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Commit766571b

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Additional write barrier in AdvanceXLInsertBuffer().
First, mark the xlblocks member with InvalidXLogRecPtr, then issue awrite barrier, then initialize it. That ensures that the xlblocksmember doesn't appear valid while the contents are being initialized.In preparation for reading WAL buffer contents without a lock.Author: Bharath RupireddyDiscussion:https://postgr.es/m/CALj2ACVfFMfqD5oLzZSQQZWfXiJqd-NdX0_317veP6FuB31QWA@mail.gmail.comReviewed-by: Andres Freund
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  • src/backend/access/transam

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‎src/backend/access/transam/xlog.c

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@@ -1932,6 +1932,14 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
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NewPage= (XLogPageHeader) (XLogCtl->pages+nextidx* (Size)XLOG_BLCKSZ);
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/*
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* Mark the xlblock with InvalidXLogRecPtr and issue a write barrier
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* before initializing. Otherwise, the old page may be partially
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* zeroed but look valid.
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*/
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pg_atomic_write_u64(&XLogCtl->xlblocks[nextidx],InvalidXLogRecPtr);
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pg_write_barrier();
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/*
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* Be sure to re-zero the buffer so that bytes beyond what we've
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* written will look like zeroes and not valid XLOG records...

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