diff --git a/src/datomish/db.cljc b/src/datomish/db.cljc
index 6608a972..4e1b718f 100644
--- a/src/datomish/db.cljc
+++ b/src/datomish/db.cljc
@@ -88,6 +88,10 @@
     [db eid]
     "Returns the keyword associated with an id, or the key itself if passed.")
 
+  (part-map
+    [db]
+    "Return the partition map of this database, like {:db.part/user {:start 0x100 :idx 0x101}, ...}.")
+
   (in-transaction!
     [db chan-fn]
     "Evaluate the given pair-chan `chan-fn` in an exclusive transaction. If it returns non-nil,
@@ -113,10 +117,9 @@
     [db fragment merge]
     "Apply added schema fragment to the store, using `merge` as a `merge-with` function.")
 
-  (<next-eid
-    [db id-literal]
-    "Return a unique integer for the given id-literal, accounting for the literal's partition.  The
-    returned integer should never be returned again."))
+  (<apply-db-part-map
+    [db part-map]
+    "Apply updated partition map."))
 
 (defn db? [x]
   (and (satisfies? IDB x)
@@ -495,14 +498,17 @@
                    ;; We index on tx, so the following is fast.
                    ["SELECT * FROM transactions WHERE tx = ?" tx])))))))
 
-(defrecord DB [sqlite-connection schema ident-map]
+(defrecord DB [sqlite-connection schema ident-map part-map]
   ;; ident-map maps between keyword idents and integer entids.  The set of idents and entids is
   ;; disjoint, so we represent both directions of the mapping in the same map for simplicity.  Also
   ;; for simplicity, we assume that an entid has at most one associated ident, and vice-versa.  See
   ;; http://docs.datomic.com/identity.html#idents.
+  ;;
+  ;; The partition-map part-map looks like {:db.part/user {:start 0x100 :idx 0x101}, ...}.  It maps
+  ;; between keyword ident part names and integer ranges, where start is the beginning of the
+  ;; range (for future use to help identify which partition entids lie in, and idx is the current
+  ;; maximum entid in the partition.
 
-  ;; TODO: cache parts.  parts looks like {:db.part/db {:start 0 :current 10}}.  It maps between
-  ;; keyword ident part names and integer ranges.
   IDB
   (query-context [db] (context/make-context (datoms-source db)))
 
@@ -518,6 +524,9 @@
       (get (.-ident-map db) eid eid)
       eid))
 
+  (part-map [db]
+    (:part-map db))
+
   (in-transaction! [db chan-fn]
     (s/in-transaction!
       (:sqlite-connection db) chan-fn))
@@ -551,27 +560,27 @@
           <?
           yield-datom))))
 
-  (<next-eid [db tempid]
-    {:pre [(id-literal? tempid)]}
-    {:post [ds/entid?]}
-    (go-pair
-      ;; TODO: keep all of these eid allocations in the transaction report and apply them at the end
-      ;; of the transaction.
-      (let [exec (partial s/execute! (:sqlite-connection db))
-            part (entid db (:part tempid))]
-        (when-not (ds/entid? part) ;; TODO: cache parts materialized view.
-          (raise "Cannot allocate entid for id-literal " tempid " because part " (:part tempid) " is not known"
-                 {:error :db/bad-part
-                  :part (:part tempid)}))
-
-        (p :next-eid-body
-           (<? (exec ["UPDATE parts SET idx = idx + 1 WHERE part = ?" part]))
-        (:eid (first (<? (s/all-rows (:sqlite-connection db) ["SELECT (start + idx) AS eid FROM parts WHERE part = ?" part]))))))))
-
   (<apply-entities [db tx entities]
     {:pre [(db? db) (sequential? entities)]}
     (-<apply-entities db tx entities))
 
