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Commit67b9b3c

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Provide XLogRecGetFullXid().
In order to be able to work with FullTransactionId values during replaywithout increasing the size of the WAL, infer the epoch. In general wecan't do that safely, but during replay we can because we know thatnextFullXid can't advance concurrently.Prevent frontend code from seeing this new function, due to the aboverestriction. Perhaps in future it will be possible to extract the valueentirely from independent WAL records, and then this restriction can belifted.Author: Thomas Munro, based on earlier code from Andres FreundDiscussion:https://postgr.es/m/CA%2BhUKG%2BmLmuDjMi6o1dxkKvGRL56Y2Rz%2BiXAcrZV03G9ZuFQ8Q%40mail.gmail.com
1 parent5925e55 commit67b9b3c

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‎src/backend/access/transam/xlogreader.c

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@@ -26,6 +26,7 @@
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#include"replication/origin.h"
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#ifndefFRONTEND
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#include"miscadmin.h"
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#include"utils/memutils.h"
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#endif
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@@ -1443,3 +1444,37 @@ RestoreBlockImage(XLogReaderState *record, uint8 block_id, char *page)
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return true;
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}
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#ifndefFRONTEND
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/*
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* Extract the FullTransactionId from a WAL record.
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*/
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FullTransactionId
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XLogRecGetFullXid(XLogReaderState*record)
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{
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TransactionIdxid,
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next_xid;
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uint32epoch;
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/*
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* This function is only safe during replay, because it depends on the
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* replay state. See AdvanceNextFullTransactionIdPastXid() for more.
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*/
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Assert(AmStartupProcess()|| !IsUnderPostmaster);
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xid=XLogRecGetXid(record);
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next_xid=XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
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epoch=EpochFromFullTransactionId(ShmemVariableCache->nextFullXid);
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/*
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* If xid is numerically greater than next_xid, it has to be from the
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* last epoch.
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*/
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if (unlikely(xid>next_xid))
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--epoch;
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returnFullTransactionIdFromEpochAndXid(epoch,xid);
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};
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#endif

‎src/include/access/xlogreader.h

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#ifndefXLOGREADER_H
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#defineXLOGREADER_H
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#ifndefFRONTEND
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#include"access/transam.h"
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#endif
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#include"access/xlogrecord.h"
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typedefstructXLogReaderStateXLogReaderState;
@@ -240,6 +244,10 @@ extern bool DecodeXLogRecord(XLogReaderState *state, XLogRecord *record,
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#defineXLogRecBlockImageApply(decoder,block_id) \
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((decoder)->blocks[block_id].apply_image)
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#ifndefFRONTEND
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externFullTransactionIdXLogRecGetFullXid(XLogReaderState*record);
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#endif
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externboolRestoreBlockImage(XLogReaderState*recoder,uint8block_id,char*dst);
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externchar*XLogRecGetBlockData(XLogReaderState*record,uint8block_id,Size*len);
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externboolXLogRecGetBlockTag(XLogReaderState*record,uint8block_id,

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