X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=ovsdb%2Ftransaction.c;h=be40df9a853e2089c2ccc863b0ecbcc99f2f24e8;hb=HEAD;hp=45b208394267875d050b1abbcf3ecc8422b62c5a;hpb=d171b5846f4988e66c45a6ed5998bbaef82571f9;p=sliver-openvswitch.git

diff --git a/ovsdb/transaction.c b/ovsdb/transaction.c
index 45b208394..be40df9a8 100644
--- a/ovsdb/transaction.c
+++ b/ovsdb/transaction.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2009 Nicira Networks
+/* Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,12 +17,12 @@
 
 #include "transaction.h"
 
-#include <assert.h>
-
+#include "bitmap.h"
 #include "dynamic-string.h"
 #include "hash.h"
 #include "hmap.h"
 #include "json.h"
+#include "list.h"
 #include "ovsdb-error.h"
 #include "ovsdb.h"
 #include "row.h"
@@ -31,15 +31,24 @@
 
 struct ovsdb_txn {
     struct ovsdb *db;
-    struct hmap txn_tables;     /* Contains "struct ovsdb_txn_table"s. */
+    struct list txn_tables;     /* Contains "struct ovsdb_txn_table"s. */
     struct ds comment;
 };
 
 /* A table modified by a transaction. */
 struct ovsdb_txn_table {
-    struct hmap_node hmap_node; /* Element in ovsdb_txn's txn_tables hmap. */
+    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. */
+
+    /* This has the same form as the 'indexes' member of struct ovsdb_table,
+     * but it is only used or updated at transaction commit time, from
+     * check_index_uniqueness(). */
+    struct hmap *txn_indexes;
+
+    /* 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:
@@ -51,84 +60,691 @@ struct ovsdb_txn_table {
  *
  *      - A row modified by a transaction will have non-null 'old' and 'new'.
  *
- *      - 'old' and 'new' both null is invalid.  It would indicate that a row
- *        was added then deleted within a single transaction, but we instead
- *        handle that case by deleting the txn_row entirely.
+ *      - 'old' and 'new' both null indicates that a row was added then deleted
+ *        within a single transaction.  Most of the time we instead delete the
+ *        ovsdb_txn_row entirely, but inside a for_each_txn_row() callback
+ *        there are restrictions that sometimes mean we have to leave the
+ *        ovsdb_txn_row in place.
  */
 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. */
+
+    /* These members are the same as the corresponding members of 'old' or
+     * 'new'.  They are present here for convenience and because occasionally
+     * there can be an ovsdb_txn_row where both 'old' and 'new' are NULL. */
+    struct uuid uuid;
+    struct ovsdb_table *table;
+
+    /* 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 struct ovsdb_error * WARN_UNUSED_RESULT
+delete_garbage_row(struct ovsdb_txn *txn, struct ovsdb_txn_row *r);
+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)
 {
     struct ovsdb_txn *txn = xmalloc(sizeof *txn);
     txn->db = db;
-    hmap_init(&txn->txn_tables);
+    list_init(&txn->txn_tables);
     ds_init(&txn->comment);
     return txn;
 }
 
 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;
-
-    HMAP_FOR_EACH_SAFE (txn_table, next_txn_table,
-                        struct ovsdb_txn_table, hmap_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);
-        }
-
-        hmap_destroy(&txn_table->txn_rows);
-        free(txn_table);
-    }
-    hmap_destroy(&txn->txn_tables);
+    ovs_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);
+        if (new) {
+            hmap_remove(&new->table->rows, &new->hmap_node);
+        }
     } else if (!new) {
         hmap_insert(&old->table->rows, &old->hmap_node, ovsdb_row_hash(old));
     } else {
         hmap_replace(&new->table->rows, &new->hmap_node, &old->hmap_node);
     }
     ovsdb_row_destroy(new);
+    free(txn_row);
+
+    return NULL;
+}
+
+/* Returns the offset in bytes from the start of an ovsdb_row for 'table' to
+ * the hmap_node for the index numbered 'i'. */
+static size_t
+ovsdb_row_index_offset__(const struct ovsdb_table *table, size_t i)
+{
+    size_t n_fields = shash_count(&table->schema->columns);
+    return (offsetof(struct ovsdb_row, fields)
+            + n_fields * sizeof(struct ovsdb_datum)
+            + i * sizeof(struct hmap_node));
+}
+
+/* Returns the hmap_node in 'row' for the index numbered 'i'. */
+static struct hmap_node *
+ovsdb_row_get_index_node(struct ovsdb_row *row, size_t i)
+{
+    return (void *) ((char *) row + ovsdb_row_index_offset__(row->table, i));
+}
+
+/* Returns the ovsdb_row given 'index_node', which is a pointer to that row's
+ * hmap_node for the index numbered 'i' within 'table'. */
+static struct ovsdb_row *
+ovsdb_row_from_index_node(struct hmap_node *index_node,
+                          const struct ovsdb_table *table, size_t i)
+{
+    return (void *) ((char *) index_node - ovsdb_row_index_offset__(table, i));
 }
 