+  (<apply-db-part-map [db part-map]
+    (go-pair
+      (let [exec (partial s/execute! (:sqlite-connection db))]
+        (let [pairs (mapcat (fn [[part {:keys [start idx]}]]
+                              (when-not (= idx (get-in db [:part-map part :idx]))
+                                [(sqlite-schema/->SQLite part) idx]))
+                            part-map)]
+          ;; TODO: chunk into 999/2 sections, for safety.
+          (when-not (empty? pairs)
+            (<?
+              (exec
+                (cons (apply str "UPDATE parts SET idx = CASE"
+                             (concat
+                               (repeat (count pairs) " WHEN part = ? THEN ?")
+                               [" ELSE idx END"]))
+                      pairs))))))
+      (assoc db :part-map part-map)))
 
   (<apply-db-ident-assertions [db added-idents merge]
     (go-pair
@@ -612,9 +621,11 @@
 (defn with-ident [db ident entid]
   (update db :ident-map #(assoc % ident entid, entid ident)))
 
-(defn db [sqlite-connection idents schema]
+(defn db [sqlite-connection idents parts schema]
   {:pre [(map? idents)
          (every? keyword? (keys idents))
+         (map? parts)
+         (every? keyword? (keys parts))
          (map? schema)
          (every? keyword? (keys schema))]}
   (let [entid-schema (ds/schema (into {} (map (fn [[k v]] [(k idents) v]) schema))) ;; TODO: fail if ident missing.
@@ -622,9 +633,9 @@
     (map->DB
       {:sqlite-connection sqlite-connection
        :ident-map         ident-map
+       :part-map          parts
        :symbolic-schema   schema
        :schema            entid-schema
-       ;; TODO :parts
        })))
 
 ;; TODO: factor this into the overall design.
diff --git a/src/datomish/db_factory.cljc b/src/datomish/db_factory.cljc
index 2c8b7131..8e875cd5 100644
--- a/src/datomish/db_factory.cljc
+++ b/src/datomish/db_factory.cljc
@@ -34,6 +34,17 @@
                      (s/all-rows sqlite-connection)))]
       (into {} (map (fn [row] [(sqlite-schema/<-SQLite :db.type/keyword (:ident row)) (:entid row)])) rows))))
 
+(defn <parts [sqlite-connection]
+  "Read the parts map materialized view from the given SQLite store.
+  Returns a map (keyword part) -> {:start integer :idx integer}, like {:db.part/user {start: 0x100 idx: 0x101}}."
+
+  (go-pair
+    (let [rows (<? (->>
+                     {:select [:part :start :idx] :from [:parts]}
+                     (s/format)
+                     (s/all-rows sqlite-connection)))]
+      (into {} (map (fn [row] [(sqlite-schema/<-SQLite :db.type/keyword (:part row)) (select-keys row [:start :idx])])) rows))))
+
 (defn <symbolic-schema [sqlite-connection]
   "Read the schema map materialized view from the given SQLite store.
   Returns a map (keyword ident) -> (map (keyword attribute -> keyword value)), like
@@ -72,7 +83,7 @@
     (when-not (= sqlite-schema/current-version (<? (sqlite-schema/<ensure-current-version sqlite-connection)))
       (raise "Could not ensure current SQLite schema version."))
 
