462 lines
20 KiB
C
462 lines
20 KiB
C
/*
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** 2014 August 30
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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**
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** This file contains the public interface for the RBU extension.
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*/
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/*
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** SUMMARY
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**
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** Writing a transaction containing a large number of operations on
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** b-tree indexes that are collectively larger than the available cache
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** memory can be very inefficient.
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**
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** The problem is that in order to update a b-tree, the leaf page (at least)
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** containing the entry being inserted or deleted must be modified. If the
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** working set of leaves is larger than the available cache memory, then a
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** single leaf that is modified more than once as part of the transaction
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** may be loaded from or written to the persistent media multiple times.
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** Additionally, because the index updates are likely to be applied in
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** random order, access to pages within the database is also likely to be in
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** random order, which is itself quite inefficient.
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**
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** One way to improve the situation is to sort the operations on each index
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** by index key before applying them to the b-tree. This leads to an IO
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** pattern that resembles a single linear scan through the index b-tree,
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** and all but guarantees each modified leaf page is loaded and stored
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** exactly once. SQLite uses this trick to improve the performance of
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** CREATE INDEX commands. This extension allows it to be used to improve
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** the performance of large transactions on existing databases.
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**
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** Additionally, this extension allows the work involved in writing the
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** large transaction to be broken down into sub-transactions performed
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** sequentially by separate processes. This is useful if the system cannot
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** guarantee that a single update process will run for long enough to apply
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** the entire update, for example because the update is being applied on a
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** mobile device that is frequently rebooted. Even after the writer process
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** has committed one or more sub-transactions, other database clients continue
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** to read from the original database snapshot. In other words, partially
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** applied transactions are not visible to other clients.
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**
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** "RBU" stands for "Resumable Bulk Update". As in a large database update
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** transmitted via a wireless network to a mobile device. A transaction
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** applied using this extension is hence refered to as an "RBU update".
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**
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**
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** LIMITATIONS
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**
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** An "RBU update" transaction is subject to the following limitations:
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**
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** * The transaction must consist of INSERT, UPDATE and DELETE operations
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** only.
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**
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** * INSERT statements may not use any default values.
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**
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** * UPDATE and DELETE statements must identify their target rows by
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** non-NULL PRIMARY KEY values. Rows with NULL values stored in PRIMARY
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** KEY fields may not be updated or deleted. If the table being written
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** has no PRIMARY KEY, affected rows must be identified by rowid.
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**
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** * UPDATE statements may not modify PRIMARY KEY columns.
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**
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** * No triggers will be fired.
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**
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** * No foreign key violations are detected or reported.
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**
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** * CHECK constraints are not enforced.
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**
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** * No constraint handling mode except for "OR ROLLBACK" is supported.
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**
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**
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** PREPARATION
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**
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** An "RBU update" is stored as a separate SQLite database. A database
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** containing an RBU update is an "RBU database". For each table in the
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** target database to be updated, the RBU database should contain a table
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** named "data_<target name>" containing the same set of columns as the
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** target table, and one more - "rbu_control". The data_% table should
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** have no PRIMARY KEY or UNIQUE constraints, but each column should have
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** the same type as the corresponding column in the target database.
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** The "rbu_control" column should have no type at all. For example, if
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** the target database contains:
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**
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** CREATE TABLE t1(a INTEGER PRIMARY KEY, b TEXT, c UNIQUE);
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**
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** Then the RBU database should contain:
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**
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** CREATE TABLE data_t1(a INTEGER, b TEXT, c, rbu_control);
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**
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** The order of the columns in the data_% table does not matter.
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**
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** Instead of a regular table, the RBU database may also contain virtual
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** tables or view named using the data_<target> naming scheme.
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**
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** Instead of the plain data_<target> naming scheme, RBU database tables
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** may also be named data<integer>_<target>, where <integer> is any sequence
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** of zero or more numeric characters (0-9). This can be significant because
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** tables within the RBU database are always processed in order sorted by
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** name. By judicious selection of the the <integer> portion of the names
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** of the RBU tables the user can therefore control the order in which they
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** are processed. This can be useful, for example, to ensure that "external
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** content" FTS4 tables are updated before their underlying content tables.