 void
 ovsdb_txn_abort(struct ovsdb_txn *txn)
 {
-    ovsdb_txn_destroy(txn, ovsdb_txn_row_abort);
+    ovsdb_error_assert(for_each_txn_row(txn, ovsdb_txn_row_abort));
+    ovsdb_txn_free(txn);
 }
 
-static void
-ovsdb_txn_row_commit(struct ovsdb_txn_row *txn_row)
+static struct ovsdb_txn_row *
+find_txn_row(const struct ovsdb_table *table, const struct uuid *uuid)
+{
+    struct ovsdb_txn_row *txn_row;
+
+    if (!table->txn_table) {
+        return NULL;
+    }
+
+    HMAP_FOR_EACH_WITH_HASH (txn_row, hmap_node,
+                             uuid_hash(uuid), &table->txn_table->txn_rows) {
+        if (uuid_equals(uuid, &txn_row->uuid)) {
+            return txn_row;
+        }
+    }
+
+    return NULL;
+}
+
+static struct ovsdb_txn_row *
+find_or_make_txn_row(struct ovsdb_txn *txn, const struct ovsdb_table *table,
+                     const struct uuid *uuid)
+{
+    struct ovsdb_txn_row *txn_row = find_txn_row(table, 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;
+        }
+    }
+    return txn_row;
+}
+
+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;
+
+        if (uuid_equals(uuid, ovsdb_row_get_uuid(r))) {
+            /* Self-references don't count. */
+            continue;
+        }
+
+        txn_row = find_or_make_txn_row(txn, table, uuid);
+        if (!txn_row) {
+            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 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];
+    struct ovsdb_error *error;
+
+    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);
+    }
+    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->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) {
+                return OVSDB_WRAP_BUG("error decreasing refcount", error);
+            }
+        }
+        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
+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 %"PRIuSIZE" remaining reference(s)",
+                           r->table->schema->name, UUID_ARGS(&r->uuid),
+                           r->n_refs);
+    }
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+delete_row_refs(struct ovsdb_txn *txn, const struct ovsdb_row *row,
+                const struct ovsdb_base_type *base,
+                const union ovsdb_atom *atoms, unsigned int n)
+{
+    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;
+
+        if (uuid_equals(uuid, ovsdb_row_get_uuid(row))) {
+            /* Self-references don't count. */
+            continue;
+        }
+
+        txn_row = find_or_make_txn_row(txn, table, uuid);
+        if (!txn_row) {
+            return OVSDB_BUG("strong ref target missing");
+        } else if (!txn_row->n_refs) {
+            return OVSDB_BUG("strong ref target has zero n_refs");
+        } else if (!txn_row->new) {
+            return OVSDB_BUG("deleted strong ref target");
+        }
+
+        if (--txn_row->n_refs == 0) {
+            struct ovsdb_error *error = delete_garbage_row(txn, txn_row);
+            if (error) {
+                return error;
+            }
+        }
+    }
+
+    return NULL;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+delete_garbage_row(struct ovsdb_txn *txn, struct ovsdb_txn_row *txn_row)
+{
+    struct shash_node *node;
+    struct ovsdb_row *row;
+
+    if (txn_row->table->schema->is_root) {
+        return NULL;
+    }
+
+    row = txn_row->new;
+    txn_row->new = NULL;
+    hmap_remove(&txn_row->table->rows, &row->hmap_node);
+    SHASH_FOR_EACH (node, &txn_row->table->schema->columns) {
+        const struct ovsdb_column *column = node->data;
+        const struct ovsdb_datum *field = &row->fields[column->index];
+        struct ovsdb_error *error;
