]> git.ozlabs.org Git - ccan/blobdiff - ccan/tdb/tools/replay_trace.c
Automate rerunning when we have to back off: gives accurate(ish) timings.
[ccan] / ccan / tdb / tools / replay_trace.c
index bd4b8aa804eeaca2c11626cd659d4c7345ec73f4..67809d82093e57765cd0ac5e12dfc4644b869799 100644 (file)
@@ -15,6 +15,7 @@
 #include <errno.h>
 #include <signal.h>
 #include <assert.h>
+#include <fcntl.h>
 
 #define STRINGIFY2(x) #x
 #define STRINGIFY(x) STRINGIFY2(x)
@@ -31,6 +32,7 @@ struct pipe {
        int fd[2];
 };
 static struct pipe *pipes;
+static int backoff_fd = -1;
 
 static void __attribute__((noreturn)) fail(const char *filename,
                                           unsigned int line,
@@ -119,6 +121,7 @@ enum op_type {
        OP_TDB_TRAVERSE_START,
        OP_TDB_TRAVERSE_END,
        OP_TDB_TRAVERSE,
+       OP_TDB_TRAVERSE_END_EARLY,
        OP_TDB_FIRSTKEY,
        OP_TDB_NEXTKEY,
        OP_TDB_FETCH,
@@ -126,8 +129,8 @@ enum op_type {
 };
 
 struct op {
-       unsigned int serial;
-       enum op_type op;
+       unsigned int seqnum;
+       enum op_type type;
        TDB_DATA key;
        TDB_DATA data;
        int ret;
@@ -147,10 +150,16 @@ struct op {
                        TDB_DATA pre;
                        TDB_DATA post;
                } append;
-               unsigned int group_len; /* transaction/traverse start */
+               /* transaction/traverse start/chainlock */
+               unsigned int group_len;
        };
 };
 
+struct op_desc {
+       unsigned int file;
+       unsigned int op_num;
+};
+
 static unsigned char hex_char(const char *filename, unsigned int line, char c)
 {
        c = toupper(c);
@@ -187,13 +196,13 @@ static TDB_DATA make_tdb_data(const void *ctx,
 }
 
 static void add_op(const char *filename, struct op **op, unsigned int i,
-                  unsigned int serial, enum op_type type)
+                  unsigned int seqnum, enum op_type type)
 {
        struct op *new;
        *op = talloc_realloc(NULL, *op, struct op, i+1);
        new = (*op) + i;
-       new->op = type;
-       new->serial = serial;
+       new->type = type;
+       new->seqnum = seqnum;
        new->ret = 0;
        new->group_start = 0;
 }
@@ -213,8 +222,7 @@ static void op_add_key(const char *filename,
                fail(filename, op_num+1, "Expected just a key");
 
        op[op_num].key = make_tdb_data(op, filename, op_num+1, words[2]);
-       if (op[op_num].op != OP_TDB_TRAVERSE)
-               total_keys++;
+       total_keys++;
 }
 
 static void op_add_key_ret(const char *filename,
@@ -243,7 +251,27 @@ static void op_add_key_data(const char *filename,
                total_keys++;
 }
 
-/* <serial> tdb_store <rec> <rec> <flag> = <ret> */
+/* We don't record the keys or data for a traverse, as we don't use them. */
+static void op_add_traverse(const char *filename,
+                           struct op op[], unsigned int op_num, char *words[])
+{
+       if (!words[2] || !words[3] || !words[4] || words[5]
+           || !streq(words[3], "="))
+               fail(filename, op_num+1, "Expected <key> = <data>");
+       op[op_num].key = tdb_null;
+}
+
+/* Full traverse info is useful for debugging, but changing it to
+ * "traversefn" without the data makes the traces *much* smaller! */
+static void op_add_traversefn(const char *filename,
+                           struct op op[], unsigned int op_num, char *words[])
+{
+       if (words[2])
+               fail(filename, op_num+1, "Expected no values");
+       op[op_num].key = tdb_null;
+}
+
+/* <seqnum> tdb_store <rec> <rec> <flag> = <ret> */
 static void op_add_store(const char *filename,
                         struct op op[], unsigned int op_num, char *words[])
 {
@@ -258,7 +286,7 @@ static void op_add_store(const char *filename,
        total_keys++;
 }
 
-/* <serial> tdb_append <rec> <rec> = <rec> */
+/* <seqnum> tdb_append <rec> <rec> = <rec> */
 static void op_add_append(const char *filename,
                          struct op op[], unsigned int op_num, char *words[])
 {
@@ -279,7 +307,7 @@ static void op_add_append(const char *filename,
        total_keys++;
 }
 
-/* <serial> tdb_get_seqnum = <ret> */
+/* <seqnum> tdb_get_seqnum = <ret> */
 static void op_add_seqnum(const char *filename,
                          struct op op[], unsigned int op_num, char *words[])
 {
@@ -290,8 +318,9 @@ static void op_add_seqnum(const char *filename,
        op[op_num].ret = atoi(words[3]);
 }
 
-static void op_add_traverse(const char *filename,
-                           struct op op[], unsigned int op_num, char *words[])
+static void op_add_traverse_start(const char *filename,
+                                 struct op op[],
+                                 unsigned int op_num, char *words[])
 {
        if (words[2])
                fail(filename, op_num+1, "Expect no arguments");
@@ -310,12 +339,39 @@ static void op_add_transaction(const char *filename, struct op op[],
        op[op_num].group_len = 0;
 }
 
