mariadb/ft/txn_manager.cc

/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
#ident "$Id$"
#ident "Copyright (c) 2007-2012 Tokutek Inc.  All rights reserved."
#ident "The technology is licensed by the Massachusetts Institute of Technology, Rutgers State University of New Jersey, and the Research Foundation of State University of New York at Stony Brook under United States of America Serial No. 11/760379 and to the patents and/or patent applications resulting from it."


#include "includes.h"
#include "txn.h"
#include "checkpoint.h"
#include "ule.h"
#include <valgrind/helgrind.h>
#include "txn_manager.h"
#include "omt-tmpl.h"
#include "rollback.h"

bool garbage_collection_debug = false;

// internal locking functions, should use this instead of accessing lock directly
static void txn_manager_lock(TXN_MANAGER txn_manager);
static void txn_manager_unlock(TXN_MANAGER txn_manager);

static bool is_txnid_live(TXN_MANAGER txn_manager, TXNID txnid) {
    TOKUTXN result = NULL;
    toku_txn_manager_id2txn_unlocked(txn_manager, txnid, &result);
    return (result != NULL);
}

//Heaviside function to search through an OMT by a TXNID
int find_by_xid (const TOKUTXN &txn, const TXNID &txnidfind);

static void
verify_snapshot_system(TXN_MANAGER txn_manager UU()) {
    uint32_t    num_snapshot_txnids = txn_manager->snapshot_txnids.size();
    TXNID       snapshot_txnids[num_snapshot_txnids];
    uint32_t    num_live_txns = txn_manager->live_txns.size();
    TOKUTXN     live_txns[num_live_txns];
    uint32_t    num_referenced_xid_tuples = txn_manager->referenced_xids.size();
    struct      referenced_xid_tuple  *referenced_xid_tuples[num_referenced_xid_tuples];

    int r;
    uint32_t i;
    uint32_t j;
    //set up arrays for easier access
    for (i = 0; i < num_snapshot_txnids; i++) {
        r = txn_manager->snapshot_txnids.fetch(i, &snapshot_txnids[i]);
        assert_zero(r);
    }
    for (i = 0; i < num_live_txns; i++) {
        r = txn_manager->live_txns.fetch(i, &live_txns[i]);
        assert_zero(r);
    }
    for (i = 0; i < num_referenced_xid_tuples; i++) {
        r = txn_manager->referenced_xids.fetch(i, &referenced_xid_tuples[i]);
        assert_zero(r);
    }

    {
        //Verify snapshot_txnids
        for (i = 0; i < num_snapshot_txnids; i++) {
            TXNID snapshot_xid = snapshot_txnids[i];
            invariant(is_txnid_live(txn_manager, snapshot_xid));
            TOKUTXN snapshot_txn;
            toku_txn_manager_id2txn_unlocked(txn_manager, snapshot_xid, &snapshot_txn);
            uint32_t num_live_root_txn_list = snapshot_txn->live_root_txn_list->size();
            TXNID     live_root_txn_list[num_live_root_txn_list];
            {
                for (j = 0; j < num_live_root_txn_list; j++) {
                    r = snapshot_txn->live_root_txn_list->fetch(j, &live_root_txn_list[j]);
                    assert_zero(r);
                }
            }
            {
                // Only committed entries have return a youngest.
                TXNID youngest = toku_get_youngest_live_list_txnid_for(
                    snapshot_xid,
                    txn_manager->snapshot_txnids,
                    txn_manager->referenced_xids
                    );
                invariant(youngest == TXNID_NONE);
            }
            for (j = 0; j < num_live_root_txn_list; j++) {
                TXNID live_xid = live_root_txn_list[j];
                invariant(live_xid <= snapshot_xid);
                TXNID youngest = toku_get_youngest_live_list_txnid_for(
                    live_xid,
                    txn_manager->snapshot_txnids,
                    txn_manager->referenced_xids
                    );
                if (is_txnid_live(txn_manager, live_xid)) {
                    // Only committed entries have return a youngest.
                    invariant(youngest == TXNID_NONE);
                }
                else {
                    invariant(youngest != TXNID_NONE);
                    // A committed entry might have been read-only, in which case it won't return anything.
                    // This snapshot reads 'live_xid' so it's youngest cannot be older than snapshot_xid.
                    invariant(youngest >= snapshot_xid);
                }
            }
        }
    }
    {
        // Verify referenced_xids.
        for (i = 0; i < num_referenced_xid_tuples; i++) {
            struct referenced_xid_tuple *tuple = referenced_xid_tuples[i];
            invariant(tuple->begin_id < tuple->end_id);
            invariant(tuple->references > 0);