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**
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** If the target database table is a virtual table or a table that has no
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** PRIMARY KEY declaration, the data_% table must also contain a column
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** named "rbu_rowid". This column is mapped to the tables implicit primary
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** key column - "rowid". Virtual tables for which the "rowid" column does
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** not function like a primary key value cannot be updated using RBU. For
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** example, if the target db contains either of the following:
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**
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** CREATE VIRTUAL TABLE x1 USING fts3(a, b);
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** CREATE TABLE x1(a, b)
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**
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** then the RBU database should contain:
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**
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** CREATE TABLE data_x1(a, b, rbu_rowid, rbu_control);
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**
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** All non-hidden columns (i.e. all columns matched by "SELECT *") of the
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** target table must be present in the input table. For virtual tables,
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** hidden columns are optional - they are updated by RBU if present in
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** the input table, or not otherwise. For example, to write to an fts4
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** table with a hidden languageid column such as:
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**
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** CREATE VIRTUAL TABLE ft1 USING fts4(a, b, languageid='langid');
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**
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** Either of the following input table schemas may be used:
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**
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** CREATE TABLE data_ft1(a, b, langid, rbu_rowid, rbu_control);
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** CREATE TABLE data_ft1(a, b, rbu_rowid, rbu_control);
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**
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** For each row to INSERT into the target database as part of the RBU
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** update, the corresponding data_% table should contain a single record
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** with the "rbu_control" column set to contain integer value 0. The
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** other columns should be set to the values that make up the new record
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** to insert.
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**
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** If the target database table has an INTEGER PRIMARY KEY, it is not
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** possible to insert a NULL value into the IPK column. Attempting to
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** do so results in an SQLITE_MISMATCH error.
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**
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** For each row to DELETE from the target database as part of the RBU
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** update, the corresponding data_% table should contain a single record
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** with the "rbu_control" column set to contain integer value 1. The
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** real primary key values of the row to delete should be stored in the
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** corresponding columns of the data_% table. The values stored in the
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** other columns are not used.
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**
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** For each row to UPDATE from the target database as part of the RBU
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** update, the corresponding data_% table should contain a single record
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** with the "rbu_control" column set to contain a value of type text.
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** The real primary key values identifying the row to update should be
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** stored in the corresponding columns of the data_% table row, as should
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** the new values of all columns being update. The text value in the
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** "rbu_control" column must contain the same number of characters as
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** there are columns in the target database table, and must consist entirely
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** of 'x' and '.' characters (or in some special cases 'd' - see below). For
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** each column that is being updated, the corresponding character is set to
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** 'x'. For those that remain as they are, the corresponding character of the
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** rbu_control value should be set to '.'. For example, given the tables
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** above, the update statement:
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**
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** UPDATE t1 SET c = 'usa' WHERE a = 4;
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**
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** is represented by the data_t1 row created by:
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**
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** INSERT INTO data_t1(a, b, c, rbu_control) VALUES(4, NULL, 'usa', '..x');
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**
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** Instead of an 'x' character, characters of the rbu_control value specified
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** for UPDATEs may also be set to 'd'. In this case, instead of updating the
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** target table with the value stored in the corresponding data_% column, the
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** user-defined SQL function "rbu_delta()" is invoked and the result stored in
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** the target table column. rbu_delta() is invoked with two arguments - the
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** original value currently stored in the target table column and the
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** value specified in the data_xxx table.
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**
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** For example, this row:
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**
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** INSERT INTO data_t1(a, b, c, rbu_control) VALUES(4, NULL, 'usa', '..d');
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**
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** is similar to an UPDATE statement such as:
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**
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** UPDATE t1 SET c = rbu_delta(c, 'usa') WHERE a = 4;
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**
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** Finally, if an 'f' character appears in place of a 'd' or 's' in an
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** ota_control string, the contents of the data_xxx table column is assumed
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** to be a "fossil delta" - a patch to be applied to a blob value in the
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** format used by the fossil source-code management system. In this case
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** the existing value within the target database table must be of type BLOB.
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** It is replaced by the result of applying the specified fossil delta to
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** itself.
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**
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** If the target database table is a virtual table or a table with no PRIMARY
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** KEY, the rbu_control value should not include a character corresponding
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** to the rbu_rowid value. For example, this:
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**
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** INSERT INTO data_ft1(a, b, rbu_rowid, rbu_control)
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** VALUES(NULL, 'usa', 12, '.x');
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**
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** causes a result similar to:
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**
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** UPDATE ft1 SET b = 'usa' WHERE rowid = 12;
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**
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** The data_xxx tables themselves should have no PRIMARY KEY declarations.
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** However, RBU is more efficient if reading the rows in from each data_xxx
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** table in "rowid" order is roughly the same as reading them sorted by
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** the PRIMARY KEY of the corresponding target database table. In other
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** words, rows should be sorted using the destination table PRIMARY KEY
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** fields before they are inserted into the data_xxx tables.
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**
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** USAGE
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**
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** The API declared below allows an application to apply an RBU update
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** stored on disk to an existing target database. Essentially, the
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** application:
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**
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** 1) Opens an RBU handle using the sqlite3rbu_open() function.
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**
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** 2) Registers any required virtual table modules with the database
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** handle returned by sqlite3rbu_db(). Also, if required, register
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** the rbu_delta() implementation.
