_rebaser object is deleted by calling + sqlite3rebaser_delete(). +</ol> +</p><p>See also lists of + <a href="objlist.html">Objects</a>, + <a href="constlist.html">Constants</a>, and + <a href="funclist.html">Functions</a>.</p> + |