            {
                //verify neither pair->begin_id nor end_id is in live_list
                r = txn_manager->live_txns.find_zero<TXNID, find_by_xid>(tuple->begin_id, nullptr, nullptr);
                invariant(r == DB_NOTFOUND);
                r = txn_manager->live_txns.find_zero<TXNID, find_by_xid>(tuple->end_id, nullptr, nullptr);
                invariant(r == DB_NOTFOUND);
            }
            {
                //verify neither pair->begin_id nor end_id is in snapshot_xids
                r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(tuple->begin_id, nullptr, nullptr);
                invariant(r == DB_NOTFOUND);
                r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(tuple->end_id, nullptr, nullptr);
                invariant(r == DB_NOTFOUND);
            }
            {
                // Verify number of references is correct
                uint32_t refs_found = 0;
                for (j = 0; j < num_snapshot_txnids; j++) {
                    TXNID snapshot_xid = snapshot_txnids[j];
                    TOKUTXN snapshot_txn;
                    toku_txn_manager_id2txn_unlocked(txn_manager, snapshot_xid, &snapshot_txn);

                    if (toku_is_txn_in_live_root_txn_list(*snapshot_txn->live_root_txn_list, tuple->begin_id)) {
                        refs_found++;
                    }
                    invariant(!toku_is_txn_in_live_root_txn_list(
                                *snapshot_txn->live_root_txn_list,
                                tuple->end_id));
                }
                invariant(refs_found == tuple->references);
            }
            {
                // Verify youngest makes sense.
                TXNID youngest = toku_get_youngest_live_list_txnid_for(
                    tuple->begin_id,
                    txn_manager->snapshot_txnids,
                    txn_manager->referenced_xids
                    );
                invariant(youngest != TXNID_NONE);
                invariant(youngest > tuple->begin_id);
                invariant(youngest < tuple->end_id);
                // Youngest must be found, and must be a snapshot txn
                r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(youngest, nullptr, nullptr);
                invariant_zero(r);
            }
        }
    }
    {
        //Verify live_txns
        for (i = 0; i < num_live_txns; i++) {
            TOKUTXN txn = live_txns[i];

            bool expect = txn->snapshot_txnid64 == txn->txnid64;
            {
                //verify pair->xid2 is in snapshot_xids
                r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, nullptr, nullptr);
                invariant(r==0 || r==DB_NOTFOUND);
                invariant((r==0) == (expect!=0));
            }

        }
    }
}

void toku_txn_manager_init(TXN_MANAGER* txn_managerp) {
    TXN_MANAGER XCALLOC(txn_manager);
    toku_mutex_init(&txn_manager->txn_manager_lock, NULL);
    txn_manager->live_txns.create();
    txn_manager->live_root_txns.create();
    txn_manager->snapshot_txnids.create();
    txn_manager->referenced_xids.create();
    txn_manager->last_xid = 0;
    toku_list_init(&txn_manager->prepared_txns);
    toku_list_init(&txn_manager->prepared_and_returned_txns);

    toku_cond_init(&txn_manager->wait_for_unpin_of_txn, 0);
    *txn_managerp = txn_manager;
}

void toku_txn_manager_destroy(TXN_MANAGER txn_manager) {
    toku_mutex_destroy(&txn_manager->txn_manager_lock);
    txn_manager->live_txns.destroy();
    txn_manager->live_root_txns.destroy();
    txn_manager->snapshot_txnids.destroy();
    txn_manager->referenced_xids.destroy();
    toku_cond_destroy(&txn_manager->wait_for_unpin_of_txn);
    toku_free(txn_manager);
}

TXNID
toku_txn_manager_get_oldest_living_xid(TXN_MANAGER txn_manager) {
    TXNID rval = TXNID_NONE_LIVING;
    txn_manager_lock(txn_manager);

    if (txn_manager->live_root_txns.size() > 0) {
        // We use live_root_txns because roots are always older than children,
        // and live_root_txns stores TXNIDs directly instead of TOKUTXNs in live_txns
        int r = txn_manager->live_root_txns.fetch(0, &rval);
        invariant_zero(r);
    }
    txn_manager_unlock(txn_manager);
    return rval;
}

