MDEV-12353: Reduce log volume by an UNDO_INIT record

We introduce an EXTENDED log record for initializing an undo log page.
The size of the record will be 2 bytes plus the optional page identifier.
The entire undo page will be initialized, except the space that is
already reserved for TRX_UNDO_SEG_HDR in trx_undo_seg_create().

mtr_t::undo_create(): Write the UNDO_INIT record.

trx_undo_page_init(): Initialize the undo page corresponding to the
UNDO_INIT record. Unlike the former MLOG_UNDO_INIT record, we will
initialize almost the entire page, including initializing the
TRX_UNDO_PAGE_NODE to an empty list node, so that the subsequent call
to flst_init() will avoid writing log for the undo page.

1 files changed, 7 insertions, 0 deletions

diff --git a/storage/innobase/include/trx0undo.h b/storage/innobase/include/trx0undo.h
index b68f34ff4da..37421930b9b 100644
--- a/storage/innobase/include/trx0undo.h
+++ b/storage/innobase/include/trx0undo.h
@@ -156,6 +156,13 @@ trx_undo_get_first_rec(const fil_space_t &space, uint32_t page_no,
                        uint16_t offset, ulint mode, buf_block_t*& block,
                        mtr_t *mtr);
 
+/** Initialize an undo log page.
+NOTE: This corresponds to a redo log record and must not be changed!
+@see mtr_t::undo_create()
+@param[in,out]	block	undo log page */
+void trx_undo_page_init(const buf_block_t &block)
+	MY_ATTRIBUTE((nonnull));
+
 /** Allocate an undo log page.
 @param[in,out]	undo	undo log
 @param[in,out]	mtr	mini-transaction that does not hold any page latch