-static int op_transaction_start(struct op op[], unsigned int op_num)
+static void op_add_chainlock(const char *filename,
+                            struct op op[], unsigned int op_num, char *words[])
+{
+       if (words[2] == NULL || words[3])
+               fail(filename, op_num+1, "Expected just a key");
+
+       /* A chainlock key isn't a key in the normal sense; it doesn't
+        * have to be in the db at all.  Also, we don't want to hash this op. */
+       op[op_num].data = make_tdb_data(op, filename, op_num+1, words[2]);
+       op[op_num].key = tdb_null;
+       op[op_num].group_len = 0;
+}
+
+static void op_add_chainlock_ret(const char *filename,
+                                struct op op[], unsigned int op_num,
+                                char *words[])
+{
+       if (!words[2] || !words[3] || !words[4] || words[5]
+           || !streq(words[3], "="))
+               fail(filename, op_num+1, "Expected <key> = <ret>");
+       op[op_num].ret = atoi(words[4]);
+       op[op_num].data = make_tdb_data(op, filename, op_num+1, words[2]);
+       op[op_num].key = tdb_null;
+       op[op_num].group_len = 0;
+       total_keys++;
+}
+
+static int op_find_start(struct op op[], unsigned int op_num, enum op_type type)
 {
        unsigned int i;
 
        for (i = op_num-1; i > 0; i--) {
-               if (op[i].op == OP_TDB_TRANSACTION_START && !op[i].group_len)
+               if (op[i].type == type && !op[i].group_len)
                        return i;
        }
        return 0;
@@ -332,7 +388,7 @@ static void op_analyze_transaction(const char *filename,
        if (words[2])
                fail(filename, op_num+1, "Expect no arguments");
 
-       start = op_transaction_start(op, op_num);
+       start = op_find_start(op, op_num, OP_TDB_TRANSACTION_START);
        if (!start)
                fail(filename, op_num+1, "no transaction start found");
 
@@ -343,10 +399,35 @@ static void op_analyze_transaction(const char *filename,
                op[i].group_start = start;
 }
 
-struct traverse_hash {
-       TDB_DATA key;
-       unsigned int index;
-};
+/* We treat chainlocks a lot like transactions, even though that's overkill */
+static void op_analyze_chainlock(const char *filename,
+                                struct op op[], unsigned int op_num,
+                                char *words[])
+{
+       unsigned int i, start;
+
+       if (words[2] == NULL || words[3])
+               fail(filename, op_num+1, "Expected just a key");
+
+       op[op_num].data = make_tdb_data(op, filename, op_num+1, words[2]);
+       op[op_num].key = tdb_null;
+       total_keys++;
+
+       start = op_find_start(op, op_num, OP_TDB_CHAINLOCK);
+       if (!start)
+               start = op_find_start(op, op_num, OP_TDB_CHAINLOCK_READ);
+       if (!start)
+               fail(filename, op_num+1, "no initial chainlock found");
+
+       /* FIXME: We'd have to do something clever to make this work
+        * vs. deadlock. */
+       if (!key_eq(op[start].data, op[op_num].data))
+               fail(filename, op_num+1, "nested chainlock calls?");
+
+       op[start].group_len = op_num - start;
+       for (i = start; i <= op_num; i++)
+               op[i].group_start = start;
+}
 
 static void op_analyze_traverse(const char *filename,
                                struct op op[], unsigned int op_num,
@@ -364,23 +445,18 @@ static void op_analyze_traverse(const char *filename,
        } else
                op[op_num].ret = 0;
 
-       for (i = op_num-1; i >= 0; i--) {
-               if (op[i].op != OP_TDB_TRAVERSE_READ_START
-                   && op[i].op != OP_TDB_TRAVERSE_START)
-                       continue;
-               if (op[i].group_len)
-                       continue;
-               break;
-       }
-
-       if (i < 0)
+       start = op_find_start(op, op_num, OP_TDB_TRAVERSE_START);
+       if (!start)
+               start = op_find_start(op, op_num, OP_TDB_TRAVERSE_READ_START);
+       if (!start)
                fail(filename, op_num+1, "no traversal start found");
 
-       start = i;
        op[start].group_len = op_num - start;
 
+       /* Don't roll in nested traverse/chainlock */
        for (i = start; i <= op_num; i++)
-               op[i].group_start = start;
+               if (!op[i].group_start)
+                       op[i].group_start = start;
 }
 
 /* Keep -Wmissing-declarations happy: */
@@ -393,10 +469,8 @@ struct depend {
        /* We can have more than one */
        struct list_node pre_list;
        struct list_node post_list;
-       unsigned int needs_file;
-       unsigned int needs_opnum;
-       unsigned int satisfies_file;
-       unsigned int satisfies_opnum;
+       struct op_desc needs;
+       struct op_desc prereq;
 };
 
 static void check_deps(const char *filename, struct op op[], unsigned int num)
@@ -416,11 +490,11 @@ static void dump_pre(char *filename[], struct op *op[],
        struct depend *dep;
 
        printf("%s:%u (%u) still waiting for:\n", filename[file], i+1,
-               op[file][i].serial);
+               op[file][i].seqnum);
        list_for_each(&op[file][i].pre, dep, pre_list)
                printf("    %s:%u (%u)\n",
-                      filename[dep->satisfies_file], dep->satisfies_opnum+1,
-                      op[dep->satisfies_file][dep->satisfies_opnum].serial);
+                      filename[dep->prereq.file], dep->prereq.op_num+1,
+                      op[dep->prereq.file][dep->prereq.op_num].seqnum);
        check_deps(filename[file], op[file], i);
 }
 
@@ -444,8 +518,12 @@ static bool do_pre(struct tdb_context *tdb,
                while (read(pre_fd, &dep, sizeof(dep)) != sizeof(dep)) {
                        if (errno == EINTR) {
                                if (backoff) {
+                                       struct op_desc desc = { file,i };
                                        warnx("%s:%u:avoiding deadlock",
                                              filename[file], i+1);
+                                       if (write(backoff_fd, &desc,
+                                                 sizeof(desc)) != sizeof(desc))
+                                               err(1, "writing backoff_fd");
                                        return false;
                                }
                                dump_pre(filename, op, file, i);
@@ -457,8 +535,8 @@ static bool do_pre(struct tdb_context *tdb,
 
 #if DEBUG_DEPS
                printf("%s:%u:got pre %u from %s:%u\n", filename[file], i+1,
-                      dep->needs_opnum+1, filename[dep->satisfies_file],
-                      dep->satisfies_opnum+1);
+                      dep->needs.op_num+1, filename[dep->prereq.file],
+                      dep->prereq.op_num+1);
                fflush(stdout);
 #endif
                /* This could be any op, not just this one. */
@@ -475,12 +553,12 @@ static void do_post(char *filename[], struct op *op[],
        list_for_each(&op[file][i].post, dep, post_list) {
 #if DEBUG_DEPS
                printf("%s:%u:sending to file %s:%u\n", filename[file], i+1,
-                      filename[dep->needs_file], dep->needs_opnum+1);
+                      filename[dep->needs.file], dep->needs.op_num+1);
 #endif
-               if (write(pipes[dep->needs_file].fd[1], &dep, sizeof(dep))
+               if (write(pipes[dep->needs.file].fd[1], &dep, sizeof(dep))
                    != sizeof(dep))
                        err(1, "%s:%u failed to tell file %s",
-                           filename[file], i+1, filename[dep->needs_file]);
+                           filename[file], i+1, filename[dep->needs.file]);
        }
 }
 
