X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=ovsdb%2Ftransaction.c;h=bfa2fcbad65c20dc1cc59640be6596596fd4a6f1;hb=88cd3cc9f41f916fd51ad1cd02cbbfb50d9b476d;hp=137ae06b7c9bffe383ab36b96881b4ff208076ff;hpb=c69ee87c10818267f991236201150b1fa51ae519;p=sliver-openvswitch.git

diff --git a/ovsdb/transaction.c b/ovsdb/transaction.c
index 137ae06b7..bfa2fcbad 100644
--- a/ovsdb/transaction.c
+++ b/ovsdb/transaction.c
@@ -19,6 +19,7 @@
 
 #include <assert.h>
 
+#include "bitmap.h"
 #include "dynamic-string.h"
 #include "hash.h"
 #include "hmap.h"
@@ -41,6 +42,10 @@ struct ovsdb_txn_table {
     struct list node;           /* Element in ovsdb_txn's txn_tables list. */
     struct ovsdb_table *table;
     struct hmap txn_rows;       /* Contains "struct ovsdb_txn_row"s. */
+
+    /* Used by for_each_txn_row(). */
+    unsigned int serial;        /* Serial number of in-progress iteration. */
+    unsigned int n_processed;   /* Number of rows processed. */
 };
 
 /* A row modified by the transaction:
@@ -60,8 +65,24 @@ struct ovsdb_txn_row {
     struct hmap_node hmap_node; /* In ovsdb_txn_table's txn_rows hmap. */
     struct ovsdb_row *old;      /* The old row. */
     struct ovsdb_row *new;      /* The new row. */
+    size_t n_refs;              /* Number of remaining references. */
+
+    /* Used by for_each_txn_row(). */
+    unsigned int serial;        /* Serial number of in-progress commit. */
+
+    unsigned long changed[];    /* Bits set to 1 for columns that changed. */
 };
 
+static void ovsdb_txn_row_prefree(struct ovsdb_txn_row *);
+static struct ovsdb_error * WARN_UNUSED_RESULT
+for_each_txn_row(struct ovsdb_txn *txn,
+                      struct ovsdb_error *(*)(struct ovsdb_txn *,
+                                              struct ovsdb_txn_row *));
+
+/* Used by for_each_txn_row() to track tables and rows that have been
+ * processed.  */
+static unsigned int serial;
+
 struct ovsdb_txn *
 ovsdb_txn_create(struct ovsdb *db)
 {
@@ -73,42 +94,21 @@ ovsdb_txn_create(struct ovsdb *db)
 }
 
 static void
-ovsdb_txn_destroy(struct ovsdb_txn *txn, void (*cb)(struct ovsdb_txn_row *))
+ovsdb_txn_free(struct ovsdb_txn *txn)
 {
-    struct ovsdb_txn_table *txn_table, *next_txn_table;
-
-    LIST_FOR_EACH_SAFE (txn_table, next_txn_table,
-                        struct ovsdb_txn_table, node, &txn->txn_tables) {
-        struct ovsdb_txn_row *txn_row, *next_txn_row;
-
-        HMAP_FOR_EACH_SAFE (txn_row, next_txn_row,
-                            struct ovsdb_txn_row, hmap_node,
-                            &txn_table->txn_rows)
-        {
-            if (txn_row->old) {
-                txn_row->old->txn_row = NULL;
-            }
-            if (txn_row->new) {
-                txn_row->new->txn_row = NULL;
-            }
-            cb(txn_row);
-            free(txn_row);
-        }
-
-        txn_table->table->txn_table = NULL;
-        hmap_destroy(&txn_table->txn_rows);
-        free(txn_table);
-    }
+    assert(list_is_empty(&txn->txn_tables));
     ds_destroy(&txn->comment);
     free(txn);
 }
 
-static void
-ovsdb_txn_row_abort(struct ovsdb_txn_row *txn_row)
+static struct ovsdb_error *
+ovsdb_txn_row_abort(struct ovsdb_txn *txn OVS_UNUSED,
+                    struct ovsdb_txn_row *txn_row)
 {
     struct ovsdb_row *old = txn_row->old;
     struct ovsdb_row *new = txn_row->new;
 
