Trac Ticket #84 - 389 Directory Server Unnecessary Checkpoints

https://fedorahosted.org/389/ticket/84

Fix description: txn_checkpoint was always called with DB_FORCE flag.
This patch introduces db_force arg to dblayer_txn_checkpoint and
DB_FORCE is passed only from dblayer_force_checkpoint.

Note: checkpoint_threadmain is one of the BDB housekeeping threads.
It calls txn_checkpoint periodically. The interval is specified in
the ldbm database config:
  dn: cn=config,cn=ldbm database,cn=plugins,cn=config
  nsslapd-db-checkpoint-interval: <second>
Even if DB_FORCE is not set and there is no db modify activities,
as long as checkpoint thread is functioning, some disk IO is
observed due to updating the lock table and mempool to check if
there is any data to flush.

ldap/servers/slapd/back-ldbm/dblayer.c

@@ -343,7 +343,7 @@ dblayer_get_batch_transactions(void *arg) {
 
 static int
 dblayer_txn_checkpoint(struct ldbminfo *li, struct dblayer_private_env *env,
-                       PRBool use_lock, PRBool busy_skip)
+                       PRBool use_lock, PRBool busy_skip, PRBool db_force)
 {
     int ret = 0;
     if (busy_skip && is_anyinstance_busy(li))
@@ -351,7 +351,7 @@ dblayer_txn_checkpoint(struct ldbminfo *li, struct dblayer_private_env *env,
         return ret;
     }
     DB_CHECKPOINT_LOCK(use_lock, env->dblayer_env_lock);
-    ret = TXN_CHECKPOINT(env->dblayer_DB_ENV, 0, 0, DB_FORCE);
+    ret = TXN_CHECKPOINT(env->dblayer_DB_ENV, 0, 0, db_force?DB_FORCE:0);
     DB_CHECKPOINT_UNLOCK(use_lock, env->dblayer_env_lock);
     return ret;
 }
@@ -3675,10 +3675,7 @@ static int deadlock_threadmain(void *param)
             if (dblayer_db_uses_locking(priv->dblayer_env->dblayer_DB_ENV)) {
                 int aborted;
                 if ((rval = LOCK_DETECT(priv->dblayer_env->dblayer_DB_ENV,
-                            0,
-                            DB_LOCK_YOUNGEST,
-                            &aborted))
-                    != 0) {
+                                        0, DB_LOCK_YOUNGEST, &aborted)) != 0) {
                     LDAPDebug(LDAP_DEBUG_ANY,
                       "Serious Error---Failed in deadlock detect (aborted at 0x%x), err=%d (%s)\n",
                       aborted, rval, dblayer_strerror(rval));
@@ -3852,7 +3849,8 @@ static int checkpoint_threadmain(void *param)
         /* now checkpoint */
         checkpoint_debug_message(debug_checkpointing,
                                  "Starting checkpoint\n", 0, 0, 0);
-        rval = dblayer_txn_checkpoint(li, priv->dblayer_env, PR_TRUE, PR_TRUE);
+        rval = dblayer_txn_checkpoint(li, priv->dblayer_env, 
+                                      PR_TRUE, PR_TRUE, PR_FALSE);
 #if 1000*DB_VERSION_MAJOR + 100*DB_VERSION_MINOR < 4100
         if (DB_INCOMPLETE == rval) 
         {
@@ -3879,7 +3877,8 @@ static int checkpoint_threadmain(void *param)
 
         checkpoint_debug_message(debug_checkpointing,
                                  "Starting checkpoint\n", 0, 0, 0);
-        rval = dblayer_txn_checkpoint(li, priv->dblayer_env, PR_TRUE, PR_TRUE);
+        rval = dblayer_txn_checkpoint(li, priv->dblayer_env, 
+                                      PR_TRUE, PR_TRUE, PR_FALSE);
 #if 1000*DB_VERSION_MAJOR + 100*DB_VERSION_MINOR < 4100
         if (DB_INCOMPLETE == rval) 
         {
@@ -3990,10 +3989,9 @@ static int trickle_threadmain(void *param)
                  (0 != priv->dblayer_trickle_percentage) )
             {
                 int pages_written = 0;
-                if ((rval = MEMP_TRICKLE(
-                                      priv->dblayer_env->dblayer_DB_ENV,
-                                      priv->dblayer_trickle_percentage,
-                                      &pages_written)) != 0)
+                if ((rval = MEMP_TRICKLE(priv->dblayer_env->dblayer_DB_ENV,
+                                         priv->dblayer_trickle_percentage,
+                                         &pages_written)) != 0)
                 {
                     LDAPDebug(LDAP_DEBUG_ANY,"Serious Error---Failed to trickle, err=%d (%s)\n",rval,dblayer_strerror(rval), 0);
                 }
@@ -4385,7 +4383,7 @@ static int dblayer_force_checkpoint(struct ldbminfo *li)
      */
     
     for (i = 0; i < 2; i++) {
-      ret = dblayer_txn_checkpoint(li, pEnv, PR_TRUE, PR_FALSE);
+      ret = dblayer_txn_checkpoint(li, pEnv, PR_TRUE, PR_FALSE, PR_TRUE);
       if (ret == 0) continue;
 #if 1000*DB_VERSION_MAJOR + 100*DB_VERSION_MINOR < 4100
       if (ret != DB_INCOMPLETE)
@@ -4400,7 +4398,7 @@ static int dblayer_force_checkpoint(struct ldbminfo *li)
       LDAPDebug(LDAP_DEBUG_ANY, "Busy: retrying checkpoint\n", 0, 0, 0);
       
       /* teletubbies: "again! again!" */
-      ret = dblayer_txn_checkpoint(li, pEnv, PR_TRUE, PR_FALSE);
+      ret = dblayer_txn_checkpoint(li, pEnv, PR_TRUE, PR_FALSE, PR_TRUE);
       if (ret == DB_INCOMPLETE) {
         LDAPDebug(LDAP_DEBUG_ANY, "Busy: giving up on checkpoint\n", 0, 0, 0);
         break;