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**
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** 3) Calls the sqlite3rbu_step() function one or more times on
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** the new handle. Each call to sqlite3rbu_step() performs a single
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** b-tree operation, so thousands of calls may be required to apply
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** a complete update.
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**
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** 4) Calls sqlite3rbu_close() to close the RBU update handle. If
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** sqlite3rbu_step() has been called enough times to completely
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** apply the update to the target database, then the RBU database
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** is marked as fully applied. Otherwise, the state of the RBU
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** update application is saved in the RBU database for later
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** resumption.
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**
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** See comments below for more detail on APIs.
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**
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** If an update is only partially applied to the target database by the
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** time sqlite3rbu_close() is called, various state information is saved
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** within the RBU database. This allows subsequent processes to automatically
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** resume the RBU update from where it left off.
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**
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** To remove all RBU extension state information, returning an RBU database
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** to its original contents, it is sufficient to drop all tables that begin
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** with the prefix "rbu_"
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**
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** DATABASE LOCKING
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**
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** An RBU update may not be applied to a database in WAL mode. Attempting
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** to do so is an error (SQLITE_ERROR).
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**
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** While an RBU handle is open, a SHARED lock may be held on the target
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** database file. This means it is possible for other clients to read the
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** database, but not to write it.
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**
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** If an RBU update is started and then suspended before it is completed,
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** then an external client writes to the database, then attempting to resume
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** the suspended RBU update is also an error (SQLITE_BUSY).
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*/
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#ifndef _SQLITE3RBU_H
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#define _SQLITE3RBU_H
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#include "sqlite3.h" /* Required for error code definitions */
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#ifdef __cplusplus
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extern "C" {
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#endif
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typedef struct sqlite3rbu sqlite3rbu;
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/*
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** Open an RBU handle.
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**
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** Argument zTarget is the path to the target database. Argument zRbu is
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** the path to the RBU database. Each call to this function must be matched
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** by a call to sqlite3rbu_close(). When opening the databases, RBU passes
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** the SQLITE_CONFIG_URI flag to sqlite3_open_v2(). So if either zTarget
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** or zRbu begin with "file:", it will be interpreted as an SQLite
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** database URI, not a regular file name.
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**
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** If the zState argument is passed a NULL value, the RBU extension stores
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** the current state of the update (how many rows have been updated, which
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** indexes are yet to be updated etc.) within the RBU database itself. This
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** can be convenient, as it means that the RBU application does not need to
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** organize removing a separate state file after the update is concluded.
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** Or, if zState is non-NULL, it must be a path to a database file in which
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** the RBU extension can store the state of the update.
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**
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** When resuming an RBU update, the zState argument must be passed the same
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** value as when the RBU update was started.
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**
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** Once the RBU update is finished, the RBU extension does not
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** automatically remove any zState database file, even if it created it.
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**
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** By default, RBU uses the default VFS to access the files on disk. To
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** use a VFS other than the default, an SQLite "file:" URI containing a
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** "vfs=..." option may be passed as the zTarget option.
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**
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** IMPORTANT NOTE FOR ZIPVFS USERS: The RBU extension works with all of
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** SQLite's built-in VFSs, including the multiplexor VFS. However it does
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** not work out of the box with zipvfs. Refer to the comment describing
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** the zipvfs_create_vfs() API below for details on using RBU with zipvfs.
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*/
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sqlite3rbu *sqlite3rbu_open(
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const char *zTarget,
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const char *zRbu,
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const char *zState
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);
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/*
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** Internally, each RBU connection uses a separate SQLite database
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** connection to access the target and rbu update databases. This
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** API allows the application direct access to these database handles.
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**
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** The first argument passed to this function must be a valid, open, RBU
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** handle. The second argument should be passed zero to access the target
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** database handle, or non-zero to access the rbu update database handle.
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** Accessing the underlying database handles may be useful in the
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** following scenarios:
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**
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** * If any target tables are virtual tables, it may be necessary to
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** call sqlite3_create_module() on the target database handle to
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** register the required virtual table implementations.
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**
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** * If the data_xxx tables in the RBU source database are virtual
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** tables, the application may need to call sqlite3_create_module() on
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** the rbu update db handle to any required virtual table
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** implementations.
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**
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** * If the application uses the "rbu_delta()" feature described above,
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** it must use sqlite3_create_function() or similar to register the
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** rbu_delta() implementation with the target database handle.
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**
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** If an error has occurred, either while opening or stepping the RBU object,
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** this function may return NULL. The error code and message may be collected
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** when sqlite3rbu_close() is called.
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**
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** Database handles returned by this function remain valid until the next
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** call to any sqlite3rbu_xxx() function other than sqlite3rbu_db().
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*/
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sqlite3 *sqlite3rbu_db(sqlite3rbu*, int bRbu);
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/*
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** Do some work towards applying the RBU update to the target db.