+    ovsdb_txn_row_prefree(txn_row);
     if (!old) {
         hmap_remove(&new->table->rows, &new->hmap_node);
     } else if (!new) {
@@ -117,18 +117,16 @@ ovsdb_txn_row_abort(struct ovsdb_txn_row *txn_row)
         hmap_replace(&new->table->rows, &new->hmap_node, &old->hmap_node);
     }
     ovsdb_row_destroy(new);
+    free(txn_row);
+
+    return NULL;
 }
 
 void
 ovsdb_txn_abort(struct ovsdb_txn *txn)
 {
-    ovsdb_txn_destroy(txn, ovsdb_txn_row_abort);
-}
-
-static void
-ovsdb_txn_row_commit(struct ovsdb_txn_row *txn_row)
-{
-    ovsdb_row_destroy(txn_row->old);
+    ovsdb_error_assert(for_each_txn_row(txn, ovsdb_txn_row_abort));
+    ovsdb_txn_free(txn);
 }
 
 static struct ovsdb_txn_row *
@@ -153,129 +151,316 @@ find_txn_row(const struct ovsdb_table *table, const struct uuid *uuid)
     return NULL;
 }
 
-static void
-ovsdb_txn_adjust_atom_refs(const union ovsdb_atom *atoms, unsigned int n,
-                           const struct ovsdb_table *table,
-                           int delta, struct ovsdb_error **errorp)
+static struct ovsdb_error * WARN_UNUSED_RESULT
+ovsdb_txn_adjust_atom_refs(struct ovsdb_txn *txn, const struct ovsdb_row *r,
+                           const struct ovsdb_column *c,
+                           const struct ovsdb_base_type *base,
+                           const union ovsdb_atom *atoms, unsigned int n,
+                           int delta)
 {
+    const struct ovsdb_table *table;
     unsigned int i;
 
+    if (!ovsdb_base_type_is_strong_ref(base)) {
+        return NULL;
+    }
+
+    table = base->u.uuid.refTable;
     for (i = 0; i < n; i++) {
         const struct uuid *uuid = &atoms[i].uuid;
         struct ovsdb_txn_row *txn_row = find_txn_row(table, uuid);
-        if (txn_row) {
-            if (txn_row->old) {
-                txn_row->old->n_refs += delta;
-            }
-            if (txn_row->new) {
-                txn_row->new->n_refs += delta;
-            }
-        } else {
-            const struct ovsdb_row *row_ = ovsdb_table_get_row(table, uuid);
-            if (row_) {
-                struct ovsdb_row *row = (struct ovsdb_row *) row_;
-                row->n_refs += delta;
-            } else if (errorp) {
-                if (!*errorp) {
-                    *errorp = ovsdb_error("referential integrity violation",
-                                          "reference to nonexistent row "
-                                          UUID_FMT, UUID_ARGS(uuid));
-                }
+        if (!txn_row) {
+            const struct ovsdb_row *row = ovsdb_table_get_row(table, uuid);
+            if (row) {
+                txn_row = ovsdb_txn_row_modify(txn, row)->txn_row;
             } else {
-                NOT_REACHED();
+                return ovsdb_error("referential integrity violation",
+                                   "Table %s column %s row "UUID_FMT" "
+                                   "references nonexistent row "UUID_FMT" in "
+                                   "table %s.",
+                                   r->table->schema->name, c->name,
+                                   UUID_ARGS(ovsdb_row_get_uuid(r)),
+                                   UUID_ARGS(uuid), table->schema->name);
             }
         }
+        txn_row->n_refs += delta;
     }
+
+    return NULL;
 }
 
-static void
-ovsdb_txn_adjust_row_refs(const struct ovsdb_row *r,
-                          const struct ovsdb_column *column, int delta,
-                          struct ovsdb_error **errorp)
+static struct ovsdb_error * WARN_UNUSED_RESULT
+ovsdb_txn_adjust_row_refs(struct ovsdb_txn *txn, const struct ovsdb_row *r,
+                          const struct ovsdb_column *column, int delta)
 {
     const struct ovsdb_datum *field = &r->fields[column->index];
-    const struct ovsdb_type *type = &column->type;
+    struct ovsdb_error *error;
 