-    (let [db            (db/db sqlite-connection bootstrap/idents bootstrap/symbolic-schema)
+    (let [db            (db/db sqlite-connection bootstrap/idents bootstrap/parts bootstrap/symbolic-schema)
           bootstrapped? (<? (db/<bootstrapped? db))]
       (when-not bootstrapped?
         ;; We need to bootstrap the DB.
@@ -84,40 +95,48 @@
                                                (raise "Altering schema attributes is not yet supported, got " new " altering existing schema attribute " old
                                                       {:error :schema/alter-schema :old old :new new})
                                                new))]
-          (do
-            (let [exec (partial s/execute! (:sqlite-connection db))]
-              ;; TODO: allow inserting new parts.
-              ;; TODO: think more carefully about allocating new parts and bitmasking part ranges.
-              (<? (exec
-                    ["INSERT INTO parts VALUES (?, ?, ?)" (db/entid db :db.part/db) 0x0 (inc (apply max (vals bootstrap/idents)))]))
-              (<? (exec
-                    ["INSERT INTO parts VALUES (?, ?, ?)" (db/entid db :db.part/user) 0x10000 0]))
-              (<? (exec
-                    ["INSERT INTO parts VALUES (?, ?, ?)" (db/entid db :db.part/tx) 0x10000000 0])))
-            (-> db
-                ;; We use <with-internal rather than <transact! to apply the bootstrap transaction
-                ;; data but to not follow the regular schema application process.  We can't apply the
-                ;; schema changes, since the applied datoms would conflict with the bootstrapping
-                ;; idents and schema.  (The bootstrapping idents and schema are required to be able to
-                ;; write to the database conveniently; without them, we'd have to manually write
-                ;; datoms to the store.  It's feasible but awkward.)  After bootstrapping, we read
-                ;; back the idents and schema, just like when we re-open.
-                (transact/<with-internal (bootstrap/tx-data) fail-alter-ident fail-alter-attr)
-                (<?)))))
+          (let [exec (partial s/execute! (:sqlite-connection db))
+                part->vector (fn [[part {:keys [start idx]}]]
+                               (println "part->vector" part start idx)
+                               [(sqlite-schema/->SQLite part) start idx])]
+            ;; TODO: allow inserting new parts.
+            ;; TODO: think more carefully about allocating new parts and bitmasking part ranges.
+            ;; TODO: install these using bootstrap assertions.  It's tricky because the part ranges are implicit.
+            ;; TODO: chunk into 999/3 sections, for safety.
+            (<? (exec
+                  (cons (str "INSERT INTO parts VALUES "
+                             (apply str (interpose ", " (repeat (count bootstrap/parts) "(?, ?, ?)"))))
+                        (mapcat part->vector bootstrap/parts)))))
+
+          (-> db
+              ;; We use <with-internal rather than <transact! to apply the bootstrap transaction
+              ;; data but to not follow the regular schema application process.  We can't apply the
+              ;; schema changes, since the applied datoms would conflict with the bootstrapping
+              ;; idents and schema.  (The bootstrapping idents and schema are required to be able to
+              ;; write to the database conveniently; without them, we'd have to manually write
+              ;; datoms to the store.  It's feasible but awkward.)  After bootstrapping, we read
+              ;; back the idents and schema, just like when we re-open.
+              (transact/<with-internal (bootstrap/tx-data) fail-alter-ident fail-alter-attr)
+              (<?))))
 
       ;; We just bootstrapped, or we are returning to an already bootstrapped DB.
       (let [idents          (<? (<idents sqlite-connection))
+            parts           (<? (<parts sqlite-connection))
             symbolic-schema (<? (<symbolic-schema sqlite-connection))]
         (when-not bootstrapped?
-          ;; TODO: parts.
           (when (not (= idents bootstrap/idents))
             (raise "After bootstrapping database, expected new materialized idents and old bootstrapped idents to be identical"
                    {:error :bootstrap/bad-idents,
                     :new   idents :old bootstrap/idents
                     }))
+          (when (not (= (dissoc parts :db.part/tx) (dissoc bootstrap/parts :db.part/tx))) ;; TODO: work around tx allocation.
+            (raise "After bootstrapping database, expected new materialized parts and old bootstrapped parts to be identical (outside of db.part/tx)"
+                   {:error :bootstrap/bad-parts,
+                    :new   (dissoc parts :db.part/tx) :old (dissoc bootstrap/parts :db.part/tx)
+                    }))
           (when (not (= symbolic-schema bootstrap/symbolic-schema))
             (raise "After bootstrapping database, expected new materialized symbolic schema and old bootstrapped symbolic schema to be identical"
                    {:error :bootstrap/bad-symbolic-schema,
                     :new   symbolic-schema :old bootstrap/symbolic-schema
                     })))
-        (db/db sqlite-connection idents symbolic-schema)))))
+        (db/db sqlite-connection idents parts symbolic-schema)))))
diff --git a/src/datomish/sqlite_schema.cljc b/src/datomish/sqlite_schema.cljc
index 546d0f4d..1aee120c 100644
--- a/src/datomish/sqlite_schema.cljc
+++ b/src/datomish/sqlite_schema.cljc
@@ -112,7 +112,7 @@
    ;; TODO: allow arbitrary schema values (true/false) and tag the resulting values.
    "CREATE TABLE schema (ident TEXT NOT NULL, attr TEXT NOT NULL, value TEXT NOT NULL, FOREIGN KEY (ident) REFERENCES idents (ident))"
    "CREATE INDEX idx_schema_unique ON schema (ident, attr, value)"
-   "CREATE TABLE parts (part INTEGER NOT NULL PRIMARY KEY, start INTEGER NOT NULL, idx INTEGER NOT NULL)"
+   "CREATE TABLE parts (part TEXT NOT NULL PRIMARY KEY, start INTEGER NOT NULL, idx INTEGER NOT NULL)"
    ])
 
