Date: Fri, 6 Dec 2019 10:23:25 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: pgsql-hackers@postgresql.org
Cc: Andres Freund <andres@anarazel.de>
Subject: Re: error context for vacuum to include block number
Message-ID: <20191206162325.GQ2082@telsasoft.com>
References: <20191120210600.GC30362@telsasoft.com>
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Find attached updated patch:
 . Use structure to include relation name.
 . Split into a separate patch rename of "StringInfoData buf".

2019-11-27 20:04:53.640 CST [14244] ERROR:  canceling statement due to statement timeout
2019-11-27 20:04:53.640 CST [14244] CONTEXT:  block 2314 of relation t
2019-11-27 20:04:53.640 CST [14244] STATEMENT:  vacuum t;

I tried to use BufferGetTag() to avoid using a 2ndary structure, but fails if
the buffer is not pinned.

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 filename="v2-0001-vacuum-errcontext-to-show-block-being-processed.patch"

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


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 filename="v2-0002-Rename-buf-to-avoid-shadowing-buf-of-another-type.patch"

From db5cf19bc6d29eb8b9cb5cf251abc8d2a18e97dc Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Wed, 27 Nov 2019 20:07:10 -0600
Subject: [PATCH v2 2/2] Rename buf to avoid shadowing buf of another type

---
 src/backend/access/heap/vacuumlazy.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 774cad5..e17c4cc 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -523,7 +523,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 	BlockNumber next_unskippable_block;
 	bool		skipping_blocks;
 	xl_heap_freeze_tuple *frozen;
-	StringInfoData buf;
+	StringInfoData sbuf;
 	const int	initprog_index[] = {
 		PROGRESS_VACUUM_PHASE,
 		PROGRESS_VACUUM_TOTAL_HEAP_BLKS,
@@ -1502,33 +1502,33 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 	 * This is pretty messy, but we split it up so that we can skip emitting
 	 * individual parts of the message when not applicable.
 	 */
-	initStringInfo(&buf);
-	appendStringInfo(&buf,
+	initStringInfo(&sbuf);
+	appendStringInfo(&sbuf,
 					 _("%.0f dead row versions cannot be removed yet, oldest xmin: %u\n"),
 					 nkeep, OldestXmin);
-	appendStringInfo(&buf, _("There were %.0f unused item identifiers.\n"),
+	appendStringInfo(&sbuf, _("There were %.0f unused item identifiers.\n"),
 					 nunused);
-	appendStringInfo(&buf, ngettext("Skipped %u page due to buffer pins, ",
+	appendStringInfo(&sbuf, ngettext("Skipped %u page due to buffer pins, ",
 									"Skipped %u pages due to buffer pins, ",
 									vacrelstats->pinskipped_pages),
 					 vacrelstats->pinskipped_pages);
-	appendStringInfo(&buf, ngettext("%u frozen page.\n",
+	appendStringInfo(&sbuf, ngettext("%u frozen page.\n",
 									"%u frozen pages.\n",
 									vacrelstats->frozenskipped_pages),
 					 vacrelstats->frozenskipped_pages);
-	appendStringInfo(&buf, ngettext("%u page is entirely empty.\n",
+	appendStringInfo(&sbuf, ngettext("%u page is entirely empty.\n",
 									"%u pages are entirely empty.\n",
 									empty_pages),
 					 empty_pages);
-	appendStringInfo(&buf, _("%s."), pg_rusage_show(&ru0));
+	appendStringInfo(&sbuf, _("%s."), pg_rusage_show(&ru0));
 
 	ereport(elevel,
 			(errmsg("\"%s\": found %.0f removable, %.0f nonremovable row versions in %u out of %u pages",
 					RelationGetRelationName(onerel),
 					tups_vacuumed, num_tuples,
 					vacrelstats->scanned_pages, nblocks),
-			 errdetail_internal("%s", buf.data)));
-	pfree(buf.data);
+			 errdetail_internal("%s", sbuf.data)));
+	pfree(sbuf.data);
 }
 
 
-- 
2.7.4


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