Optimization for hot standby XLOG_STANDBY_LOCK redo
| От | 邱宇航 |
|---|---|
| Тема | Optimization for hot standby XLOG_STANDBY_LOCK redo |
| Дата | |
| Msg-id | 2403B554-09D6-4006-9A1F-866E2E6BEF46@gmail.com обсуждение исходный текст |
| Ответы |
Re: Optimization for hot standby XLOG_STANDBY_LOCK redo
|
| Список | pgsql-hackers |
I noticed that in hot standby, XLOG_STANDBY_LOCK redo is sometimes block by another query, and all the rest redo is blocked by this lock getting operation, which is not good and often happed in my database, so the hot standby will be left behind and master will store a lot of WAL which can’t be purged.
standby_redo
So here is the idea:
We can do XLOG_STANDBY_LOCK redo asynchronously, and the rest redo will continue.
And I wonder will LogStandbySnapshot influence the consistency in hot standby, for the redo is not by order. And how to avoid this.
// ------ startup ------
StartupXLOG()
StartupXLOG()
{
while (readRecord())
{
check_lock_get_state(); if (record.tx is in pending tbl):
append this record to the pending lock for further redo.
redo_record();
}
}
check_lock_get_state()
{
for (tx in pending_tx):
if (tx.all_lock are got):
redo the rest record for this tx
free this tx
}
standby_redo
{
if (XLOG_STANDBY_LOCK redo falied)
// ------ worker process ------
if (XLOG_STANDBY_LOCK redo falied)
{
add_lock_to_pending_tx_tbl(); }
}
// ------ worker process ------
main()
{
while(true)
{
for (lock in pending locks order by lsn)
try_to_get_lock_from_pending_tbl(); }
}
regards.
Yuhang
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