@@ -523,7 +601,7 @@ static int nontrivial_traverse(struct tdb_context *tdb,
                     "traverse did not terminate");
        }
 
-       if (tinfo->op[tinfo->file][tinfo->i].op != OP_TDB_TRAVERSE)
+       if (tinfo->op[tinfo->file][tinfo->i].type != OP_TDB_TRAVERSE)
                fail(tinfo->filename[tinfo->file], tinfo->start + 1,
                     "%s:%u:traverse terminated early");
 
@@ -536,8 +614,8 @@ static int nontrivial_traverse(struct tdb_context *tdb,
                           tinfo->file, tinfo->i+1, tinfo->start + trav_len,
                           avoid_deadlock);
 
-       /* We backed off, or we hit OP_TDB_TRAVERSE_END. */
-       if (tinfo->op[tinfo->file][tinfo->i].op != OP_TDB_TRAVERSE)
+       /* We backed off, or we hit OP_TDB_TRAVERSE_END/EARLY. */
+       if (tinfo->op[tinfo->file][tinfo->i].type != OP_TDB_TRAVERSE)
                return 1;
 
        return 0;
@@ -561,7 +639,8 @@ static unsigned op_traverse(struct tdb_context *tdb,
         * original traverse went A (delete A), B, we might do B
         * (delete A).  So if we have ops left over, we do it now. */
        while (tinfo.i != start + op[file][start].group_len) {
-               if (op[file][tinfo.i].op == OP_TDB_TRAVERSE)
+               if (op[file][tinfo.i].type == OP_TDB_TRAVERSE
+                   || op[file][tinfo.i].type == OP_TDB_TRAVERSE_END_EARLY)
                        tinfo.i++;
                else
                        tinfo.i = run_ops(tdb, pre_fd, filename, op, file,
@@ -597,7 +676,7 @@ unsigned run_ops(struct tdb_context *tdb,
                if (!do_pre(tdb, filename, op, file, pre_fd, i, backoff))
                        return i;
 
-               switch (op[file][i].op) {
+               switch (op[file][i].type) {
                case OP_TDB_LOCKALL:
                        try(tdb_lockall(tdb), op[file][i].ret);
                        break;
@@ -697,6 +776,7 @@ unsigned run_ops(struct tdb_context *tdb,
                                        tdb_traverse, op, i);
                        break;
                case OP_TDB_TRAVERSE:
+               case OP_TDB_TRAVERSE_END_EARLY:
                        /* Terminate: we're in a traverse, and we've
                         * done our ops. */
                        return i;
@@ -733,11 +813,11 @@ unsigned run_ops(struct tdb_context *tdb,
 static struct op *maybe_cancel_transaction(const char *filename,
                                           struct op *op, unsigned int *num)
 {
-       unsigned int start = op_transaction_start(op, *num);
+       unsigned int start = op_find_start(op, *num, OP_TDB_TRANSACTION_START);
 
        if (start) {
                char *words[] = { "<unknown>", "tdb_close", NULL };
-               add_op(filename, &op, *num, op[start].serial,
+               add_op(filename, &op, *num, op[start].seqnum,
                       OP_TDB_TRANSACTION_CANCEL);
                op_analyze_transaction(filename, op, *num, words);
                (*num)++;
@@ -777,7 +857,7 @@ static struct op *load_tracefile(const char *filename, unsigned int *num,
 
                words = strsplit(lines, lines[i], " ", NULL);
                if (!words[0] || !words[1])
-                       fail(filename, i+1, "Expected serial number and op");
+                       fail(filename, i+1, "Expected seqnum number and op");
               
                opt = find_keyword(words[1], strlen(words[1]));
                if (!opt) {
@@ -805,15 +885,10 @@ static struct op *load_tracefile(const char *filename, unsigned int *num,
 }
 
 /* We remember all the keys we've ever seen, and who has them. */
-struct key_user {
-       unsigned int file;
-       unsigned int op_num;
-};
-
 struct keyinfo {
        TDB_DATA key;
        unsigned int num_users;
-       struct key_user *user;
+       struct op_desc *user;
 };
 
 static const TDB_DATA must_not_exist;
@@ -825,7 +900,7 @@ static const TDB_DATA not_exists_or_empty;
  * not exist, otherwise the data it needs. */
 static const TDB_DATA *needs(const struct op *op)
 {
-       switch (op->op) {
+       switch (op->type) {
        /* FIXME: Pull forward deps, since we can deadlock */
        case OP_TDB_CHAINLOCK:
        case OP_TDB_CHAINLOCK_NONBLOCK:
@@ -889,32 +964,66 @@ static const TDB_DATA *needs(const struct op *op)
                return &must_exist;
 
        default:
-               errx(1, "Unexpected op %i", op->op);
+               errx(1, "Unexpected op type %i", op->type);
        }
        
 }
 
-static bool is_transaction(const struct op *op)
+static bool starts_transaction(const struct op *op)
+{
+       return op->type == OP_TDB_TRANSACTION_START;
+}
+
+static bool in_transaction(const struct op op[], unsigned int i)
+{
+       return op[i].group_start && starts_transaction(&op[op[i].group_start]);
+}
+
+static bool successful_transaction(const struct op *op)
 {
-       return op->op == OP_TDB_TRANSACTION_START;
+       return starts_transaction(op)
+               && op[op->group_len].type == OP_TDB_TRANSACTION_COMMIT;
+}
+
+static bool starts_traverse(const struct op *op)
+{
+       return op->type == OP_TDB_TRAVERSE_START
+               || op->type == OP_TDB_TRAVERSE_READ_START;
+}
+
+static bool in_traverse(const struct op op[], unsigned int i)
+{
+       return op[i].group_start && starts_traverse(&op[op[i].group_start]);
+}
+
+static bool starts_chainlock(const struct op *op)
+{
+       return op->type == OP_TDB_CHAINLOCK_READ
+               || op->type == OP_TDB_CHAINLOCK;
+}
+
+static bool in_chainlock(const struct op op[], unsigned int i)
+{
+       return op[i].group_start && starts_chainlock(&op[op[i].group_start]);
 }
 