-    if (type->key.type == OVSDB_TYPE_UUID && type->key.u.uuid.refTable) {
-        ovsdb_txn_adjust_atom_refs(field->keys, field->n,
-                                   type->key.u.uuid.refTable, delta, errorp);
+    error = ovsdb_txn_adjust_atom_refs(txn, r, column, &column->type.key,
+                                       field->keys, field->n, delta);
+    if (!error) {
+        error = ovsdb_txn_adjust_atom_refs(txn, r, column, &column->type.value,
+                                           field->values, field->n, delta);
     }
-    if (type->value.type == OVSDB_TYPE_UUID && type->value.u.uuid.refTable) {
-        ovsdb_txn_adjust_atom_refs(field->values, field->n,
-                                   type->value.u.uuid.refTable, delta, errorp);
+    return error;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+update_row_ref_count(struct ovsdb_txn *txn, struct ovsdb_txn_row *r)
+{
+    struct ovsdb_table *table = r->old ? r->old->table : r->new->table;
+    struct shash_node *node;
+
+    SHASH_FOR_EACH (node, &table->schema->columns) {
+        const struct ovsdb_column *column = node->data;
+        struct ovsdb_error *error;
+
+        if (r->old) {
+            error = ovsdb_txn_adjust_row_refs(txn, r->old, column, -1);
+            if (error) {
+                ovsdb_error_destroy(error);
+                return OVSDB_BUG("error decreasing refcount");
+            }
+        }
+        if (r->new) {
+            error = ovsdb_txn_adjust_row_refs(txn, r->new, column, 1);
+            if (error) {
+                return error;
+            }
+        }
     }
+
+    return NULL;
 }
 
 static struct ovsdb_error * WARN_UNUSED_RESULT
-ovsdb_txn_adjust_ref_counts__(struct ovsdb_txn *txn, int delta)
+check_ref_count(struct ovsdb_txn *txn OVS_UNUSED, struct ovsdb_txn_row *r)
+{
+    if (r->new || !r->n_refs) {
+        return NULL;
+    } else {
+        return ovsdb_error("referential integrity violation",
+                           "cannot delete %s row "UUID_FMT" because "
+                           "of %zu remaining reference(s)",
+                           r->old->table->schema->name,
+                           UUID_ARGS(ovsdb_row_get_uuid(r->old)),
+                           r->n_refs);
+    }
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+update_ref_counts(struct ovsdb_txn *txn)
 {
-    struct ovsdb_txn_table *t;
     struct ovsdb_error *error;
 
-    error = NULL;
-    LIST_FOR_EACH (t, struct ovsdb_txn_table, node, &txn->txn_tables) {
-        struct ovsdb_table *table = t->table;
-        struct ovsdb_txn_row *r;
+    error = for_each_txn_row(txn, update_row_ref_count);
+    if (error) {
+        return error;
+    }
 
-        HMAP_FOR_EACH (r, struct ovsdb_txn_row, hmap_node, &t->txn_rows) {
-            struct shash_node *node;
+    return for_each_txn_row(txn, check_ref_count);
+}
+
+static struct ovsdb_error *
+ovsdb_txn_row_commit(struct ovsdb_txn *txn OVS_UNUSED,
+                     struct ovsdb_txn_row *txn_row)
+{
+    ovsdb_txn_row_prefree(txn_row);
+    if (txn_row->new) {
+        txn_row->new->n_refs = txn_row->n_refs;
+    }
+    ovsdb_row_destroy(txn_row->old);
+    free(txn_row);
+
+    return NULL;
+}
+
+static void
+add_weak_ref(struct ovsdb_txn *txn,
+             const struct ovsdb_row *src_, const struct ovsdb_row *dst_)
+{
+    struct ovsdb_row *src = (struct ovsdb_row *) src_;
+    struct ovsdb_row *dst = (struct ovsdb_row *) dst_;
+    struct ovsdb_weak_ref *weak;
+
+    if (src == dst) {
+        return;
+    }
+
+    dst = ovsdb_txn_row_modify(txn, dst);
+
+    if (!list_is_empty(&dst->dst_refs)) {
+        /* Omit duplicates. */
+        weak = CONTAINER_OF(list_back(&dst->dst_refs),
+                            struct ovsdb_weak_ref, dst_node);
+        if (weak->src == src) {
+            return;
+        }
+    }
+
+    weak = xmalloc(sizeof *weak);
+    weak->src = src;
+    list_push_back(&dst->dst_refs, &weak->dst_node);
+    list_push_back(&src->src_refs, &weak->src_node);
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+assess_weak_refs(struct ovsdb_txn *txn, struct ovsdb_txn_row *txn_row)
+{
+    struct ovsdb_table *table;
+    struct shash_node *node;
+
+    if (txn_row->old) {
+        /* Mark rows that have weak references to 'txn_row' as modified, so
+         * that their weak references will get reassessed. */
+        struct ovsdb_weak_ref *weak, *next;
+
+        LIST_FOR_EACH_SAFE (weak, next, struct ovsdb_weak_ref, dst_node,
+                            &txn_row->old->dst_refs) {
+            if (!weak->src->txn_row) {
+                ovsdb_txn_row_modify(txn, weak->src);
+            }
+        }
+    }
 