 (defn <create-current-version
diff --git a/src/datomish/transact.cljc b/src/datomish/transact.cljc
index b2db09d5..4cb17a33 100644
--- a/src/datomish/transact.cljc
+++ b/src/datomish/transact.cljc
@@ -64,6 +64,7 @@
                      entities  ;; The set of entities (like [:db/add e a v tx]) processed.
                      tx-data   ;; The set of datoms applied to the database, like (Datom. e a v tx added).
                      tempids   ;; The map from id-literal -> numeric entid.
+                     part-map  ;; Map {:db.part/user {:start 0x10000 :idx 0x10000}, ...}.
                      added-parts ;; The set of parts added during the transaction via :db.part/db :db.install/part.
                      added-idents ;; The map of idents -> entid added during the transaction, via e :db/ident ident.
                      added-attributes ;; The map of schema attributes (ident -> schema fragment) added during the transaction, via :db.part/db :db.install/attribute.
@@ -72,11 +73,19 @@
 (defn- report? [x]
   (and (instance? TxReport x)))
 
-(defonce -eid (atom (- 0x200 1)))
-
-;; TODO: better here.
-(defn- next-eid [db]
-  (swap! -eid inc))
+(defn- -next-eid! [part-map-atom tempid]
+  "Advance {:db.part/user {:start 0x10 :idx 0x11}, ...} to {:db.part/user {:start 0x10 :idx 0x12}, ...} and return 0x12."
+  {:pre [(id-literal? tempid)]}
+  (let [part (:part tempid)
+        next (fn [part-map]
+               (let [idx (get-in part-map [part :idx])]
+                 (when-not idx
+                   (raise "Cannot allocate entid for id-literal " tempid " because part " part " is not known"
+                          {:error :db/bad-part
+                           :parts (sorted-set (keys part-map))
+                           :part  part}))
+                 (update-in part-map [part :idx] inc)))]
+    (get-in (swap! part-map-atom next) [part :idx])))
 
 (defn- allocate-eid
   [report id-literal eid]
@@ -327,22 +336,22 @@
                   allocated-eid (get-in report [:tempids e])]
               (if (and upserted-eid allocated-eid (not= upserted-eid allocated-eid))
                 (<? (<retry-with-tempid db initial-report initial-entities e upserted-eid)) ;; TODO: not initial report, just the sorted entities here.
-                (let [eid (or upserted-eid allocated-eid (<? (db/<next-eid db e)))]
+                (let [eid (or upserted-eid allocated-eid (-next-eid! (:part-map-atom report) e))]
                   (recur (allocate-eid report e eid) (cons [op eid a v] entities)))))
 