+
+        error = delete_row_refs(txn, row,
+                                &column->type.key, field->keys, field->n);
+        if (error) {
+            return error;
+        }
+
+        error = delete_row_refs(txn, row,
+                                &column->type.value, field->values, field->n);
+        if (error) {
+            return error;
+        }
+    }
+    ovsdb_row_destroy(row);
+
+    return NULL;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+collect_garbage(struct ovsdb_txn *txn, struct ovsdb_txn_row *txn_row)
 {
+    if (txn_row->new && !txn_row->n_refs) {
+        return delete_garbage_row(txn, txn_row);
+    }
+    return NULL;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+update_ref_counts(struct ovsdb_txn *txn)
+{
+    struct ovsdb_error *error;
+
+    error = for_each_txn_row(txn, update_row_ref_count);
+    if (error) {
+        return error;
+    }
+
+    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)
+{
+    size_t n_indexes = txn_row->table->schema->n_indexes;
+
+    if (txn_row->old) {
+        size_t i;
+
+        for (i = 0; i < n_indexes; i++) {
+            struct hmap_node *node = ovsdb_row_get_index_node(txn_row->old, i);
+            hmap_remove(&txn_row->table->indexes[i], node);
+        }
+    }
+    if (txn_row->new) {
+        size_t i;
+
+        for (i = 0; i < n_indexes; i++) {
+            struct hmap_node *node = ovsdb_row_get_index_node(txn_row->new, i);
+            hmap_insert(&txn_row->table->indexes[i], node, node->hash);
+        }
+    }
+
+    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 = CONST_CAST(struct ovsdb_row *, src_);
+    struct ovsdb_row *dst = CONST_CAST(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, dst_node, &txn_row->old->dst_refs) {
+            if (!weak->src->txn_row) {
+                ovsdb_txn_row_modify(txn, weak->src);
+            }
+        }
+    }
+
+    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;
+    }
+
+    table = txn_row->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 (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, OVSDB_COL_VERSION);
+            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 NULL;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+determine_changes(struct ovsdb_txn *txn, struct ovsdb_txn_row *txn_row)
+{
+    struct ovsdb_table *table = txn_row->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 NULL;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+check_max_rows(struct ovsdb_txn *txn)
+{
+    struct ovsdb_txn_table *t;
+
+    LIST_FOR_EACH (t, node, &txn->txn_tables) {
+        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 "
+                               "%"PRIuSIZE" rows, greater than the schema-defined "
+                               "limit of %u row(s)",
+                               t->table->schema->name, n_rows, max_rows);
+        }
+    }
+
+    return NULL;
+}
+
+static struct ovsdb_row *
+ovsdb_index_search(struct hmap *index, struct ovsdb_row *row, size_t i,
+                   uint32_t hash)
+{
+    const struct ovsdb_table *table = row->table;
+    const struct ovsdb_column_set *columns = &table->schema->indexes[i];
+    struct hmap_node *node;
+
+    for (node = hmap_first_with_hash(index, hash); node;
+         node = hmap_next_with_hash(node)) {
+        struct ovsdb_row *irow = ovsdb_row_from_index_node(node, table, i);
+        if (ovsdb_row_equal_columns(row, irow, columns)) {
+            return irow;
+        }
+    }
+
+    return NULL;
+}
+
+static void
+duplicate_index_row__(const struct ovsdb_column_set *index,
+                      const struct ovsdb_row *row,