 /* What's the data after this op?  pre if nothing changed. */
 static const TDB_DATA *gives(const TDB_DATA *key, const TDB_DATA *pre,
                             const struct op *op)
 {
-       if (is_transaction(op)) {
+       if (starts_transaction(op) || starts_chainlock(op)) {
                unsigned int i;
 
                /* Cancelled transactions don't change anything. */
-               if (op[op->group_len].op == OP_TDB_TRANSACTION_CANCEL)
+               if (op[op->group_len].type == OP_TDB_TRANSACTION_CANCEL)
                        return pre;
-               assert(op[op->group_len].op == OP_TDB_TRANSACTION_COMMIT);
+               assert(op[op->group_len].type == OP_TDB_TRANSACTION_COMMIT
+                      || op[op->group_len].type == OP_TDB_CHAINUNLOCK_READ
+                      || op[op->group_len].type == OP_TDB_CHAINUNLOCK);
 
                for (i = 1; i < op->group_len; i++) {
                        /* This skips nested transactions, too */
-                       if (op[i].op != OP_TDB_TRAVERSE
-                           && key_eq(op[i].key, *key))
+                       if (key_eq(op[i].key, *key))
                                pre = gives(key, pre, &op[i]);
                }
                return pre;
@@ -924,28 +1033,18 @@ static const TDB_DATA *gives(const TDB_DATA *key, const TDB_DATA *pre,
        if (op->ret < 0)
                return pre;
 
-       if (op->op == OP_TDB_DELETE || op->op == OP_TDB_WIPE_ALL)
+       if (op->type == OP_TDB_DELETE || op->type == OP_TDB_WIPE_ALL)
                return &tdb_null;
 
-       if (op->op == OP_TDB_APPEND)
+       if (op->type == OP_TDB_APPEND)
                return &op->append.post;
 
-       if (op->op == OP_TDB_STORE)
+       if (op->type == OP_TDB_STORE)
                return &op->data;
 
        return pre;
 }
 
-static bool in_transaction(const struct op op[], unsigned int i)
-{
-       return op[i].group_start && is_transaction(&op[op[i].group_start]);
-}
-
-static bool in_traverse(const struct op op[], unsigned int i)
-{
-       return op[i].group_start && !is_transaction(&op[op[i].group_start]);
-}
-
 static struct keyinfo *hash_ops(struct op *op[], unsigned int num_ops[],
                                unsigned int num)
 {
@@ -962,11 +1061,6 @@ static struct keyinfo *hash_ops(struct op *op[], unsigned int num_ops[],
                        if (!op[i][j].key.dptr)
                                continue;
 
-                       /* We don't wait for traverse keys */
-                       /* FIXME: We should, for trivial traversals. */
-                       if (op[i][j].op == OP_TDB_TRAVERSE)
-                               continue;
-
                        h = hash_key(&op[i][j].key) % (total_keys * 2);
                        while (!key_eq(hash[h].key, op[i][j].key)) {
                                if (!hash[h].key.dptr) {
@@ -981,12 +1075,13 @@ static struct keyinfo *hash_ops(struct op *op[], unsigned int num_ops[],
                                op[i][j].key.dptr = hash[h].key.dptr;
                        }
                        hash[h].user = talloc_realloc(hash, hash[h].user,
-                                                    struct key_user,
+                                                    struct op_desc,
                                                     hash[h].num_users+1);
 
                        /* If it's in a transaction, it's the transaction which
                         * matters from an analysis POV. */
-                       if (in_transaction(op[i], j)) {
+                       if (in_transaction(op[i], j)
+                           || in_chainlock(op[i], j)) {
                                unsigned start = op[i][j].group_start;
 
                                /* Don't include twice. */
@@ -1013,14 +1108,13 @@ static bool satisfies(const TDB_DATA *key, const TDB_DATA *data,
 {
        const TDB_DATA *need = NULL;
 
-       if (is_transaction(op)) {
+       if (starts_transaction(op) || starts_chainlock(op)) {
                unsigned int i;
 
                /* Look through for an op in this transaction which
                 * needs this key. */
                for (i = 1; i < op->group_len; i++) {
-                       if (op[i].op != OP_TDB_TRAVERSE
-                           && key_eq(op[i].key, *key)) {
+                       if (key_eq(op[i].key, *key)) {
                                need = needs(&op[i]);
                                /* tdb_exists() is special: there might be
                                 * something in the transaction with more
@@ -1028,7 +1122,7 @@ static bool satisfies(const TDB_DATA *key, const TDB_DATA *data,
                                 * specific requirements (eg. store or delete),
                                 * but they change the value so we can't get
                                 * more information from future ops. */
-                               if (op[i].op != OP_TDB_EXISTS)
+                               if (op[i].type != OP_TDB_EXISTS)
                                        break;
                        }
                }
@@ -1060,26 +1154,26 @@ static bool satisfies(const TDB_DATA *key, const TDB_DATA *data,
        return key_eq(*data, *need);
 }
 
-static void move_to_front(struct key_user res[], unsigned off, unsigned elem)
+static void move_to_front(struct op_desc res[], unsigned off, unsigned elem)
 {
        if (elem != off) {
-               struct key_user tmp = res[elem];
+               struct op_desc tmp = res[elem];
                memmove(res + off + 1, res + off, (elem - off)*sizeof(res[0]));
                res[off] = tmp;
        }
 }
 
-static void restore_to_pos(struct key_user res[], unsigned off, unsigned elem)
+static void restore_to_pos(struct op_desc res[], unsigned off, unsigned elem)
 {
        if (elem != off) {
-               struct key_user tmp = res[off];
+               struct op_desc tmp = res[off];
                memmove(res + off, res + off + 1, (elem - off)*sizeof(res[0]));
                res[elem] = tmp;
        }
 }
 
 static bool sort_deps(char *filename[], struct op *op[],
-                     struct key_user res[],
+                     struct op_desc res[],
                      unsigned off, unsigned num,
                      const TDB_DATA *key, const TDB_DATA *data,
                      unsigned num_files, unsigned fuzz)
@@ -1088,30 +1182,30 @@ static bool sort_deps(char *filename[], struct op *op[],
        struct op *this_op;
        bool done[num_files];
 