-            SHASH_FOR_EACH (node, &table->schema->columns) {
-                const struct ovsdb_column *column = node->data;
+    if (!txn_row->new) {
+        /* We don't have to do anything about references that originate at
+         * 'txn_row', because ovsdb_row_destroy() will remove those weak
+         * references. */
+        return NULL;
+    }
 
-                if (r->old) {
-                    ovsdb_txn_adjust_row_refs(r->old, column, -delta, NULL);
+    table = txn_row->new->table;
+    SHASH_FOR_EACH (node, &table->schema->columns) {
+        const struct ovsdb_column *column = node->data;
+        struct ovsdb_datum *datum = &txn_row->new->fields[column->index];
+        unsigned int orig_n, i;
+        bool zero = false;
+
+        orig_n = datum->n;
+
+        if (ovsdb_base_type_is_weak_ref(&column->type.key)) {
+            for (i = 0; i < datum->n; ) {
+                const struct ovsdb_row *row;
+
+                row = ovsdb_table_get_row(column->type.key.u.uuid.refTable,
+                                          &datum->keys[i].uuid);
+                if (row) {
+                    add_weak_ref(txn, txn_row->new, row);
+                    i++;
+                } else {
+                    if (uuid_is_zero(&datum->keys[i].uuid)) {
+                        zero = true;
+                    }
+                    ovsdb_datum_remove_unsafe(datum, i, &column->type);
                 }
-                if (r->new) {
-                    ovsdb_txn_adjust_row_refs(r->new, column, delta, &error);
+            }
+        }
+
+        if (ovsdb_base_type_is_weak_ref(&column->type.value)) {
+            for (i = 0; i < datum->n; ) {
+                const struct ovsdb_row *row;
+
+                row = ovsdb_table_get_row(column->type.value.u.uuid.refTable,
+                                          &datum->values[i].uuid);
+                if (row) {
+                    add_weak_ref(txn, txn_row->new, row);
+                    i++;
+                } else {
+                    if (uuid_is_zero(&datum->values[i].uuid)) {
+                        zero = true;
+                    }
+                    ovsdb_datum_remove_unsafe(datum, i, &column->type);
+                }
+            }
+        }
+
+        if (datum->n != orig_n) {
+            bitmap_set1(txn_row->changed, column->index);
+            ovsdb_datum_sort_assert(datum, column->type.key.type);
+            if (datum->n < column->type.n_min) {
+                const struct uuid *row_uuid = ovsdb_row_get_uuid(txn_row->new);
+                if (zero && !txn_row->old) {
+                    return ovsdb_error(
+                        "constraint violation",
+                        "Weak reference column \"%s\" in \"%s\" row "UUID_FMT
+                        " (inserted within this transaction) contained "
+                        "all-zeros UUID (probably as the default value for "
+                        "this column) but deleting this value caused a "
+                        "constraint volation because this column is not "
+                        "allowed to be empty.", column->name,
+                        table->schema->name, UUID_ARGS(row_uuid));
+                } else {
+                    return ovsdb_error(
+                        "constraint violation",
+                        "Deletion of %u weak reference(s) to deleted (or "
+                        "never-existing) rows from column \"%s\" in \"%s\" "
+                        "row "UUID_FMT" %scaused this column to become empty, "
+                        "but constraints on this column disallow an "
+                        "empty column.",
+                        orig_n - datum->n, column->name, table->schema->name,
+                        UUID_ARGS(row_uuid),
+                        (txn_row->old
+                         ? ""
+                         : "(inserted within this transaction) "));
                 }
             }
         }
     }
-    return error;
-}
 
