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* Log rows in online_alter_binlog. * Table online data is replicated within dedicated binlog file * Cached data is written on commit. * Versioning is fully supported. * Works both wit and without binlog enabled. * For now savepoints setup is forbidden while ONLINE ALTER goes on. Extra support is required. We can simply log the SAVEPOINT query events and replicate them together with row events. But it's not implemented for now. * Cache flipping: We want to care for the possible bottleneck in the online alter binlog reading/writing in advance. IO_CACHE does not provide anything better that sequential access, besides, only a single write is mutex-protected, which is not suitable, since we should write a transaction atomically. To solve this, a special layer on top Event_log is implemented. There are two IO_CACHE files underneath: one for reading, and one for writing. Once the read cache is empty, an exclusive lock is acquired (we can wait for a currently active transaction finish writing), and flip() is emitted, i.e. the write cache is reopened for read, and the read cache is emptied, and reopened for writing. This reminds a buffer flip that happens in accelerated graphics (DirectX/OpenGL/etc). Cache_flip_event_log is considered non-blocking for a single reader and a single writer in this sense, with the only lock held by reader during flip. An alternative approach by implementing a fair concurrent circular buffer is described in MDEV-24676. * Cache managers: We have two cache sinks: statement and transactional. It is important that the changes are first cached per-statement and per-transaction. If a statement fails, then only statement data is rolled back. The transaction moves along, however. Turns out, there's no guarantee that TABLE well persist in thd->open_tables to the transaction commit moment. If an error occurs, tables from statement are purged. Therefore, we can't store te caches in TABLE. Ideally, it should be handlerton, but we cut the corner and store it in THD in a list.
33 lines
1,000 B
Text
33 lines
1,000 B
Text
SET @odl_sync_frm = @@global.sync_frm;
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SET @@global.sync_frm = OFF;
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connect locker,localhost,root,,;
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connect writer,localhost,root,,;
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connection default;
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DROP TABLE IF EXISTS t1;
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CREATE TABLE t1( a INT, b INT );
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CREATE TABLE t2( a INT, b INT );
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INSERT INTO t1 VALUES (1, 1), (2, 2), (3, 3), (4, 4);
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INSERT INTO t2 VALUES (1, 1), (2, 2), (3, 3), (4, 4);
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# 1. test regular tables
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# 1.1. test altering of columns that multiupdate doesn't use
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# 1.1.1. normal mode
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# 1.1.2. PS mode
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# 1.2. test altering of columns that multiupdate uses
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# 1.2.1. normal mode
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connection default;
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# 1.2.2. PS mode
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connection default;
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ALTER TABLE t1 ADD COLUMN a INT, LOCK=SHARED;
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# 2. test UNIONs
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# 2.1. test altering of columns that multiupdate doesn't use
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# 2.1.1. normal mode
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# 2.1.2. PS mode
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# 2.2. test altering of columns that multiupdate uses
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# 2.2.1. normal mode
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connection default;
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# 2.2.2. PS mode
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connection default;
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DROP TABLE t1,t2;
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disconnect locker;
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disconnect writer;
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SET @@global.sync_frm = @odl_sync_frm;
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