From 18657a960e125336f704ea058e25c27bd3900dcb Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 5 May 2024 19:28:19 +0200 Subject: Adding upstream version 3.40.1. Signed-off-by: Daniel Baumann --- www/session/rebaser.html | 217 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 217 insertions(+) create mode 100644 www/session/rebaser.html (limited to 'www/session/rebaser.html') 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 @@ + + + + + +Rebasing changesets + + + +
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+Small. Fast. Reliable.
Choose any three. +
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Session Module C Interface

Rebasing changesets

typedef struct sqlite3_rebaser sqlite3_rebaser;
+

Important: This interface is experimental and is subject to change without notice.

+Suppose there is a site hosting a database in state S0. 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.

+ +

For example, if both the local and remote changesets contain an +INSERT of the same key on "CREATE TABLE t1(a PRIMARY KEY, b)":

+ +

local: INSERT INTO t1 VALUES(1, 'v1'); + remote: INSERT INTO t1 VALUES(1, 'v2');

+ +

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:

+ +

UPDATE t1 SET b = 'v2' WHERE a=1;

+ +

Changes within the local changeset are rebased as follows:

+ +

+
Local INSERT
+ 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.

+ +

Local DELETE
+ 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.

+ +

Local UPDATE
+ 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.

+ +

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. +

+ +

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:

+ +

+ +

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.

+ +

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:

+ +

    +
  1. An sqlite3_rebaser object is created by calling + sqlite3rebaser_create(). +
  2. 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. +
  3. Each local changeset is rebased by calling sqlite3rebaser_rebase(). +
  4. The sqlite3_rebaser object is deleted by calling + sqlite3rebaser_delete(). +
+

See also lists of + Objects, + Constants, and + Functions.

+ -- cgit v1.2.3