-static void
-ovsdb_txn_rollback_counts(struct ovsdb_txn *txn)
-{
-    ovsdb_error_destroy(ovsdb_txn_adjust_ref_counts__(txn, -1));
+    return NULL;
 }
 
 static struct ovsdb_error * WARN_UNUSED_RESULT
-ovsdb_txn_commit_ref_counts(struct ovsdb_txn *txn)
+determine_changes(struct ovsdb_txn *txn, struct ovsdb_txn_row *txn_row)
 {
-    struct ovsdb_error *error = ovsdb_txn_adjust_ref_counts__(txn, 1);
-    if (error) {
-        ovsdb_txn_rollback_counts(txn);
+    struct ovsdb_table *table;
+
+    table = (txn_row->old ? txn_row->old : txn_row->new)->table;
+    if (txn_row->old && txn_row->new) {
+        struct shash_node *node;
+        bool changed = false;
+
+        SHASH_FOR_EACH (node, &table->schema->columns) {
+            const struct ovsdb_column *column = node->data;
+            const struct ovsdb_type *type = &column->type;
+            unsigned int idx = column->index;
+
+            if (!ovsdb_datum_equals(&txn_row->old->fields[idx],
+                                    &txn_row->new->fields[idx],
+                                    type)) {
+                bitmap_set1(txn_row->changed, idx);
+                changed = true;
+            }
+        }
+
+        if (!changed) {
+            /* Nothing actually changed in this row, so drop it. */
+            ovsdb_txn_row_abort(txn, txn_row);
+        }
+    } else {
+        bitmap_set_multiple(txn_row->changed, 0,
+                            shash_count(&table->schema->columns), 1);
     }
-    return error;
+
+    return NULL;
 }
 
 static struct ovsdb_error * WARN_UNUSED_RESULT
-update_ref_counts(struct ovsdb_txn *txn)
+check_max_rows(struct ovsdb_txn *txn)
 {
-    struct ovsdb_error *error;
     struct ovsdb_txn_table *t;
 
-    error = ovsdb_txn_commit_ref_counts(txn);
-    if (error) {
-        return error;
-    }
-
     LIST_FOR_EACH (t, struct ovsdb_txn_table, node, &txn->txn_tables) {
-        struct ovsdb_txn_row *r;
-
-        HMAP_FOR_EACH (r, struct ovsdb_txn_row, hmap_node, &t->txn_rows) {
-            if (!r->new && r->old->n_refs) {
-                error = ovsdb_error("referential integrity violation",
-                                    "cannot delete %s row "UUID_FMT" because "
-                                    "of %zu remaining reference(s)",
-                                    t->table->schema->name,
-                                    UUID_ARGS(ovsdb_row_get_uuid(r->old)),
-                                    r->old->n_refs);
-                ovsdb_txn_rollback_counts(txn);
-                return error;
-            }
+        size_t n_rows = hmap_count(&t->table->rows);
+        unsigned int max_rows = t->table->schema->max_rows;
+
+        if (n_rows > max_rows) {
+            return ovsdb_error("constraint violation",
+                               "transaction causes \"%s\" table to contain "
+                               "%zu rows, greater than the schema-defined "
+                               "limit of %u row(s)",
+                               t->table->schema->name, n_rows, max_rows);
         }
     }
 
@@ -288,12 +473,41 @@ ovsdb_txn_commit(struct ovsdb_txn *txn, bool durable)
     struct ovsdb_replica *replica;
     struct ovsdb_error *error;
 
+    /* Figure out what actually changed, and abort early if the transaction
+     * was really a no-op. */
+    error = for_each_txn_row(txn, determine_changes);
+    if (error) {
+        ovsdb_error_destroy(error);
+        return OVSDB_BUG("can't happen");
+    }
+    if (list_is_empty(&txn->txn_tables)) {
+        ovsdb_txn_abort(txn);
+        return NULL;
+    }
+
+    /* Check maximum rows table constraints. */
+    error = check_max_rows(txn);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Update reference counts and check referential integrity. */
     error = update_ref_counts(txn);
     if (error) {
         ovsdb_txn_abort(txn);
         return error;
     }
 
