MySQL: why undo log is required in the processes of database recovery?
Let's imagine that an incident happens when you updates.
start transaction;
update users set gender = 1 where id = 3;
- Undo log space is allocated.
- Previous values are copied to undo log
- Record of undo log modifications are written to redo log.
- page is modified in buffer pull.
- Record of page modification are written to redo log, and this page is marked as dirty.
- then, an incident happen, MySQL crashes!
we restart MySQL, then recover from an incident, there are three steps:
- Analysis
- Redo, which will restore the state when MySQL crashed.
- Undo.
For step3, we are undo uncommitted transactions through undo log in backwards order.
My questions are:
Can we do step3 by undo
redo logthat caused by uncommitted transaction, rather than applyundo log?Why
undo logis required in the step3?Is undo log for
recover from an crash that happens within recovery?
mysql transaction-log transaction recovery
asked 15 mins ago
Ryan LvRyan Lv
6318
add a comment |
Let's imagine that an incident happens when you updates.
start transaction;
update users set gender = 1 where id = 3;
- Undo log space is allocated.
- Previous values are copied to undo log
- Record of undo log modifications are written to redo log.
- page is modified in buffer pull.
- Record of page modification are written to redo log, and this page is marked as dirty.
- then, an incident happen, MySQL crashes!
we restart MySQL, then recover from an incident, there are three steps:
- Analysis
- Redo, which will restore the state when MySQL crashed.
- Undo.
For step3, we are undo uncommitted transactions through undo log in backwards order.
My questions are:
Can we do step3 by undo
redo logthat caused by uncommitted transaction, rather than applyundo log?Why
undo logis required in the step3?Is undo log for
recover from an crash that happens within recovery?
mysql transaction-log transaction recovery
asked 15 mins ago
Ryan LvRyan Lv
6318
add a comment |
Let's imagine that an incident happens when you updates.
start transaction;
update users set gender = 1 where id = 3;
- Undo log space is allocated.
- Previous values are copied to undo log
- Record of undo log modifications are written to redo log.
- page is modified in buffer pull.
- Record of page modification are written to redo log, and this page is marked as dirty.
- then, an incident happen, MySQL crashes!
we restart MySQL, then recover from an incident, there are three steps:
- Analysis
- Redo, which will restore the state when MySQL crashed.
- Undo.
For step3, we are undo uncommitted transactions through undo log in backwards order.
My questions are:
Can we do step3 by undo
redo logthat caused by uncommitted transaction, rather than applyundo log?Why
undo logis required in the step3?Is undo log for
recover from an crash that happens within recovery?
mysql transaction-log transaction recovery
asked 15 mins ago
Ryan LvRyan Lv
6318
Let's imagine that an incident happens when you updates.
start transaction;
update users set gender = 1 where id = 3;
- Undo log space is allocated.
- Previous values are copied to undo log
- Record of undo log modifications are written to redo log.
- page is modified in buffer pull.
- Record of page modification are written to redo log, and this page is marked as dirty.
- then, an incident happen, MySQL crashes!
we restart MySQL, then recover from an incident, there are three steps:
- Analysis
- Redo, which will restore the state when MySQL crashed.
- Undo.
For step3, we are undo uncommitted transactions through undo log in backwards order.
My questions are:
Can we do step3 by undo
redo logthat caused by uncommitted transaction, rather than applyundo log?Why
undo logis required in the step3?Is undo log for
recover from an crash that happens within recovery?
mysql transaction-log transaction recovery
mysql transaction-log transaction recovery
asked 15 mins ago
Ryan LvRyan Lv
6318
asked 15 mins ago
Ryan LvRyan Lv
6318
edited 1 min ago
Ryan Lv
asked 15 mins ago
Ryan LvRyan Lv
6318
asked 15 mins ago
Ryan LvRyan Lv
6318
asked 15 mins ago
Ryan LvRyan Lv
6318
6318
add a comment |
add a comment |
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