Remember oldest reader txnid

Don't walk the readers table unless we really need to.

diff --git a/libraries/liblmdb/mdb.c b/libraries/liblmdb/mdb.c
index 540b55dd04a941de2605ca68a965f162b07da200..1e784ae11de1b8ad549037fd2b11aceed37a7cef 100644 (file)
--- a/libraries/liblmdb/mdb.c
+++ b/libraries/liblmdb/mdb.c
@@ -1083,6 +1083,7 @@ typedef struct MDB_xcursor {
 typedef struct MDB_pgstate {
        pgno_t          *mf_pghead;     /**< Reclaimed freeDB pages, or NULL before use */
        txnid_t         mf_pglast;      /**< ID of last used record, or 0 if !mf_pghead */
+       txnid_t         mf_pgoldest;    /**< ID of oldest reader last time we looked */
 } MDB_pgstate;
 
        /** The database environment. */
@@ -1121,6 +1122,7 @@ struct MDB_env {
        MDB_pgstate     me_pgstate;             /**< state of old pages from freeDB */
 #      define          me_pglast       me_pgstate.mf_pglast
 #      define          me_pghead       me_pgstate.mf_pghead
+#      define          me_pgoldest     me_pgstate.mf_pgoldest
        MDB_page        *me_dpages;             /**< list of malloc'd blocks for re-use */
        /** IDL of pages that became unused in a write txn */
        MDB_IDL         me_free_pgs;
@@ -1956,6 +1958,7 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
        txnid_t oldest = 0, last;
        MDB_cursor_op op;
        MDB_cursor m2;
+       int found_old = 0;
 
        /* If there are any loose pages, just use them */
        if (num == 1 && txn->mt_loose_pgs) {
@@ -1997,8 +2000,8 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 
                if (op == MDB_FIRST) {  /* 1st iteration */
                        /* Prepare to fetch more and coalesce */
-                       oldest = mdb_find_oldest(txn);
                        last = env->me_pglast;
+                       oldest = env->me_pgoldest;
                        mdb_cursor_init(&m2, txn, FREE_DBI, NULL);
                        if (last) {
                                op = MDB_SET_RANGE;
@@ -2013,8 +2016,15 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
 
                last++;
                /* Do not fetch more if the record will be too recent */
-               if (oldest <= last)
-                       break;
+               if (oldest <= last) {
+                       if (!found_old) {
+                               oldest = mdb_find_oldest(txn);
+                               env->me_pgoldest = oldest;
+                               found_old = 1;
+                       }
+                       if (oldest <= last)
+                               break;
+               }
                rc = mdb_cursor_get(&m2, &key, NULL, op);
                if (rc) {
                        if (rc == MDB_NOTFOUND)
@@ -2022,8 +2032,15 @@ mdb_page_alloc(MDB_cursor *mc, int num, MDB_page **mp)
                        goto fail;
                }
                last = *(txnid_t*)key.mv_data;
-               if (oldest <= last)
-                       break;
+               if (oldest <= last) {
+                       if (!found_old) {
+                               oldest = mdb_find_oldest(txn);
+                               env->me_pgoldest = oldest;
+                               found_old = 1;
+                       }
+                       if (oldest <= last)
+                               break;
+               }
                np = m2.mc_pg[m2.mc_top];
                leaf = NODEPTR(np, m2.mc_ki[m2.mc_top]);
                if ((rc = mdb_node_read(txn, leaf, &data)) != MDB_SUCCESS)