-       /* Does this make serial numbers go backwards?  Allow a little fuzz. */
+       /* None left?  We're sorted. */
+       if (off == num)
+               return true;
+
+       /* Does this make sequence number go backwards?  Allow a little fuzz. */
        if (off > 0) {
-               int serial1 = op[res[off-1].file][res[off-1].op_num].serial;
-               int serial2 = op[res[off].file][res[off].op_num].serial;
+               int seqnum1 = op[res[off-1].file][res[off-1].op_num].seqnum;
+               int seqnum2 = op[res[off].file][res[off].op_num].seqnum;
 
-               if (serial1 - serial2 > (int)fuzz) {
+               if (seqnum1 - seqnum2 > (int)fuzz) {
 #if DEBUG_DEPS
-                       printf("Serial jump too far (%u -> %u)\n",
-                              serial1, serial2);
+                       printf("Seqnum jump too far (%u -> %u)\n",
+                              seqnum1, seqnum2);
 #endif
                        return false;
                }
        }
 
-       /* One or none left?  We're sorted. */
-       if (off + 1 >= num)
-               return true;
-
        memset(done, 0, sizeof(done));
 
        /* Since ops within a trace file are ordered, we just need to figure
         * out which file to try next.  Since we don't take into account
         * inter-key relationships (which exist by virtue of trace file order),
-        * we minimize the chance of harm by trying to keep in serial order. */
+        * we minimize the chance of harm by trying to keep in seqnum order. */
        for (files_done = 0, i = off; i < num && files_done < num_files; i++) {
                if (done[res[i].file])
                        continue;
@@ -1135,7 +1229,7 @@ static bool sort_deps(char *filename[], struct op *op[],
        return false;
 }
 
-static void check_dep_sorting(struct key_user user[], unsigned num_users,
+static void check_dep_sorting(struct op_desc user[], unsigned num_users,
                              unsigned num_files)
 {
 #if DEBUG_DEPS
@@ -1153,19 +1247,19 @@ static void check_dep_sorting(struct key_user user[], unsigned num_users,
 /* All these ops happen on the same key.  Which comes first?
  *
  * This can happen both because read ops or failed write ops don't
- * change serial number, and also due to race since we access the
+ * change sequence number, and also due to race since we access the
  * number unlocked (the race can cause less detectable ordering problems,
  * in which case we'll deadlock and report: fix manually in that case).
  */
 static void figure_deps(char *filename[], struct op *op[],
-                       const TDB_DATA *key, struct key_user user[],
+                       const TDB_DATA *key, struct op_desc user[],
                        unsigned num_users, unsigned num_files)
 {
        /* We assume database starts empty. */
        const struct TDB_DATA *data = &tdb_null;
        unsigned int fuzz;
 
-       /* We prefer to keep strict serial order if possible: it's the
+       /* We prefer to keep strict seqnum order if possible: it's the
         * most likely.  We get more lax if that fails. */
        for (fuzz = 0; fuzz < 100; fuzz = (fuzz + 1)*2) {
                if (sort_deps(filename, op, user, 0, num_users, key, data,
@@ -1186,24 +1280,37 @@ static void sort_ops(struct keyinfo hash[], char *filename[], struct op *op[],
        unsigned int h;
 
        /* Gcc nexted function extension.  How cool is this? */
-       int compare_serial(const void *_a, const void *_b)
+       int compare_seqnum(const void *_a, const void *_b)
        {
-               const struct key_user *a = _a, *b = _b;
+               const struct op_desc *a = _a, *b = _b;
 
                /* First, maintain order within any trace file. */
                if (a->file == b->file)
                        return a->op_num - b->op_num;
 
-               /* Otherwise, arrange by serial order. */
-               return op[a->file][a->op_num].serial
-                       - op[b->file][b->op_num].serial;
+               /* Otherwise, arrange by seqnum order. */
+               if (op[a->file][a->op_num].seqnum !=
+                   op[b->file][b->op_num].seqnum)
+                       return op[a->file][a->op_num].seqnum
+                               - op[b->file][b->op_num].seqnum;
+
+               /* Cancelled transactions are assumed to happen first. */
+               if (starts_transaction(&op[a->file][a->op_num])
+                   && !successful_transaction(&op[a->file][a->op_num]))
+                       return -1;
+               if (starts_transaction(&op[b->file][b->op_num])
+                   && !successful_transaction(&op[b->file][b->op_num]))
+                       return 1;
+
+               /* No idea. */
+               return 0;
        }
 
-       /* Now sort into serial order. */
+       /* Now sort into seqnum order. */
        for (h = 0; h < total_keys * 2; h++) {
-               struct key_user *user = hash[h].user;
+               struct op_desc *user = hash[h].user;
 
-               qsort(user, hash[h].num_users, sizeof(user[0]), compare_serial);
+               qsort(user, hash[h].num_users, sizeof(user[0]), compare_seqnum);
                figure_deps(filename, op, &hash[h].key, user, hash[h].num_users,
                            num);
        }
@@ -1219,40 +1326,44 @@ static int destroy_depend(struct depend *dep)
 static void add_dependency(void *ctx,
                           struct op *op[],
                           char *filename[],
-                          unsigned int needs_file,
-                          unsigned int needs_opnum,
-                          unsigned int satisfies_file,
-                          unsigned int satisfies_opnum)
+                          const struct op_desc *needs,
+                          const struct op_desc *prereq)
 {
        struct depend *dep;
 
        /* We don't depend on ourselves. */
-       if (needs_file == satisfies_file) {
-               assert(satisfies_opnum < needs_opnum);
+       if (needs->file == prereq->file) {
+               assert(prereq->op_num < needs->op_num);
                return;
        }
 
 #if DEBUG_DEPS
        printf("%s:%u: depends on %s:%u\n",
-              filename[needs_file], needs_opnum+1,
-              filename[satisfies_file], satisfies_opnum+1);
+              filename[needs->file], needs->op_num+1,
+              filename[prereq->file], prereq->op_num+1);
 #endif
 