+                      const char *title,
+                      struct ds *out)
+{
+    size_t n_columns = shash_count(&row->table->schema->columns);
+
+    ds_put_format(out, "%s row, with UUID "UUID_FMT", ",
+                  title, UUID_ARGS(ovsdb_row_get_uuid(row)));
+    if (!row->txn_row
+        || bitmap_scan(row->txn_row->changed, 1, 0, n_columns) == n_columns) {
+        ds_put_cstr(out, "existed in the database before this "
+                    "transaction and was not modified by the transaction.");
+    } else if (!row->txn_row->old) {
+        ds_put_cstr(out, "was inserted by this transaction.");
+    } else if (ovsdb_row_equal_columns(row->txn_row->old,
+                                       row->txn_row->new, index)) {
+        ds_put_cstr(out, "existed in the database before this "
+                    "transaction, which modified some of the row's columns "
+                    "but not any columns in this index.");
+    } else {
+        ds_put_cstr(out, "had the following index values before the "
+                    "transaction: ");
+        ovsdb_row_columns_to_string(row->txn_row->old, index, out);
+        ds_put_char(out, '.');
+    }
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+duplicate_index_row(const struct ovsdb_column_set *index,
+                    const struct ovsdb_row *a,
+                    const struct ovsdb_row *b)
+{
+    struct ovsdb_column_set all_columns;
+    struct ovsdb_error *error;
+    char *index_s;
+    struct ds s;
+
+    /* Put 'a' and 'b' in a predictable order to make error messages
+     * reproducible for testing. */
+    ovsdb_column_set_init(&all_columns);
+    ovsdb_column_set_add_all(&all_columns, a->table);
+    if (ovsdb_row_compare_columns_3way(a, b, &all_columns) < 0) {
+        const struct ovsdb_row *tmp = a;
+        a = b;
+        b = tmp;
+    }
+    ovsdb_column_set_destroy(&all_columns);
+
+    index_s = ovsdb_column_set_to_string(index);
+
+    ds_init(&s);
+    ds_put_format(&s, "Transaction causes multiple rows in \"%s\" table to "
+                  "have identical values (", a->table->schema->name);
+    ovsdb_row_columns_to_string(a, index, &s);
+    ds_put_format(&s, ") for index on %s.  ", index_s);
+    duplicate_index_row__(index, a, "First", &s);
+    ds_put_cstr(&s, "  ");
+    duplicate_index_row__(index, b, "Second", &s);
+
+    free(index_s);
+
+    error = ovsdb_error("constraint violation", "%s", ds_cstr(&s));
+    ds_destroy(&s);
+    return error;
+}
+
+static struct ovsdb_error * WARN_UNUSED_RESULT
+check_index_uniqueness(struct ovsdb_txn *txn OVS_UNUSED,
+                       struct ovsdb_txn_row *txn_row)
+{
+    struct ovsdb_txn_table *txn_table = txn_row->table->txn_table;
+    struct ovsdb_table *table = txn_row->table;
+    struct ovsdb_row *row = txn_row->new;
+    size_t i;
+
+    if (!row) {
+        return NULL;
+    }
+
+    for (i = 0; i < table->schema->n_indexes; i++) {
+        const struct ovsdb_column_set *index = &table->schema->indexes[i];
+        struct ovsdb_row *irow;
+        uint32_t hash;
+
+        hash = ovsdb_row_hash_columns(row, index, 0);
+        irow = ovsdb_index_search(&txn_table->txn_indexes[i], row, i, hash);
+        if (irow) {
+            return duplicate_index_row(index, irow, row);
+        }
+
+        irow = ovsdb_index_search(&table->indexes[i], row, i, hash);
+        if (irow && !irow->txn_row) {
+            return duplicate_index_row(index, irow, row);
+        }
+
+        hmap_insert(&txn_table->txn_indexes[i],
+                    ovsdb_row_get_index_node(row, i), hash);
+    }
+
+    return NULL;
 }
 
