From 41e1d6d118346e84aac7cfe68424f7452c7dcb8d Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Wed, 20 Nov 2019 14:53:20 -0600
Subject: [PATCH v2 1/2] 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 | 40 ++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index a3c4a1d..774cad5 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -138,6 +138,11 @@ typedef struct LVRelStats
 	bool		lock_waiter_detected;
 } LVRelStats;
 
+typedef struct
+{
+	char *relname;
+	BlockNumber blkno;
+} vacuum_error_callback_arg;
 
 /* A few variables that don't seem worth passing around as parameters */
 static int	elevel = -1;
@@ -175,6 +180,7 @@ 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);
 
 
 /*
@@ -524,6 +530,8 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 		PROGRESS_VACUUM_MAX_DEAD_TUPLES
 	};
 	int64		initprog_val[3];
+	ErrorContextCallback errcallback;
+	vacuum_error_callback_arg cbarg;
 
 	pg_rusage_init(&ru0);
 
@@ -635,6 +643,14 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 	else
 		skipping_blocks = false;
 
+	/* Setup error traceback support for ereport() */
+	errcallback.callback = vacuum_error_callback;
+	cbarg.relname = relname;
+	cbarg.blkno = 0; /* Not known yet */
+	errcallback.arg = (void *) &cbarg;
+	errcallback.previous = error_context_stack;
+	error_context_stack = &errcallback;
+
 	for (blkno = 0; blkno < nblocks; blkno++)
 	{
 		Buffer		buf;
@@ -657,6 +673,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 		(blkno == nblocks - 1 && should_attempt_truncation(params, vacrelstats))
 
 		pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
+		cbarg.blkno = blkno;
 
 		if (blkno == next_unskippable_block)
 		{
@@ -817,6 +834,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 
 		buf = ReadBufferExtended(onerel, MAIN_FORKNUM, blkno,
 								 RBM_NORMAL, vac_strategy);
+		// errcallback.arg = (void *) &buf;
 
 		/* We need buffer cleanup lock so that we can prune HOT chains. */
 		if (!ConditionalLockBufferForCleanup(buf))
@@ -1388,6 +1406,9 @@ 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);
 
@@ -2354,3 +2375,22 @@ 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("block %u of relation %s", cbarg->blkno, cbarg->relname);
+	// Buffer *buf = arg;
+	// RelFileNode rnode;
+	// ForkNumber forknum;
+	// BlockNumber blknum;
+	// char *path;
+	// BufferGetTag(*buf, &rnode, &forknum, &blknum);
+	// path = relpathperm(rnode, forknum);
+	// errcontext("block %u of relation %s", blknum, path);
+	// pfree(path);
+}
-- 
2.7.4