From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Thu, 12 Dec 2019 20:54:37 -0600
Subject: [PATCH v5 4/5] vacuum errcontext to show block being processed

As requested here.
https://www.postgresql.org/message-id/20190807235154.erbmr4o4bo6vgnjv%40alap3.anarazel.de
---
 src/backend/access/heap/vacuumlazy.c | 38 ++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 145a8a2..5f44543 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -138,6 +138,12 @@ typedef struct LVRelStats
 	bool		lock_waiter_detected;
 } LVRelStats;
 
+typedef struct
+{
+	char *relname;
+	char *relnamespace;
+	BlockNumber blkno;
+} vacuum_error_callback_arg;
 
 /* A few variables that don't seem worth passing around as parameters */
 static int	elevel = -1;
@@ -176,6 +182,7 @@ static bool lazy_tid_reaped(ItemPointer itemptr, void *state);
 static int	vac_cmp_itemptr(const void *left, const void *right);
 static bool heap_page_is_all_visible(Relation rel, Buffer buf,
 									 TransactionId *visibility_cutoff_xid, bool *all_frozen);
+static void vacuum_error_callback(void *arg);
 
 
 /*
@@ -525,6 +532,8 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 		PROGRESS_VACUUM_MAX_DEAD_TUPLES
 	};
 	int64		initprog_val[3];
+	ErrorContextCallback errcallback;
+	vacuum_error_callback_arg errcbarg;
 
 	pg_rusage_init(&ru0);
 
@@ -636,6 +645,15 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 	else
 		skipping_blocks = false;
 
+	/* Setup error traceback support for ereport() */
+	errcallback.callback = vacuum_error_callback;
+	errcbarg.relname = relname;
+	errcbarg.relnamespace = get_namespace_name(RelationGetNamespace(onerel));
+	errcbarg.blkno = InvalidBlockNumber; /* Not known yet */
+	errcallback.arg = (void *) &errcbarg;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
 	for (blkno = 0; blkno < nblocks; blkno++)
 	{
 		Buffer		buf;
@@ -657,6 +675,8 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 #define FORCE_CHECK_PAGE() \
 		(blkno == nblocks - 1 && should_attempt_truncation(params, vacrelstats))
 
+		errcbarg.blkno = blkno;
+
 		pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
 
 		if (blkno == next_unskippable_block)
@@ -754,7 +774,10 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 			}
 
 
+			/* Don't use the errcontext handler outside this function */
+			error_context_stack = errcallback.previous;
 			lazy_vacuum_heap_index(onerel, vacrelstats, Irel, nindexes, indstats);
+			error_context_stack = &errcallback;
 
 			/*
 			 * Forget the now-vacuumed tuples, and press on, but be careful
@@ -1359,6 +1382,9 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 			RecordPageWithFreeSpace(onerel, blkno, freespace);
 	}
 
+	/* Pop the error context stack */
+	error_context_stack = errcallback.previous;
+
 	/* report that everything is scanned and vacuumed */
 	pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
 
@@ -2335,3 +2361,15 @@ heap_page_is_all_visible(Relation rel, Buffer buf,
 
 	return all_visible;
 }
+
+/*
+ * Error context callback for errors occurring during vacuum.
+ */
+static void
+vacuum_error_callback(void *arg)
+{
+	vacuum_error_callback_arg *cbarg = arg;
+
+	errcontext("while scanning block %u of relation \"%s.%s\"",
+			cbarg->blkno, cbarg->relnamespace, cbarg->relname);
+}
-- 
2.7.4


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