 struct ovsdb_error *
@@ -137,20 +753,71 @@ ovsdb_txn_commit(struct ovsdb_txn *txn, bool durable)
     struct ovsdb_replica *replica;
     struct ovsdb_error *error;
 
-    LIST_FOR_EACH (replica, struct ovsdb_replica, node, &txn->db->replicas) {
+    /* 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) {
+        return OVSDB_WRAP_BUG("can't happen", error);
+    }
+    if (list_is_empty(&txn->txn_tables)) {
+        ovsdb_txn_abort(txn);
+        return NULL;
+    }
+
+    /* Update reference counts and check referential integrity. */
+    error = update_ref_counts(txn);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Delete unreferenced, non-root rows. */
+    error = for_each_txn_row(txn, collect_garbage);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return OVSDB_WRAP_BUG("can't happen", error);
+    }
+
+    /* Check maximum rows table constraints. */
+    error = check_max_rows(txn);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Check reference counts and remove bad references for "weak" referential
+     * integrity. */
+    error = for_each_txn_row(txn, assess_weak_refs);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Verify that the indexes will still be unique post-transaction. */
+    error = for_each_txn_row(txn, check_index_uniqueness);
+    if (error) {
+        ovsdb_txn_abort(txn);
+        return error;
+    }
+
+    /* Send the commit to each replica. */
+    LIST_FOR_EACH (replica, node, &txn->db->replicas) {
         error = (replica->class->commit)(replica, txn, durable);
         if (error) {
             /* We don't support two-phase commit so only the first replica is
              * allowed to report an error. */
-            assert(&replica->node == txn->db->replicas.next);
+            ovs_assert(&replica->node == txn->db->replicas.next);
 
             ovsdb_txn_abort(txn);
             return error;
         }
     }
 
+    /* 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;
 }
 
@@ -161,9 +828,9 @@ ovsdb_txn_for_each_change(const struct ovsdb_txn *txn,
     struct ovsdb_txn_table *t;
     struct ovsdb_txn_row *r;
 
-    HMAP_FOR_EACH (t, struct ovsdb_txn_table, hmap_node, &txn->txn_tables) {
-        HMAP_FOR_EACH (r, struct ovsdb_txn_row, hmap_node, &t->txn_rows) {
-            if (!cb(r->old, r->new, aux)) {
+    LIST_FOR_EACH (t, node, &txn->txn_tables) {
+        HMAP_FOR_EACH (r, hmap_node, &t->txn_rows) {
+            if ((r->old || r->new) && !cb(r->old, r->new, r->changed, aux)) {
                 break;
             }
         }
@@ -171,56 +838,55 @@ ovsdb_txn_for_each_change(const struct ovsdb_txn *txn,
 }
 
 static struct ovsdb_txn_table *
-ovsdb_txn_get_txn_table__(struct ovsdb_txn *txn,
-                          const struct ovsdb_table *table,
-                          uint32_t hash)
-{
-    struct ovsdb_txn_table *txn_table;
-
-    HMAP_FOR_EACH_IN_BUCKET (txn_table, struct ovsdb_txn_table, hmap_node,
-                             hash, &txn->txn_tables) {
-        if (txn_table->table == table) {
-            return txn_table;
-        }
-    }
-
-    return NULL;
-}
-
-static struct ovsdb_txn_table *
-ovsdb_txn_get_txn_table(struct ovsdb_txn *txn, const struct ovsdb_table *table)
-{
-    return ovsdb_txn_get_txn_table__(txn, table, hash_pointer(table, 0));
-}
-
-static struct ovsdb_txn_table *
-ovsdb_txn_create_txn_table(struct ovsdb_txn *txn,
-                           struct ovsdb_table *table)
+ovsdb_txn_create_txn_table(struct ovsdb_txn *txn, struct ovsdb_table *table)
 {
-    uint32_t hash = hash_pointer(table, 0);
-    struct ovsdb_txn_table *txn_table;
+    if (!table->txn_table) {
+        struct ovsdb_txn_table *txn_table;
+        size_t i;
 
-    txn_table = ovsdb_txn_get_txn_table__(txn, table, hash);
-    if (!txn_table) {
-        txn_table = xmalloc(sizeof *txn_table);
+        table->txn_table = txn_table = xmalloc(sizeof *table->txn_table);
         txn_table->table = table;
         hmap_init(&txn_table->txn_rows);
-        hmap_insert(&txn->txn_tables, &txn_table->hmap_node, hash);
+        txn_table->serial = serial - 1;
+        txn_table->txn_indexes = xmalloc(table->schema->n_indexes
+                                         * sizeof *txn_table->txn_indexes);
+        for (i = 0; i < table->schema->n_indexes; i++) {
+            hmap_init(&txn_table->txn_indexes[i]);
+        }
+        list_push_back(&txn->txn_tables, &txn_table->node);
     }
-    return txn_table;
+    return table->txn_table;
 }
 