             ;; Start allocating and retrying.  We try with e last, so as to eventually upsert it.
             (id-literal? v)
             ;; We can't fail with unbound literals here, since we could have multiple.
-            (let [eid (or (get-in report [:tempids v]) (<? (db/<next-eid db e)))]
+            (let [eid (or (get-in report [:tempids v]) (-next-eid! (:part-map-atom report) e))]
               (recur (allocate-eid report v eid) (cons [op e a eid] entities)))
 
             (id-literal? a)
             ;; TODO: should we even allow id-literal attributes?  Datomic fails in some cases here.
-            (let [eid (or (get-in report [:tempids a]) (<? (db/<next-eid db e)))]
+            (let [eid (or (get-in report [:tempids a]) (-next-eid! (:part-map-atom report) e))]
               (recur (allocate-eid report a eid) (cons [op e eid v] entities)))
 
             (id-literal? e)
-            (let [eid (or (get-in report [:tempids e]) (<? (db/<next-eid db e)))]
+            (let [eid (or (get-in report [:tempids e]) (-next-eid! (:part-map-atom report) e))]
               (recur (allocate-eid report e eid) (cons [op eid a v] entities)))
 
             true
@@ -453,22 +462,29 @@
 ;; TODO: expose this in a more appropriate way.
 (defn <with-internal [db tx-data merge-ident merge-attr]
   (go-pair
-    (let [report (->>
+    (let [part-map-atom
+          (atom (db/part-map db))
+
+          tx
+          (-next-eid! part-map-atom (id-literal :db.part/tx))
+
+          report (->>
                    (map->TxReport
-                     {:db-before         db
-                      :db-after          db
+                     {:db-before        db
+                      :db-after         db
                       ;; This mimics DataScript.  It's convenient to be able to extract the
                       ;; transaction ID and transaction timestamp directly from the report; Datomic
                       ;; makes this surprisingly difficult: one needs a :db.part/tx temporary and an
                       ;; explicit upsert of that temporary.
-                      :tx                (<? (db/<next-eid db (id-literal :db.part/tx)))
-                      :txInstant         (db/now db)
-                      :entities          tx-data
-                      :tx-data           []
-                      :tempids           {}
-                      :added-parts       {}
-                      :added-idents      {}
-                      :added-attributes  {}
+                      :part-map-atom    part-map-atom
+                      :tx               tx
+                      :txInstant        (db/now db)
+                      :entities         tx-data
+                      :tx-data          []
+                      :tempids          {}
+                      :added-parts      {}
+                      :added-idents     {}
+                      :added-attributes {}
                       })
 
                    (<transact-tx-data db)
@@ -484,6 +500,10 @@
           db-after (->
                      db
 
+                     (db/<apply-db-part-map @(:part-map-atom report))
+                     (<?)
+                     (->> (p :apply-db-part-changes))
+
                      (db/<apply-db-ident-assertions (:added-idents report) merge-ident)
                      (<?)
                      (->> (p :apply-db-ident-assertions))
diff --git a/src/datomish/transact/bootstrap.cljc b/src/datomish/transact/bootstrap.cljc
index 17c90be2..9a7f2e9a 100644
--- a/src/datomish/transact/bootstrap.cljc
+++ b/src/datomish/transact/bootstrap.cljc
@@ -76,9 +76,16 @@
    :db/doc               35
    })
 
+(def parts
+  {:db.part/db   {:start 0 :idx (inc (apply max (vals idents)))}
+   :db.part/user {:start 0x10000 :idx 0x10000}
+   :db.part/tx   {:start 0x10000000 :idx 0x10000000}
+   })
+
 (defn tx-data []
   (concat
     (map (fn [[ident entid]] [:db/add entid :db/ident ident]) idents)
+    ;; TODO: install partitions as well, like (map (fn [[ident entid]] [:db/add :db.part/db :db.install/partition ident])).
     (map (fn [[ident attrs]] (assoc attrs :db/id ident)) symbolic-schema)
     (map (fn [[ident attrs]] [:db/add :db.part/db :db.install/attribute (get idents ident)]) symbolic-schema) ;; TODO: fail if nil.
     ))