+    /* Check reference counts and remove bad reference for "weak" referential
+     * integrity. */
+    error = for_each_txn_row(txn, assess_weak_refs);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Send the commit to each replica. */
     LIST_FOR_EACH (replica, struct ovsdb_replica, node, &txn->db->replicas) {
         error = (replica->class->commit)(replica, txn, durable);
         if (error) {
@@ -306,8 +520,11 @@ ovsdb_txn_commit(struct ovsdb_txn *txn, bool durable)
         }
     }
 
+    /* Finalize commit. */
     txn->db->run_triggers = true;
-    ovsdb_txn_destroy(txn, ovsdb_txn_row_commit);
+    ovsdb_error_assert(for_each_txn_row(txn, ovsdb_txn_row_commit));
+    ovsdb_txn_free(txn);
+
     return NULL;
 }
 
@@ -320,7 +537,7 @@ ovsdb_txn_for_each_change(const struct ovsdb_txn *txn,
 
     LIST_FOR_EACH (t, struct ovsdb_txn_table, node, &txn->txn_tables) {
         HMAP_FOR_EACH (r, struct ovsdb_txn_row, hmap_node, &t->txn_rows) {
-            if (!cb(r->old, r->new, aux)) {
+            if (!cb(r->old, r->new, r->changed, aux)) {
                 break;
             }
         }
@@ -336,6 +553,7 @@ ovsdb_txn_create_txn_table(struct ovsdb_txn *txn, struct ovsdb_table *table)
         table->txn_table = txn_table = xmalloc(sizeof *table->txn_table);
         txn_table->table = table;
         hmap_init(&txn_table->txn_rows);
+        txn_table->serial = serial - 1;
         list_push_back(&txn->txn_tables, &txn_table->node);
     }
     return table->txn_table;
@@ -343,14 +561,26 @@ ovsdb_txn_create_txn_table(struct ovsdb_txn *txn, struct ovsdb_table *table)
 
 static struct ovsdb_txn_row *
 ovsdb_txn_row_create(struct ovsdb_txn *txn, struct ovsdb_table *table,
-                     const struct ovsdb_row *old, struct ovsdb_row *new)
+                     const struct ovsdb_row *old_, struct ovsdb_row *new)
 {
+    struct ovsdb_row *old = (struct ovsdb_row *) old_;
+    size_t n_columns = shash_count(&table->schema->columns);
     struct ovsdb_txn_table *txn_table;
     struct ovsdb_txn_row *txn_row;
 
-    txn_row = xmalloc(sizeof *txn_row);
+    txn_row = xzalloc(offsetof(struct ovsdb_txn_row, changed)
+                      + bitmap_n_bytes(n_columns));
     txn_row->old = (struct ovsdb_row *) old;
     txn_row->new = new;
+    txn_row->n_refs = old ? old->n_refs : 0;
+    txn_row->serial = serial - 1;
+
+    if (old) {
+        old->txn_row = txn_row;
+    }
+    if (new) {
+        new->txn_row = txn_row;
+    }
 
     txn_table = ovsdb_txn_create_txn_table(txn, table);
     hmap_insert(&txn_table->txn_rows, &txn_row->hmap_node,
@@ -374,7 +604,7 @@ ovsdb_txn_row_modify(struct ovsdb_txn *txn, const struct ovsdb_row *ro_row_)
         rw_row = ovsdb_row_clone(ro_row);
         rw_row->n_refs = ro_row->n_refs;
         uuid_generate(ovsdb_row_get_version_rw(rw_row));
-        rw_row->txn_row = ovsdb_txn_row_create(txn, table, ro_row, rw_row);
+        ovsdb_txn_row_create(txn, table, ro_row, rw_row);
         hmap_replace(&table->rows, &ro_row->hmap_node, &rw_row->hmap_node);
 
         return rw_row;
@@ -389,7 +619,7 @@ ovsdb_txn_row_insert(struct ovsdb_txn *txn, struct ovsdb_row *row)
 
     uuid_generate(ovsdb_row_get_version_rw(row));
 
