[PATCH] make gencache hash size configurable

[Volker Lendecke]

Hi!

Review appreciated!

Thanks, Volker
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>From 627bafeb1e7165fbc51f5d2de3232bb528dbd0a5 Mon Sep 17 00:00:00 2001
From: Volker Lendecke <vl at samba.org>
Date: Mon, 6 Feb 2017 17:10:40 +0100
Subject: [PATCH] lib: Make gencache hash size configurable, default to 10000

For large deployments with many users, we put a lot of idmapping
entries into gencache. Increase the hash size from our default 131.

Signed-off-by: Volker Lendecke <vl at samba.org>
---
 source3/lib/gencache.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/source3/lib/gencache.c b/source3/lib/gencache.c
index 2c1704e..1572825 100644
--- a/source3/lib/gencache.c
+++ b/source3/lib/gencache.c
@@ -55,12 +55,15 @@ static bool gencache_init(void)
 {
 	char* cache_fname = NULL;
 	int open_flags = O_RDWR|O_CREAT;
+	int hash_size;
 
 	/* skip file open if it's already opened */
 	if (cache) {
 		return true;
 	}
 
+	hash_size = lp_parm_int(-1, "gencache", "hash_size", 10000);
+
 	cache_fname = cache_path("gencache.tdb");
 	if (cache_fname == NULL) {
 		return false;
@@ -68,7 +71,7 @@ static bool gencache_init(void)
 
 	DEBUG(5, ("Opening cache file at %s\n", cache_fname));
 
-	cache = tdb_wrap_open(NULL, cache_fname, 0,
+	cache = tdb_wrap_open(NULL, cache_fname, hash_size,
 			      TDB_DEFAULT|TDB_INCOMPATIBLE_HASH,
 			      open_flags, 0644);
 	if (cache) {
@@ -87,7 +90,7 @@ static bool gencache_init(void)
 			 * CLEAR_IF_FIRST databases, so lets use it here to
 			 * clean up a broken database.
 			 */
-			cache = tdb_wrap_open(NULL, cache_fname, 0,
+			cache = tdb_wrap_open(NULL, cache_fname, hash_size,
 					      TDB_DEFAULT|
 					      TDB_INCOMPATIBLE_HASH|
 					      TDB_CLEAR_IF_FIRST,
@@ -97,7 +100,7 @@ static bool gencache_init(void)
 
 	if (!cache && (errno == EACCES)) {
 		open_flags = O_RDONLY;
-		cache = tdb_wrap_open(NULL, cache_fname, 0,
+		cache = tdb_wrap_open(NULL, cache_fname, hash_size,
 				      TDB_DEFAULT|TDB_INCOMPATIBLE_HASH,
 				      open_flags, 0644);
 		if (cache) {
@@ -119,7 +122,7 @@ static bool gencache_init(void)
 
 	DEBUG(5, ("Opening cache file at %s\n", cache_fname));
 
-	cache_notrans = tdb_wrap_open(NULL, cache_fname, 0,
+	cache_notrans = tdb_wrap_open(NULL, cache_fname, hash_size,
 				      TDB_CLEAR_IF_FIRST|
 				      TDB_INCOMPATIBLE_HASH|
 				      TDB_NOSYNC|
-- 
2.1.4