+       dep = talloc(ctx, struct depend);
+       dep->needs = *needs;
+       dep->prereq = *prereq;
+
 #if TRAVERSALS_TAKE_TRANSACTION_LOCK
        /* If something in a traverse depends on something in another
         * traverse/transaction, it creates a dependency between the
         * two groups. */
-       if ((in_traverse(op[satisfies_file], satisfies_opnum)
-            && op[needs_file][needs_opnum].group_start)
-           || (in_traverse(op[needs_file], needs_opnum)
-               && op[satisfies_file][satisfies_opnum].group_start)) {
-               unsigned int sat;
+       if ((in_traverse(op[prereq->file], prereq->op_num)
+            && (starts_transaction(&op[needs->file][needs->op_num])
+                || starts_traverse(&op[needs->file][needs->op_num])))
+           || (in_traverse(op[needs->file], needs->op_num)
+               && (starts_transaction(&op[prereq->file][prereq->op_num])
+                   || starts_traverse(&op[prereq->file][prereq->op_num])))) {
+               unsigned int start;
 
                /* We are satisfied by end of group. */
-               sat = op[satisfies_file][satisfies_opnum].group_start;
-               satisfies_opnum = sat + op[satisfies_file][sat].group_len;
+               start = op[prereq->file][prereq->op_num].group_start;
+               dep->prereq.op_num = start + op[prereq->file][start].group_len;
                /* And we need that done by start of our group. */
-               needs_opnum = op[needs_file][needs_opnum].group_start;
+               dep->needs.op_num = op[needs->file][needs->op_num].group_start;
        }
 
        /* There is also this case:
@@ -1264,42 +1375,38 @@ static void add_dependency(void *ctx,
         * We try to address this by ensuring that where seqnum indicates it's
         * possible, we wait for <create foo> before *starting* traverse.
         */
-       else if (in_traverse(op[needs_file], needs_opnum)) {
-               struct op *need = &op[needs_file][needs_opnum];
-               if (op[needs_file][need->group_start].serial >
-                   op[satisfies_file][satisfies_opnum].serial) {
-                       needs_opnum = need->group_start;
+       else if (in_traverse(op[needs->file], needs->op_num)) {
+               struct op *need = &op[needs->file][needs->op_num];
+               if (op[needs->file][need->group_start].seqnum >
+                   op[prereq->file][prereq->op_num].seqnum) {
+                       dep->needs.op_num = need->group_start;
                }
        }
 #endif
 
-       /* If you depend on a transaction, you actually depend on it ending. */
-       if (is_transaction(&op[satisfies_file][satisfies_opnum])) {
-               satisfies_opnum
-                       += op[satisfies_file][satisfies_opnum].group_len;
+       /* If you depend on a transaction or chainlock, you actually
+        * depend on it ending. */
+       if (starts_transaction(&op[prereq->file][dep->prereq.op_num])
+           || starts_chainlock(&op[prereq->file][dep->prereq.op_num])) {
+               dep->prereq.op_num
+                       += op[dep->prereq.file][dep->prereq.op_num].group_len;
 #if DEBUG_DEPS
                printf("-> Actually end of transaction %s:%u\n",
-                      filename[satisfies_file], satisfies_opnum+1);
+                      filename[dep->prereq->file], dep->prereq->op_num+1);
 #endif
        } else
                /* We should never create a dependency from middle of
                 * a transaction. */
-               assert(!in_transaction(op[satisfies_file], satisfies_opnum)
-                      || op[satisfies_file][satisfies_opnum].op
+               assert(!in_transaction(op[prereq->file], dep->prereq.op_num)
+                      || op[prereq->file][dep->prereq.op_num].type
                       == OP_TDB_TRANSACTION_COMMIT
-                      || op[satisfies_file][satisfies_opnum].op
+                      || op[prereq->file][dep->prereq.op_num].type
                       == OP_TDB_TRANSACTION_CANCEL);
 
-       assert(op[needs_file][needs_opnum].op != OP_TDB_TRAVERSE);
-       assert(op[satisfies_file][satisfies_opnum].op != OP_TDB_TRAVERSE);
-
-       dep = talloc(ctx, struct depend);
-       dep->needs_file = needs_file;
-       dep->needs_opnum = needs_opnum;
-       dep->satisfies_file = satisfies_file;
-       dep->satisfies_opnum = satisfies_opnum;
-       list_add(&op[satisfies_file][satisfies_opnum].post, &dep->post_list);
-       list_add(&op[needs_file][needs_opnum].pre, &dep->pre_list);
+       list_add(&op[dep->prereq.file][dep->prereq.op_num].post,
+                &dep->post_list);
+       list_add(&op[dep->needs.file][dep->needs.op_num].pre,
+                &dep->pre_list);
        talloc_set_destructor(dep, destroy_depend);
 }
 
@@ -1311,7 +1418,7 @@ static bool changes_db(const TDB_DATA *key, const struct op *op)
 static void depend_on_previous(struct op *op[],
                               char *filename[],
                               unsigned int num,
-                              struct key_user user[],
+                              struct op_desc user[],
                               unsigned int i,
                               int prev)
 {
@@ -1323,9 +1430,7 @@ static void depend_on_previous(struct op *op[],
 
        if (prev == i - 1) {
                /* Just depend on previous. */
-               add_dependency(NULL, op, filename,
-                              user[i].file, user[i].op_num,
-                              user[prev].file, user[prev].op_num);
+               add_dependency(NULL, op, filename, &user[i], &user[prev]);
                return;
        }
 
@@ -1334,9 +1439,7 @@ static void depend_on_previous(struct op *op[],
        deps[user[i].file] = true;
        for (j = i - 1; j > prev; j--) {
                if (!deps[user[j].file]) {
-                       add_dependency(NULL, op, filename,
-                                      user[i].file, user[i].op_num,
-                                      user[j].file, user[j].op_num);
+                       add_dependency(NULL, op, filename, &user[i], &user[j]);
                        deps[user[j].file] = true;
                }
        }
@@ -1358,14 +1461,14 @@ static void optimize_dependencies(struct op *op[], unsigned int num_ops[],
                        memset(prev, 0, sizeof(prev));
 