// Create list of root transactions that were live when this txn began.
static void
setup_live_root_txn_list(TXN_MANAGER txn_manager, TOKUTXN txn) {
    invariant(txn_manager->live_root_txns.size() > 0);
    invariant(txn->live_root_txn_list == nullptr);
    XMALLOC(txn->live_root_txn_list);
    txn->live_root_txn_list->clone(txn_manager->live_root_txns);
}

//Heaviside function to search through an OMT by a TXNID
int
find_by_xid (const TOKUTXN &txn, const TXNID &txnidfind) {
    if (txn->txnid64<txnidfind) return -1;
    if (txn->txnid64>txnidfind) return +1;
    return 0;
}

#if 0
static void
omt_insert_at_end_unless_recovery(OMT omt, int (*h)(OMTVALUE, void*extra), TOKUTXN txn, OMTVALUE v, bool for_recovery)
// Effect: insert v into omt that is sorted by xid gotten from txn.
// Rationale:
//   During recovery, we get txns in the order that they did their first
//   write operation, which is not necessarily monotonically increasing.
//   During normal operation, txns are created with strictly increasing
//   txnids, so we can always insert at the end.
{
    int r;
    uint32_t idx = toku_omt_size(omt);
    if (for_recovery) {
        r = toku_omt_find_zero(omt, h, (void *) txn->txnid64, NULL, &idx);
        invariant(r==DB_NOTFOUND);
    }
    r = toku_omt_insert_at(omt, v, idx);
    lazy_assert_zero(r);
}
#endif

static TXNID
max_xid(TXNID a, TXNID b) {
    return a < b ? b : a;
}

int toku_txn_manager_start_txn(
    TOKUTXN *txnp,
    TXN_MANAGER txn_manager,
    TOKUTXN parent,
    TOKULOGGER logger,
    TXNID xid,
    TXN_SNAPSHOT_TYPE snapshot_type,
    DB_TXN *container_db_txn,
    bool for_recovery)
{
    int r;
    XIDS xids;
    TOKUTXN txn;

    // Do as much (safe) work as possible before serializing on the txn_manager lock.
    XIDS parent_xids;
    if (parent == NULL) {
        parent_xids = xids_get_root_xids();
    } else {
        parent_xids = parent->xids;
    }
    r = xids_create_unknown_child(parent_xids, &xids);
    if (r != 0) {
        return r;
    }

    r = toku_txn_create_txn(&txn, parent, logger, snapshot_type, container_db_txn, xids, for_recovery);
    if (r != 0) {
        // logger is panicked
        return r;
    }

    // the act of getting a transaction ID and adding the
    // txn to the proper OMTs must be atomic. MVCC depends
    // on this.
    txn_manager_lock(txn_manager);
    if (garbage_collection_debug) {
        verify_snapshot_system(txn_manager);
    }
    if (xid == TXNID_NONE) {
        invariant(!for_recovery);
        // The transaction manager maintains the latest transaction id.
        xid = ++txn_manager->last_xid;
        invariant(logger);
    }
    else {
        // Recovered transactions may not come in ascending order,
        // because we assign xids when transactions are created but
        // log transactions only when they first perform a write.
        invariant(for_recovery);
        txn_manager->last_xid = max_xid(txn_manager->last_xid, xid);
    }
    xids_finalize_with_child(txn->xids, xid);

    toku_txn_update_xids_in_txn(txn, xid);

    //Add txn to list (omt) of live transactions
    {
        uint32_t idx = txn_manager->live_txns.size();
        if (for_recovery) {
            r = txn_manager->live_txns.find_zero<TXNID, find_by_xid>(txn->txnid64, nullptr, &idx);
            invariant(r==DB_NOTFOUND);
        }
        r = txn_manager->live_txns.insert_at(txn, idx);
        lazy_assert_zero(r);
    }

    {
        //
        // maintain the data structures necessary for MVCC:
        //  1. add txn to list of live_root_txns if this is a root transaction
        //  2. if the transaction is creating a snapshot:
        //    - create a live list for the transaction
        //    - add the id to the list of snapshot ids
        //
        // The order of operations is important here, and must be taken
        // into account when the transaction is closed. The txn is added
        // to the live_root_txns first (if it is a root txn). This has the implication
        // that a root level snapshot transaction is in its own live list. This fact
        // is taken into account when the transaction is closed.