-    row->txn_row = ovsdb_txn_row_create(txn, table, NULL, row);
+    ovsdb_txn_row_create(txn, table, NULL, row);
     hmap_insert(&table->rows, &row->hmap_node, hash);
 }
 
@@ -405,7 +635,7 @@ ovsdb_txn_row_delete(struct ovsdb_txn *txn, const struct ovsdb_row *row_)
     hmap_remove(&table->rows, &row->hmap_node);
 
     if (!txn_row) {
-        row->txn_row = ovsdb_txn_row_create(txn, table, row, NULL);
+        ovsdb_txn_row_create(txn, table, row, NULL);
     } else {
         assert(txn_row->new == row);
         if (txn_row->old) {
@@ -432,3 +662,91 @@ ovsdb_txn_get_comment(const struct ovsdb_txn *txn)
 {
     return txn->comment.length ? ds_cstr_ro(&txn->comment) : NULL;
 }
+
+static void
+ovsdb_txn_row_prefree(struct ovsdb_txn_row *txn_row)
+{
+    struct ovsdb_row *row = txn_row->old ? txn_row->old : txn_row->new;
+    struct ovsdb_txn_table *txn_table = row->table->txn_table;
+
+    txn_table->n_processed--;
+    hmap_remove(&txn_table->txn_rows, &txn_row->hmap_node);
+
+    if (txn_row->old) {
+        txn_row->old->txn_row = NULL;
+    }
+    if (txn_row->new) {
+        txn_row->new->txn_row = NULL;
+    }
+}
+
+static void
+ovsdb_txn_table_destroy(struct ovsdb_txn_table *txn_table)
+{
+    assert(hmap_is_empty(&txn_table->txn_rows));
+    txn_table->table->txn_table = NULL;
+    hmap_destroy(&txn_table->txn_rows);
+    list_remove(&txn_table->node);
+    free(txn_table);
+}
+
+/* Calls 'cb' for every txn_row within 'txn'.  If 'cb' returns nonnull, this
+ * aborts the iteration and for_each_txn_row() passes the error up.  Otherwise,
+ * returns a null pointer after iteration is complete.
+ *
+ * 'cb' may insert new txn_rows and new txn_tables into 'txn'.  It may delete
+ * the txn_row that it is passed in, or txn_rows in txn_tables other than the
+ * one passed to 'cb'.  It may *not* delete txn_rows other than the one passed
+ * in within the same txn_table.  It may *not* delete any txn_tables.  As long
+ * as these rules are followed, 'cb' will be called exactly once for each
+ * txn_row in 'txn', even those added by 'cb'.
+ */
+static struct ovsdb_error * WARN_UNUSED_RESULT
+for_each_txn_row(struct ovsdb_txn *txn,
+                 struct ovsdb_error *(*cb)(struct ovsdb_txn *,
+                                           struct ovsdb_txn_row *))
+{
+    bool any_work;
+
+    serial++;
+
+    do {
+        struct ovsdb_txn_table *t, *next_txn_table;
+
+        any_work = false;
+        LIST_FOR_EACH_SAFE (t, next_txn_table, struct ovsdb_txn_table, node,
+                            &txn->txn_tables) {
+            if (t->serial != serial) {
+                t->serial = serial;
+                t->n_processed = 0;
+            }
+
+            while (t->n_processed < hmap_count(&t->txn_rows)) {
+                struct ovsdb_txn_row *r, *next_txn_row;
+
+                HMAP_FOR_EACH_SAFE (r, next_txn_row,
+                                    struct ovsdb_txn_row, hmap_node,
+                                    &t->txn_rows) {
+                    if (r->serial != serial) {
+                        struct ovsdb_error *error;
+
+                        r->serial = serial;
+                        t->n_processed++;
+                        any_work = true;
+
+                        error = cb(txn, r);
+                        if (error) {
+                            return error;
+                        }
+                    }
+                }
+            }
+            if (hmap_is_empty(&t->txn_rows)) {
+                /* Table is empty.  Drop it. */
+                ovsdb_txn_table_destroy(t);
+            }
+        }
+    } while (any_work);
+
+    return NULL;
+}