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**
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** Return SQLITE_DONE if the update has been completely applied, or
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** SQLITE_OK if no error occurs but there remains work to do to apply
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** the RBU update. If an error does occur, some other error code is
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** returned.
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**
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** Once a call to sqlite3rbu_step() has returned a value other than
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** SQLITE_OK, all subsequent calls on the same RBU handle are no-ops
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** that immediately return the same value.
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*/
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int sqlite3rbu_step(sqlite3rbu *pRbu);
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/*
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** Force RBU to save its state to disk.
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**
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** If a power failure or application crash occurs during an update, following
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** system recovery RBU may resume the update from the point at which the state
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** was last saved. In other words, from the most recent successful call to
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** sqlite3rbu_close() or this function.
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**
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** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
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*/
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int sqlite3rbu_savestate(sqlite3rbu *pRbu);
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/*
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** Close an RBU handle.
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**
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** If the RBU update has been completely applied, mark the RBU database
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** as fully applied. Otherwise, assuming no error has occurred, save the
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** current state of the RBU update appliation to the RBU database.
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**
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** If an error has already occurred as part of an sqlite3rbu_step()
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** or sqlite3rbu_open() call, or if one occurs within this function, an
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** SQLite error code is returned. Additionally, *pzErrmsg may be set to
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** point to a buffer containing a utf-8 formatted English language error
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** message. It is the responsibility of the caller to eventually free any
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** such buffer using sqlite3_free().
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**
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** Otherwise, if no error occurs, this function returns SQLITE_OK if the
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** update has been partially applied, or SQLITE_DONE if it has been
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** completely applied.
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*/
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int sqlite3rbu_close(sqlite3rbu *pRbu, char **pzErrmsg);
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/*
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** Return the total number of key-value operations (inserts, deletes or
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** updates) that have been performed on the target database since the
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** current RBU update was started.
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*/
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sqlite3_int64 sqlite3rbu_progress(sqlite3rbu *pRbu);
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/*
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** Create an RBU VFS named zName that accesses the underlying file-system
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** via existing VFS zParent. Or, if the zParent parameter is passed NULL,
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** then the new RBU VFS uses the default system VFS to access the file-system.
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** The new object is registered as a non-default VFS with SQLite before
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** returning.
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**
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** Part of the RBU implementation uses a custom VFS object. Usually, this
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** object is created and deleted automatically by RBU.
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**
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** The exception is for applications that also use zipvfs. In this case,
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** the custom VFS must be explicitly created by the user before the RBU
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** handle is opened. The RBU VFS should be installed so that the zipvfs
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** VFS uses the RBU VFS, which in turn uses any other VFS layers in use
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** (for example multiplexor) to access the file-system. For example,
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** to assemble an RBU enabled VFS stack that uses both zipvfs and
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** multiplexor (error checking omitted):
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**
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** // Create a VFS named "multiplex" (not the default).
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** sqlite3_multiplex_initialize(0, 0);
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**
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** // Create an rbu VFS named "rbu" that uses multiplexor. If the
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** // second argument were replaced with NULL, the "rbu" VFS would
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** // access the file-system via the system default VFS, bypassing the
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** // multiplexor.
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** sqlite3rbu_create_vfs("rbu", "multiplex");
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**
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** // Create a zipvfs VFS named "zipvfs" that uses rbu.
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** zipvfs_create_vfs_v3("zipvfs", "rbu", 0, xCompressorAlgorithmDetector);
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**
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** // Make zipvfs the default VFS.
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** sqlite3_vfs_register(sqlite3_vfs_find("zipvfs"), 1);
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**
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** Because the default VFS created above includes a RBU functionality, it
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** may be used by RBU clients. Attempting to use RBU with a zipvfs VFS stack
|
|
** that does not include the RBU layer results in an error.
|
|
**
|
|
** The overhead of adding the "rbu" VFS to the system is negligible for
|
|
** non-RBU users. There is no harm in an application accessing the
|
|
** file-system via "rbu" all the time, even if it only uses RBU functionality
|
|
** occasionally.
|
|
*/
|
|
int sqlite3rbu_create_vfs(const char *zName, const char *zParent);
|
|
|
|
/*
|
|
** Deregister and destroy an RBU vfs created by an earlier call to
|
|
** sqlite3rbu_create_vfs().
|
|
**
|
|
** VFS objects are not reference counted. If a VFS object is destroyed
|
|
** before all database handles that use it have been closed, the results
|
|
** are undefined.
|
|
*/
|
|
void sqlite3rbu_destroy_vfs(const char *zName);
|
|
|
|
#ifdef __cplusplus
|
|
} /* end of the 'extern "C"' block */
|
|
#endif
|
|
|
|
#endif /* _SQLITE3RBU_H */
|