        // add ancestor information, and maintain global live root txn list
        if (parent == NULL) {
            //Add txn to list (omt) of live root txns
            uint32_t idx = txn_manager->live_root_txns.size();
            if (for_recovery) {
                r = txn_manager->live_root_txns.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, nullptr, &idx);
                invariant(r == DB_NOTFOUND);
            }
            r = txn_manager->live_root_txns.insert_at(txn->txnid64, idx);
        }

        // setup information for snapshot reads
        if (txn->snapshot_type != TXN_SNAPSHOT_NONE) {
            // in this case, either this is a root level transaction that needs its live list setup, or it
            // is a child transaction that specifically asked for its own snapshot
            if (parent == NULL || txn->snapshot_type == TXN_SNAPSHOT_CHILD) {
                setup_live_root_txn_list(txn_manager, txn);  

                // Add this txn to the global list of txns that have their own snapshots.
                // (Note, if a txn is a child that creates its own snapshot, then that child xid
                // is the xid stored in the global list.) 
                {
                    uint32_t idx = txn_manager->snapshot_txnids.size();
                    if (for_recovery) {
                        r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, nullptr, &idx);
                        invariant(r == DB_NOTFOUND);
                    }
                    r = txn_manager->snapshot_txnids.insert_at(txn->txnid64, idx);
                    lazy_assert_zero(r);
                }
            }
            // in this case, it is a child transaction that specified its snapshot to be that 
            // of the root transaction
            else if (txn->snapshot_type == TXN_SNAPSHOT_ROOT) {
                txn->live_root_txn_list = parent->live_root_txn_list;
            }
            else {
                assert(false);
            }
        }
    }
    if (garbage_collection_debug) {
        verify_snapshot_system(txn_manager);
    }
    txn_manager_unlock(txn_manager);

    *txnp = txn;
    return 0;
}

// template-only function, but must be extern
int find_tuple_by_xid (const struct referenced_xid_tuple &tuple, const TXNID &xidfind);
int
find_tuple_by_xid (const struct referenced_xid_tuple &tuple, const TXNID &xidfind)
{
    if (tuple.begin_id < xidfind) return -1;
    if (tuple.begin_id > xidfind) return +1;
    return 0;
}

TXNID
toku_get_youngest_live_list_txnid_for(TXNID xc, const xid_omt_t &snapshot_txnids, const rx_omt_t &referenced_xids) {
    struct referenced_xid_tuple *tuple;
    int r;
    TXNID rval = TXNID_NONE;

    r = referenced_xids.find_zero<TXNID, find_tuple_by_xid>(xc, &tuple, nullptr);
    if (r == DB_NOTFOUND) {
        goto done;
    }
    TXNID live;

    r = snapshot_txnids.find<TXNID, toku_find_xid_by_xid>(tuple->end_id, -1, &live, nullptr);
    if (r == DB_NOTFOUND) {
        goto done;
    }
    invariant(live < tuple->end_id);
    if (live > tuple->begin_id) {
        rval = live;
    }
done:
    return rval;
}

// template-only function, but must be extern
int referenced_xids_note_snapshot_txn_end_iter(const TXNID &live_xid, const uint32_t UU(index), rx_omt_t *const referenced_xids)
    __attribute__((nonnull(3)));
int referenced_xids_note_snapshot_txn_end_iter(const TXNID &live_xid, const uint32_t UU(index), rx_omt_t *const referenced_xids)
{
    int r;
    uint32_t idx;
    struct referenced_xid_tuple *tuple;

    r = referenced_xids->find_zero<TXNID, find_tuple_by_xid>(live_xid, &tuple, &idx);
    if (r == DB_NOTFOUND) {
        goto done;
    }
    invariant_zero(r);
    invariant(tuple->references > 0);
    if (--tuple->references == 0) {
        r = referenced_xids->delete_at(idx);
        lazy_assert_zero(r);
    }
done:
    return 0;
}

// When txn ends, update reverse live list.  To do that, examine each txn in this (closing) txn's live list.
static int
referenced_xids_note_snapshot_txn_end(TXN_MANAGER mgr, const xid_omt_t &live_root_txn_list) {
    int r;
    r = live_root_txn_list.iterate<rx_omt_t, referenced_xids_note_snapshot_txn_end_iter>(&mgr->referenced_xids);
    invariant_zero(r);
    return r;
}