                        list_for_each_safe(&op[i][j].pre, dep, next, pre_list) {
-                               if (!prev[dep->satisfies_file]) {
-                                       prev[dep->satisfies_file] = dep;
+                               if (!prev[dep->prereq.file]) {
+                                       prev[dep->prereq.file] = dep;
                                        continue;
                                }
-                               if (prev[dep->satisfies_file]->satisfies_opnum
-                                   < dep->satisfies_opnum) {
-                                       talloc_free(prev[dep->satisfies_file]);
-                                       prev[dep->satisfies_file] = dep;
+                               if (prev[dep->prereq.file]->prereq.op_num
+                                   < dep->prereq.op_num) {
+                                       talloc_free(prev[dep->prereq.file]);
+                                       prev[dep->prereq.file] = dep;
                                } else
                                        talloc_free(dep);
                        }
@@ -1382,17 +1485,130 @@ static void optimize_dependencies(struct op *op[], unsigned int num_ops[],
                        struct depend *dep, *next;
 
                        list_for_each_safe(&op[i][j].pre, dep, next, pre_list) {
-                               if (deps[dep->satisfies_file]
-                                   >= (int)dep->satisfies_opnum)
+                               if (deps[dep->prereq.file]
+                                   >= (int)dep->prereq.op_num)
                                        talloc_free(dep);
                                else
-                                       deps[dep->satisfies_file]
-                                               = dep->satisfies_opnum;
+                                       deps[dep->prereq.file]
+                                               = dep->prereq.op_num;
                        }
                }
        }
 }
 
+#if TRAVERSALS_TAKE_TRANSACTION_LOCK
+/* Force an order among the traversals, so they don't deadlock (as much) */
+static void make_traverse_depends(char *filename[],
+                                 struct op *op[], unsigned int num_ops[],
+                                 unsigned int num)
+{
+       unsigned int i, num_traversals = 0;
+       int j;
+       struct op_desc *desc;
+
+       /* Sort by which one runs first. */
+       int compare_traverse_desc(const void *_a, const void *_b)
+       {
+               const struct op_desc *da = _a, *db = _b;
+               const struct op *a = &op[da->file][da->op_num],
+                       *b = &op[db->file][db->op_num];
+
+               if (a->seqnum != b->seqnum)
+                       return a->seqnum - b->seqnum;
+
+               /* If they have same seqnum, it means one didn't make any
+                * changes.  Thus sort by end in that case. */
+               return a[a->group_len].seqnum - b[b->group_len].seqnum;
+       }
+
+       desc = talloc_array(NULL, struct op_desc, 1);
+
+       /* Count them. */
+       for (i = 0; i < num; i++) {
+               for (j = 1; j < num_ops[i]; j++) {
+                       /* Traverse start (ignore those in
+                        * transactions; they're already covered by
+                        * transaction dependencies). */
+                       if (starts_traverse(&op[i][j])
+                           && !in_transaction(op[i], j)) {
+                               desc = talloc_realloc(NULL, desc,
+                                                     struct op_desc,
+                                                     num_traversals+1);
+                               desc[num_traversals].file = i;
+                               desc[num_traversals].op_num = j;
+                               num_traversals++;
+                       }
+               }
+       }
+       qsort(desc, num_traversals, sizeof(desc[0]), compare_traverse_desc);
+
+       for (i = 1; i < num_traversals; i++) {
+               const struct op *prev = &op[desc[i-1].file][desc[i-1].op_num];
+               const struct op *curr = &op[desc[i].file][desc[i].op_num];
+
+               /* Read traverses don't depend on each other (read lock). */
+               if (prev->type == OP_TDB_TRAVERSE_READ_START
+                   && curr->type == OP_TDB_TRAVERSE_READ_START)
+                       continue;
+
+               /* Only make dependency if it's clear. */
+               if (compare_traverse_desc(&desc[i], &desc[i-1])) {
+                       /* i depends on end of traverse i-1. */
+                       struct op_desc end = desc[i-1];
+                       end.op_num += prev->group_len;
+                       add_dependency(NULL, op, filename, &desc[i], &end);
+               }
+       }
+       talloc_free(desc);
+}
+
+static void set_nonblock(int fd)
+{
+       if (fcntl(fd, F_SETFL, fcntl(fd, F_GETFL)|O_NONBLOCK) != 0)
+               err(1, "Setting pipe nonblocking");
+}
+
+static bool handle_backoff(struct op *op[], int fd)
+{
+       struct op_desc desc;
+       bool handled = false;
+
+       /* Sloppy coding: we assume PIPEBUF never fills. */
+       while (read(fd, &desc, sizeof(desc)) != -1) {
+               unsigned int i;
+               handled = true;
+               for (i = desc.op_num; i > 0; i--) {
+                       if (op[desc.file][i].type == OP_TDB_TRAVERSE) {
+                               /* We insert a fake end here. */
+                               op[desc.file][i].type
+                                       = OP_TDB_TRAVERSE_END_EARLY;
+                               break;
+                       } else if (starts_traverse(&op[desc.file][i])) {
+                               unsigned int start = i;
+                               struct op tmp = op[desc.file][i];
+                               /* Move the ops outside traverse. */
+                               memmove(&op[desc.file][i],
+                                       &op[desc.file][i+1],
+                                       (desc.op_num-i-1) * sizeof(op[0][0]));
+                               op[desc.file][desc.op_num] = tmp;
+                               while (op[desc.file][i].group_start == start) {
+                                       op[desc.file][i++].group_start
+                                               = desc.op_num;
+                               }
+                               break;
+                       }
+               }
+       }
+       return handled;
+}
+
+#else /* !TRAVERSALS_TAKE_TRANSACTION_LOCK */
+static bool handle_backoff(struct op *op[], int fd)
+{
+       return false;
+}
+#endif
+
 static void derive_dependencies(char *filename[],
                                struct op *op[], unsigned int num_ops[],
                                unsigned int num)
@@ -1403,7 +1619,7 @@ static void derive_dependencies(char *filename[],
        /* Create hash table for faster key lookup. */
        hash = hash_ops(op, num_ops, num);
 
-       /* Sort them by serial number. */
+       /* Sort them by sequence number. */
        sort_ops(hash, filename, op, num);
 
