handle two special cases

1) when all nodes write the same value to the record, or when writing
   a value that is already there, we can skip the write and save
   ourselves a network transactions

2) when all remote nodes fail an update, and we then fail a replay, we
   don't need to trigger a recovery. This solves a corner case where
   we could get into a recovery loop

diff --git a/source/lib/dbwrap_ctdb.c b/source/lib/dbwrap_ctdb.c
index 645b93846babb426e8639b638aaa4d20b86d3994..bd062b368adb9e453a957b6e8d6995f2096db4a6 100644 (file)
--- a/source/lib/dbwrap_ctdb.c
+++ b/source/lib/dbwrap_ctdb.c
@@ -460,6 +460,14 @@ static int db_ctdb_transaction_store(struct db_ctdb_transaction_handle *h,
                header.dmaster = get_my_vnn();
        } else {
                memcpy(&header, rec.dptr, sizeof(struct ctdb_ltdb_header));
+               rec.dsize -= sizeof(struct ctdb_ltdb_header);
+               /* a special case, we are writing the same data that is there now */
+               if (data.dsize == rec.dsize &&
+                   memcmp(data.dptr, rec.dptr + sizeof(struct ctdb_ltdb_header), data.dsize) == 0) {
+                       SAFE_FREE(rec.dptr);
+                       talloc_free(tmp_ctx);
+                       return 0;
+               }
                SAFE_FREE(rec.dptr);
        }
 
@@ -472,13 +480,13 @@ static int db_ctdb_transaction_store(struct db_ctdb_transaction_handle *h,
                        talloc_free(tmp_ctx);
                        return -1;
                }
+       }
                
-               h->m_write = db_ctdb_marshall_add(h, h->m_write, h->ctx->db_id, 0, key, &header, data);
-               if (h->m_write == NULL) {
-                       DEBUG(0,(__location__ " Failed to add to marshalling record\n"));
-                       talloc_free(tmp_ctx);
-                       return -1;
-               }
+       h->m_write = db_ctdb_marshall_add(h, h->m_write, h->ctx->db_id, 0, key, &header, data);
+       if (h->m_write == NULL) {
+               DEBUG(0,(__location__ " Failed to add to marshalling record\n"));
+               talloc_free(tmp_ctx);
+               return -1;
        }
        
        rec.dsize = data.dsize + sizeof(struct ctdb_ltdb_header);
@@ -541,6 +549,8 @@ static int ctdb_replay_transaction(struct db_ctdb_transaction_handle *h)
        struct ctdb_rec_data *rec = NULL;
 
        h->in_replay = true;
+       talloc_free(h->m_write);
+       h->m_write = NULL;
 
        ret = db_ctdb_transaction_fetch_start(h);
        if (ret != 0) {
@@ -599,6 +609,7 @@ static int db_ctdb_transaction_commit(struct db_context *db)
        int status;
        int retries = 0;
        struct db_ctdb_transaction_handle *h = ctx->transaction;
+       enum ctdb_controls failure_control = CTDB_CONTROL_TRANS2_ERROR;
 
        if (h == NULL) {
                DEBUG(0,(__location__ " transaction commit with no open transaction on db 0x%08x\n", ctx->db_id));
@@ -607,13 +618,6 @@ static int db_ctdb_transaction_commit(struct db_context *db)
 
        DEBUG(5,(__location__ " Commit transaction on db 0x%08x\n", ctx->db_id));
 
-       if (h->m_write == NULL) {
-               /* no changes were made */
-               talloc_free(h);
-               ctx->transaction = NULL;
-               return 0;
-       }
-
        talloc_set_destructor(h, NULL);
 
        /* our commit strategy is quite complex.
@@ -632,6 +636,14 @@ static int db_ctdb_transaction_commit(struct db_context *db)
        */
 
 again:
+       if (h->m_write == NULL) {
+               /* no changes were made, potentially after a retry */
+               tdb_transaction_cancel(h->ctx->wtdb->tdb);
+               talloc_free(h);
+               ctx->transaction = NULL;
+               return 0;
+       }
+
        /* tell ctdbd to commit to the other nodes */
        rets = ctdbd_control_local(messaging_ctdbd_connection(), 
                                  CTDB_CONTROL_TRANS2_COMMIT, h->ctx->db_id, 0,
@@ -639,9 +651,23 @@ again:
        if (!NT_STATUS_IS_OK(rets) || status != 0) {
                tdb_transaction_cancel(h->ctx->wtdb->tdb);
                sleep(1);
+
+               /* work out what error code we will give if we 
+                  have to fail the operation */
+               switch ((enum ctdb_trans2_commit_error)status) {
+               case CTDB_TRANS2_COMMIT_SUCCESS:
+               case CTDB_TRANS2_COMMIT_SOMEFAIL:
+               case CTDB_TRANS2_COMMIT_TIMEOUT:
+                       failure_control = CTDB_CONTROL_TRANS2_ERROR;
+                       break;
+               case CTDB_TRANS2_COMMIT_ALLFAIL:
+                       failure_control = CTDB_CONTROL_TRANS2_FINISHED;
+                       break;
+               }
+
                if (ctdb_replay_transaction(h) != 0) {
                        DEBUG(0,(__location__ " Failed to replay transaction\n"));
-                       ctdbd_control_local(messaging_ctdbd_connection(), CTDB_CONTROL_TRANS2_ERROR,
+                       ctdbd_control_local(messaging_ctdbd_connection(), failure_control,
                                            h->ctx->db_id, CTDB_CTRL_FLAG_NOREPLY, 
                                            tdb_null, NULL, NULL, NULL);
                        h->ctx->transaction = NULL;
@@ -649,10 +675,10 @@ again:
                        ctx->transaction = NULL;
                        return -1;
                }
-               if (retries++ == 10) {
+               if (++retries == 10) {
                        DEBUG(0,(__location__ " Giving up transaction on db 0x%08x after %d retries\n", 
                                 h->ctx->db_id, retries));
-                       ctdbd_control_local(messaging_ctdbd_connection(), CTDB_CONTROL_TRANS2_ERROR,
+                       ctdbd_control_local(messaging_ctdbd_connection(), failure_control,
                                            h->ctx->db_id, CTDB_CTRL_FLAG_NOREPLY, 
                                            tdb_null, NULL, NULL, NULL);
                        h->ctx->transaction = NULL;