Attachment 15675 Details for Bug 14036 – Patch to potentially keep locking.tdb smaller

Patch to potentially keep locking.tdb smaller

patch.txt (text/plain), 2.12 KB, created by Volker Lendecke on 2019-12-10 19:56:56 UTC

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Creator: Volker Lendecke

Created: 2019-12-10 19:56:56 UTC

Size: 2.12 KB

patch

obsolete

>From 6820ae9279eb56def95f694f9a1ac921eeffcb08 Mon Sep 17 00:00:00 2001
>From: Volker Lendecke <vl@samba.org>
>Date: Sun, 24 Nov 2019 08:31:42 +0100
>Subject: [PATCH] tdb: Only create dead records under freelist contention
>
>When TDB_VOLATILE was invented, even looking at the freelist in a
>nonblocking fashion created an expensive fcntl lock. So we always
>create dead records, to avoid even the nonblocking freelist lock.
>
>Doing a nonblocking mutex lock is much cheaper. With this patch
>records are moved to the freelist without creating dead records. This
>shrinks the database size on lightly loaded systems significantly.
>
>Signed-off-by: Volker Lendecke <vl@samba.org>
>---
> lib/tdb/common/tdb.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
>
>diff --git a/lib/tdb/common/tdb.c b/lib/tdb/common/tdb.c
>index c56b37be5ca..6c1b1f0f2b4 100644
>--- a/lib/tdb/common/tdb.c
>+++ b/lib/tdb/common/tdb.c
>@@ -418,6 +418,17 @@ int tdb_trim_dead(struct tdb_context *tdb, uint32_t hash)
> 		return -1;
> 	}
> 
>+	/*
>+	 * Try to lock the freelist in a nonblocking way. In the loop
>+	 * below this means that if the freelist is not contended, we
>+	 * directly free all dead records.
>+	 */
>+
>+	ret = tdb_lock_nonblock(tdb, -1, F_WRLCK);
>+	if (ret == 0) {
>+		locked_freelist = true;
>+	}
>+
> 	while (rec_ptr != 0) {
> 		bool deleted = false;
> 		uint32_t next;
>@@ -438,20 +449,20 @@ int tdb_trim_dead(struct tdb_context *tdb, uint32_t hash)
> 		if (rec.magic == TDB_DEAD_MAGIC) {
> 			num_dead += 1;
> 
>-			if (num_dead > tdb->max_dead_records) {
>-
>-				if (!locked_freelist) {
>-					/*
>-					 * Lock the freelist only if
>-					 * it's really required.
>-					 */
>-					ret = tdb_lock(tdb, -1, F_WRLCK);
>-					if (ret == -1) {
>-						goto fail;
>-					};
>-					locked_freelist = true;
>-				}
>+			if ((num_dead > tdb->max_dead_records) &&
>+			    !locked_freelist) {
>+				/*
>+				 * Lock the freelist only if it's
>+				 * really required.
>+				 */
>+				ret = tdb_lock(tdb, -1, F_WRLCK);
>+				if (ret == -1) {
>+					goto fail;
>+				};
>+				locked_freelist = true;
>+			}
> 
>+			if (locked_freelist) {
> 				ret = tdb_del_dead(
> 					tdb,
> 					last_ptr,
>-- 
>2.20.1
>

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