        /* Create dependencies back to the last change, rather than
@@ -1428,65 +1644,33 @@ static void derive_dependencies(char *filename[],
                                prev = i;
                        } else if (prev >= 0)
                                add_dependency(hash, op, filename,
-                                              hash[h].user[i].file,
-                                              hash[h].user[i].op_num,
-                                              hash[h].user[prev].file,
-                                              hash[h].user[prev].op_num);
+                                              &hash[h].user[i],
+                                              &hash[h].user[prev]);
                }
        }
 
+#if TRAVERSALS_TAKE_TRANSACTION_LOCK
+       make_traverse_depends(filename, op, num_ops, num);
+#endif
+
        optimize_dependencies(op, num_ops, num);
 }
 
-int main(int argc, char *argv[])
+static struct timeval run_test(char *argv[],
+                              unsigned int num_ops[],
+                              unsigned int hashsize[],
+                              unsigned int tdb_flags[],
+                              unsigned int open_flags[],
+                              struct op *op[],
+                              int fds[2])
 {
-       struct timeval start, end;
-       unsigned int i, num_ops[argc], hashsize[argc], tdb_flags[argc], open_flags[argc];
-       struct op *op[argc];
-       int fds[2];
-       char c;
+       unsigned int i;
+       struct timeval start, end, diff;
        bool ok = true;
 
-       if (argc < 3)
-               errx(1, "Usage: %s <tdbfile> <tracefile>...", argv[0]);
-
-       pipes = talloc_array(NULL, struct pipe, argc - 2);
-       for (i = 0; i < argc - 2; i++) {
-               printf("Loading tracefile %s...", argv[2+i]);
-               fflush(stdout);
-               op[i] = load_tracefile(argv[2+i], &num_ops[i], &hashsize[i],
-                                      &tdb_flags[i], &open_flags[i]);
-               if (pipe(pipes[i].fd) != 0)
-                       err(1, "creating pipe");
-               printf("done\n");
-       }
-
-       printf("Calculating inter-dependencies...");
-       fflush(stdout);
-       derive_dependencies(argv+2, op, num_ops, i);
-       printf("done\n");
-
-       /* Don't fork for single arg case: simple debugging. */
-       if (argc == 3) {
-               struct tdb_context *tdb;
-               tdb = tdb_open_ex(argv[1], hashsize[0], tdb_flags[0]|TDB_NOSYNC,
-                                 open_flags[0], 0600, NULL, hash_key);
-               printf("Single threaded run...");
-               fflush(stdout);
-
-               run_ops(tdb, pipes[0].fd[0], argv+2, op, 0, 1, num_ops[0],
-                       false);
-               check_deps(argv[2], op[0], num_ops[0]);
-
-               printf("done\n");
-               exit(0);
-       }
-
-       if (pipe(fds) != 0)
-               err(1, "creating pipe");
-
-       for (i = 0; i < argc - 2; i++) {
+       for (i = 0; argv[i+2]; i++) {
                struct tdb_context *tdb;
+               char c;
 
                switch (fork()) {
                case -1:
@@ -1521,7 +1705,7 @@ int main(int argc, char *argv[])
        if (write(fds[1], hashsize, i) != i)
                err(1, "Writing to wakeup pipe");
 
-       for (i = 0; i < argc - 2; i++) {
+       for (i = 0; argv[i + 2]; i++) {
                int status;
                wait(&status);
                if (!WIFEXITED(status)) {
@@ -1537,9 +1721,75 @@ int main(int argc, char *argv[])
        gettimeofday(&end, NULL);
        printf("done\n");
 
-       end.tv_sec -= start.tv_sec;
+       if (end.tv_usec < start.tv_usec) {
+               end.tv_usec += 1000000;
+               end.tv_sec--;
+       }
+       diff.tv_sec = end.tv_sec - start.tv_sec;
+       diff.tv_usec = end.tv_usec - start.tv_usec;
+       return diff;
+}
+
+int main(int argc, char *argv[])
+{
+       struct timeval diff;
+       unsigned int i, num_ops[argc], hashsize[argc], tdb_flags[argc], open_flags[argc];
+       struct op *op[argc];
+       int fds[2];
+
+       if (argc < 3)
+               errx(1, "Usage: %s <tdbfile> <tracefile>...", argv[0]);
+
+       pipes = talloc_array(NULL, struct pipe, argc - 1);
+       for (i = 0; i < argc - 2; i++) {
+               printf("Loading tracefile %s...", argv[2+i]);
+               fflush(stdout);
+               op[i] = load_tracefile(argv[2+i], &num_ops[i], &hashsize[i],
+                                      &tdb_flags[i], &open_flags[i]);
+               if (pipe(pipes[i].fd) != 0)
+                       err(1, "creating pipe");
+               printf("done\n");
+       }
+
+       printf("Calculating inter-dependencies...");
+       fflush(stdout);
+       derive_dependencies(argv+2, op, num_ops, i);
+       printf("done\n");
+
+       /* Don't fork for single arg case: simple debugging. */
+       if (argc == 3) {
+               struct tdb_context *tdb;
+               tdb = tdb_open_ex(argv[1], hashsize[0], tdb_flags[0]|TDB_NOSYNC,
+                                 open_flags[0], 0600, NULL, hash_key);
+               printf("Single threaded run...");
+               fflush(stdout);
+
+               run_ops(tdb, pipes[0].fd[0], argv+2, op, 0, 1, num_ops[0],
+                       false);
+               check_deps(argv[2], op[0], num_ops[0]);
+
+               printf("done\n");
+               exit(0);
+       }
+
+       if (pipe(fds) != 0)
+               err(1, "creating pipe");
+
+#if TRAVERSALS_TAKE_TRANSACTION_LOCK
+       if (pipe(pipes[argc-2].fd) != 0)
+               err(1, "creating pipe");
+       backoff_fd = pipes[argc-2].fd[1];
+       set_nonblock(pipes[argc-2].fd[1]);
+       set_nonblock(pipes[argc-2].fd[0]);
+#endif
+
+       do {
+               diff = run_test(argv, num_ops, hashsize, tdb_flags, open_flags,
+                               op, fds);
+       } while (handle_backoff(op, pipes[argc-2].fd[0]));
+
        printf("Time replaying: %lu usec\n",
-              end.tv_sec * 1000000UL + (end.tv_usec - start.tv_usec));
+              diff.tv_sec * 1000000UL + diff.tv_usec);
        
        exit(0);
 }