From: Volker Lendecke <vl@samba.org>
Date: Mon, 22 Oct 2018 08:10:24 +0000 (+0200)
Subject: tdb: Remove "USE_RIGHT_MERGES" code
X-Git-Tag: tdb-1.3.17~1214
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8df11518c0df90aa0c223b2e964fc86015f77e2c;p=thirdparty%2Fsamba.git

tdb: Remove "USE_RIGHT_MERGES" code

This has not been activated by default for ages and can be very
inefficient. With check_merge_with_left_record() we have an
alternative that will merge freelist records while we walk it
anyway. This has reduced fragmentation significantly

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
---

diff --git a/lib/tdb/common/freelist.c b/lib/tdb/common/freelist.c
index e4bbfce0027..5afd89bc554 100644
--- a/lib/tdb/common/freelist.c
+++ b/lib/tdb/common/freelist.c
@@ -27,12 +27,6 @@
 
 #include "tdb_private.h"
 
-/* 'right' merges can involve O(n^2) cost when combined with a
-   traverse, so they are disabled until we find a way to do them in
-   O(1) time
-*/
-#define USE_RIGHT_MERGES 0
-
 /* read a freelist record and check for simple errors */
 int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off, struct tdb_record *rec)
 {
@@ -61,30 +55,6 @@ int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off, struct tdb_record
 	return 0;
 }
 
-
-#if USE_RIGHT_MERGES
-/* Remove an element from the freelist.  Must have alloc lock. */
-static int remove_from_freelist(struct tdb_context *tdb, tdb_off_t off, tdb_off_t next)
-{
-	tdb_off_t last_ptr, i;
-
-	/* read in the freelist top */
-	last_ptr = FREELIST_TOP;
-	while (tdb_ofs_read(tdb, last_ptr, &i) != -1 && i != 0) {
-		if (i == off) {
-			/* We've found it! */
-			return tdb_ofs_write(tdb, last_ptr, &next);
-		}
-		/* Follow chain (next offset is at start of record) */
-		last_ptr = i;
-	}
-	tdb->ecode = TDB_ERR_CORRUPT;
-	TDB_LOG((tdb, TDB_DEBUG_FATAL,"remove_from_freelist: not on list at off=%u\n", off));
-	return -1;
-}
-#endif
-
-
 /* update a record tailer (must hold allocation lock) */
 static int update_tailer(struct tdb_context *tdb, tdb_off_t offset,
 			 const struct tdb_record *rec)
@@ -318,33 +288,6 @@ int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct tdb_record *rec)
 		goto fail;
 	}
 
-#if USE_RIGHT_MERGES
-	/* Look right first (I'm an Australian, dammit) */
-	if (offset + sizeof(*rec) + rec->rec_len + sizeof(*rec) <= tdb->map_size) {
-		tdb_off_t right = offset + sizeof(*rec) + rec->rec_len;
-		struct tdb_record r;
-
-		if (tdb->methods->tdb_read(tdb, right, &r, sizeof(r), DOCONV()) == -1) {
-			TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right read failed at %u\n", right));
-			goto left;
-		}
-
-		/* If it's free, expand to include it. */
-		if (r.magic == TDB_FREE_MAGIC) {
-			if (remove_from_freelist(tdb, right, r.next) == -1) {
-				TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right free failed at %u\n", right));
-				goto left;
-			}
-			rec->rec_len += sizeof(r) + r.rec_len;
-			if (update_tailer(tdb, offset, rec) == -1) {
-				TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed at %u\n", offset));
-				goto fail;
-			}
-		}
-	}
-left:
-#endif
-
 	ret = check_merge_with_left_record(tdb, offset, rec, NULL, NULL);
 	if (ret == -1) {
 		goto fail;