From 92235f7ceebc92dc6ce36b97c0843fc514a96e01 Mon Sep 17 00:00:00 2001
From: xiong_xjun <xiong_xiaojun@yeah.net>
Date: Wed, 19 Aug 2020 14:51:50 +0800
Subject: [PATCH] consider vacuum's xmin when truncate csnlog in checkpoint

---
 .../storage/access/transam/xlog.cpp           | 10 ++++--
 src/gausskernel/storage/ipc/procarray.cpp     | 35 +++++++++++++++----
 src/include/storage/procarray.h               |  2 +-
 3 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/src/gausskernel/storage/access/transam/xlog.cpp b/src/gausskernel/storage/access/transam/xlog.cpp
index f8d5415c5d..10ca376be0 100755
--- a/src/gausskernel/storage/access/transam/xlog.cpp
+++ b/src/gausskernel/storage/access/transam/xlog.cpp
@@ -9975,6 +9975,7 @@ void CreateCheckPoint(int flags)
     XLogRecPtr curMinRecLSN = InvalidXLogRecPtr;
     bool doFullCheckpoint = !g_instance.attr.attr_storage.enableIncrementalCheckpoint;
     TransactionId oldest_active_xid = InvalidTransactionId;
+    TransactionId globalXmin = InvalidTransactionId;
 
     /*
      * An end-of-recovery checkpoint is really a shutdown checkpoint, just
@@ -10045,8 +10046,11 @@ void CreateCheckPoint(int flags)
      * pointer. This allows us to begin accumulating changes to assemble our
      * starting snapshot of locks and transactions.
      */
+    if (!shutdown) {
+        oldest_active_xid = GetOldestActiveTransactionId(&globalXmin);
+    }
     if (!shutdown && XLogStandbyInfoActive()) {
-        checkPoint.oldestActiveXid = oldest_active_xid = GetOldestActiveTransactionId();
+        checkPoint.oldestActiveXid = oldest_active_xid;
     } else {
         checkPoint.oldestActiveXid = InvalidTransactionId;
     }
@@ -10334,8 +10338,8 @@ void CreateCheckPoint(int flags)
              * local oldest active xid may lower than oldestxmin,
              * don't truncate it for safe.
              */
-            if (TransactionIdIsNormal(oldest_active_xid) && TransactionIdPrecedes(oldest_active_xid, cutoff_xid)) {
-                cutoff_xid = oldest_active_xid;
+            if (TransactionIdIsNormal(globalXmin) && TransactionIdPrecedes(globalXmin, cutoff_xid)) {
+                cutoff_xid = globalXmin;
             }
             TruncateCSNLOG(cutoff_xid);
             t_thrd.checkpoint_cxt.last_truncate_log_time = now;
diff --git a/src/gausskernel/storage/ipc/procarray.cpp b/src/gausskernel/storage/ipc/procarray.cpp
index 9264425504..a9782d7106 100644
--- a/src/gausskernel/storage/ipc/procarray.cpp
+++ b/src/gausskernel/storage/ipc/procarray.cpp
@@ -2038,12 +2038,18 @@ Datum pg_get_running_xacts(PG_FUNCTION_ARGS)
  * simple as possible and leave GetSnapshotData() as the primary code for
  * that bookkeeping.
  */
-TransactionId GetOldestActiveTransactionId()
+TransactionId GetOldestActiveTransactionId(TransactionId *globalXmin)
 {
     ProcArrayStruct* arrayP = g_instance.proc_array_idx;
     TransactionId oldestRunningXid;
     int index;
 
+    /* xmax is always latestCompletedXid + 1 */
+    TransactionId xmax = t_thrd.xact_cxt.ShmemVariableCache->latestCompletedXid;
+    Assert(TransactionIdIsNormal(xmax));
+    TransactionIdAdvance(xmax);
+    TransactionId xmin = xmax;
+
     Assert(!RecoveryInProgress());
 
     LWLockAcquire(ProcArrayLock, LW_SHARED);
@@ -2065,6 +2071,12 @@ TransactionId GetOldestActiveTransactionId()
         volatile PGXACT* pgxact = &g_instance.proc_base_all_xacts[pgprocno];
         TransactionId xid;
 
+        /* Update globalxmin to be the smallest valid xmin */
+        xid = pgxact->xmin; /* fetch just once */
+
+        if (TransactionIdIsNormal(xid) && TransactionIdPrecedes(xid, xmin))
+            xmin = xid;
+
         /* Fetch xid just once - see GetNewTransactionId */
         xid = pgxact->xid;
 
@@ -2083,6 +2095,15 @@ TransactionId GetOldestActiveTransactionId()
 
     LWLockRelease(ProcArrayLock);
 
+    /*
+     * Update globalxmin to include actual process xids.  This is a slightly
+     * different way of computing it than GetOldestXmin uses, but should give
+     * the same result.
+     */
+    if (TransactionIdPrecedes(oldestRunningXid, xmin)) {
+        xmin = oldestRunningXid;
+    }
+    *globalXmin = xmin;
     return oldestRunningXid;
 }
 
@@ -4054,12 +4075,6 @@ void CalculateLocalLatestSnapshot(bool forceCalc)
             volatile PGXACT* pgxact = &g_instance.proc_base_all_xacts[pgprocno];
             TransactionId xid;
 
-            /* Update globalxmin to be the smallest valid xmin */
-            xid = pgxact->xmin; /* fetch just once */
-
-            if (TransactionIdIsNormal(xid) && TransactionIdPrecedes(xid, globalxmin))
-                globalxmin = xid;
-
             /*
              * Backend is doing logical decoding which manages xmin
              * separately, check below.
@@ -4071,6 +4086,12 @@ void CalculateLocalLatestSnapshot(bool forceCalc)
             if (pgxact->vacuumFlags & PROC_IN_VACUUM)
                 continue;
 
+            /* Update globalxmin to be the smallest valid xmin */
+            xid = pgxact->xmin; /* fetch just once */
+
+            if (TransactionIdIsNormal(xid) && TransactionIdPrecedes(xid, globalxmin))
+                globalxmin = xid;
+
             /* Fetch xid just once - see GetNewTransactionId */
             xid = pgxact->xid;
 
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index 94602e0a7b..bcd2919327 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -62,7 +62,7 @@ extern bool TransactionIdIsActive(TransactionId xid);
 extern TransactionId GetRecentGlobalXmin(void);
 extern TransactionId GetOldestXmin(Relation rel, bool bFixRecentGlobalXmin = false);
 extern void CheckCurrentTimeline(GTM_Timeline timeline);
-extern TransactionId GetOldestActiveTransactionId(void);
+extern TransactionId GetOldestActiveTransactionId(TransactionId *globalXmin);
 extern void FixCurrentSnapshotByGxid(TransactionId gxid);
 extern void CheckSnapshotIsValidException(Snapshot snapshot, const char* location);
 extern TransactionId GetOldestSafeDecodingTransactionId(bool catalogOnly);
-- 
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