 static struct ovsdb_txn_row *
-ovsdb_txn_row_create(struct ovsdb_txn_table *txn_table,
-                     const struct ovsdb_row *old, struct ovsdb_row *new)
+ovsdb_txn_row_create(struct ovsdb_txn *txn, struct ovsdb_table *table,
+                     const struct ovsdb_row *old_, struct ovsdb_row *new)
 {
-    uint32_t hash = ovsdb_row_hash(old ? old : new);
+    const struct ovsdb_row *row = old_ ? old_ : new;
+    struct ovsdb_row *old = CONST_CAST(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->old = (struct ovsdb_row *) old;
+    txn_row = xzalloc(offsetof(struct ovsdb_txn_row, changed)
+                      + bitmap_n_bytes(n_columns));
+    txn_row->uuid = *ovsdb_row_get_uuid(row);
+    txn_row->table = row->table;
+    txn_row->old = old;
     txn_row->new = new;
-    hmap_insert(&txn_table->txn_rows, &txn_row->hmap_node, hash);
+    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,
+                ovsdb_row_hash(old ? old : new));
 
     return txn_row;
 }
@@ -228,20 +894,19 @@ ovsdb_txn_row_create(struct ovsdb_txn_table *txn_table,
 struct ovsdb_row *
 ovsdb_txn_row_modify(struct ovsdb_txn *txn, const struct ovsdb_row *ro_row_)
 {
-    struct ovsdb_row *ro_row = (struct ovsdb_row *) ro_row_;
+    struct ovsdb_row *ro_row = CONST_CAST(struct ovsdb_row *, ro_row_);
 
     if (ro_row->txn_row) {
-        assert(ro_row == ro_row->txn_row->new);
+        ovs_assert(ro_row == ro_row->txn_row->new);
         return ro_row;
     } else {
         struct ovsdb_table *table = ro_row->table;
-        struct ovsdb_txn_table *txn_table;
         struct ovsdb_row *rw_row;
 
-        txn_table = ovsdb_txn_create_txn_table(txn, table);
         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;
@@ -253,12 +918,10 @@ ovsdb_txn_row_insert(struct ovsdb_txn *txn, struct ovsdb_row *row)
 {
     uint32_t hash = ovsdb_row_hash(row);
     struct ovsdb_table *table = row->table;
-    struct ovsdb_txn_table *txn_table;
 
     uuid_generate(ovsdb_row_get_version_rw(row));
 
-    txn_table = ovsdb_txn_create_txn_table(txn, table);
-    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);
 }
 
@@ -267,23 +930,21 @@ ovsdb_txn_row_insert(struct ovsdb_txn *txn, struct ovsdb_row *row)
 void
 ovsdb_txn_row_delete(struct ovsdb_txn *txn, const struct ovsdb_row *row_)
 {
-    struct ovsdb_row *row = (struct ovsdb_row *) row_;
+    struct ovsdb_row *row = CONST_CAST(struct ovsdb_row *, row_);
     struct ovsdb_table *table = row->table;
     struct ovsdb_txn_row *txn_row = row->txn_row;
-    struct ovsdb_txn_table *txn_table;
 
     hmap_remove(&table->rows, &row->hmap_node);
 
     if (!txn_row) {
-        txn_table = ovsdb_txn_create_txn_table(txn, table);
-        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);
+        ovs_assert(txn_row->new == row);
         if (txn_row->old) {
             txn_row->new = NULL;
         } else {
-            txn_table = ovsdb_txn_get_txn_table(txn, table);
-            hmap_remove(&txn_table->txn_rows, &txn_row->hmap_node);
+            hmap_remove(&table->txn_table->txn_rows, &txn_row->hmap_node);
+            free(txn_row);
         }
         ovsdb_row_destroy(row);
     }
@@ -303,3 +964,98 @@ 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_txn_table *txn_table = txn_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)
+{
+    size_t i;
+
+    ovs_assert(hmap_is_empty(&txn_table->txn_rows));
+
+    for (i = 0; i < txn_table->table->schema->n_indexes; i++) {
+        hmap_destroy(&txn_table->txn_indexes[i]);
+    }
+    free(txn_table->txn_indexes);
+
+    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'.
+ *
+ * (Even though 'cb' is not allowed to delete some txn_rows, it can still
+ * delete any actual row by clearing a txn_row's 'new' member.)
+ */
+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, 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, 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;
+}