//Heaviside function to find a TOKUTXN by TOKUTXN (used to find the index)
// template-only function, but must be extern
int find_xid (const TOKUTXN &txn, const TOKUTXN &txnfind);
int
find_xid (const TOKUTXN &txn, const TOKUTXN &txnfind)
{
    if (txn->txnid64<txnfind->txnid64) return -1;
    if (txn->txnid64>txnfind->txnid64) return +1;
    return 0;
}

void toku_txn_manager_finish_txn(TXN_MANAGER txn_manager, TOKUTXN txn) {
    int r;
    txn_manager_lock(txn_manager);

    if (garbage_collection_debug) {
        verify_snapshot_system(txn_manager);
    }
    {
        //Remove txn from list (omt) of live transactions
        TOKUTXN txnagain;
        uint32_t idx;
        r = txn_manager->live_txns.find_zero<TOKUTXN, find_xid>(txn, &txnagain, &idx);
        invariant_zero(r);
        invariant(txn==txnagain);
        r = txn_manager->live_txns.delete_at(idx);
        invariant_zero(r);
    }

    bool is_snapshot = (txn->snapshot_type != TXN_SNAPSHOT_NONE && (txn->parent==NULL || txn->snapshot_type == TXN_SNAPSHOT_CHILD));
    uint32_t index_in_snapshot_txnids;
    if (is_snapshot) {
        TXNID xid;
        //Free memory used for snapshot_txnids
        r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, &xid, &index_in_snapshot_txnids);
        invariant_zero(r);
        invariant(xid == txn->txnid64);
        r = txn_manager->snapshot_txnids.delete_at(index_in_snapshot_txnids);
        invariant_zero(r);

        referenced_xids_note_snapshot_txn_end(txn_manager, *txn->live_root_txn_list);

        //Free memory used for live root txns local list (will happen
        //after we unlock the txn_manager_lock)
        invariant(txn->live_root_txn_list->size() > 0);
    }

    if (txn->parent==NULL) {
        TXNID xid;
        uint32_t idx;
        //Remove txn from list of live root txns
        r = txn_manager->live_root_txns.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, &xid, &idx);
        invariant_zero(r);
        invariant(xid == txn->txnid64);
        r = txn_manager->live_root_txns.delete_at(idx);
        invariant_zero(r);

        if (!toku_txn_is_read_only(txn) || garbage_collection_debug) {
            if (!is_snapshot) {
                // If it's a snapshot, we already calculated index_in_snapshot_txnids.
                // Otherwise, calculate it now.
                r = txn_manager->snapshot_txnids.find_zero<TXNID, toku_find_xid_by_xid>(txn->txnid64, nullptr, &index_in_snapshot_txnids);
                invariant(r == DB_NOTFOUND);
            }
            uint32_t num_references = txn_manager->snapshot_txnids.size() - index_in_snapshot_txnids;
            if (num_references > 0) {
                // This transaction exists in a live list of another transaction.
                struct referenced_xid_tuple tuple = {
                    .begin_id = txn->txnid64,
                    .end_id = ++txn_manager->last_xid,
                    .references = num_references
                };
                r = txn_manager->referenced_xids.insert<TXNID, find_tuple_by_xid>(tuple, txn->txnid64, nullptr);
                lazy_assert_zero(r);
            }
        }
    }

    if (garbage_collection_debug) {
        verify_snapshot_system(txn_manager);
    }
    txn_manager_unlock(txn_manager);

    //Cleanup that does not require the txn_manager lock
    if (is_snapshot) {
        invariant(txn->live_root_txn_list != nullptr);
        txn->live_root_txn_list->destroy();
        toku_free(txn->live_root_txn_list);
    }
}

void toku_txn_manager_clone_state_for_gc(
    TXN_MANAGER txn_manager,
    xid_omt_t &snapshot_xids,
    rx_omt_t &referenced_xids,
    xid_omt_t &live_root_txns
    )
{
    txn_manager_lock(txn_manager);
    snapshot_xids.clone(txn_manager->snapshot_txnids);
    referenced_xids.clone(txn_manager->referenced_xids);
    live_root_txns.clone(txn_manager->live_root_txns);
    txn_manager_unlock(txn_manager);
}

void toku_txn_manager_id2txn_unlocked(TXN_MANAGER txn_manager, TXNID txnid, TOKUTXN *result) {
    TOKUTXN txn;
    int r = txn_manager->live_txns.find_zero<TXNID, find_by_xid>(txnid, &txn, nullptr);
    if (r==0) {
        assert(txn->txnid64==txnid);
        *result = txn;
    }
    else {
        assert(r==DB_NOTFOUND);
        // If there is no txn, then we treat it as the null txn.
        *result = NULL;
    }
}

void toku_txn_manager_id2txn(TXN_MANAGER txn_manager, TXNID txnid, TOKUTXN *result) {
    txn_manager_lock(txn_manager);
    toku_txn_manager_id2txn_unlocked(txn_manager, txnid, result);
    txn_manager_unlock(txn_manager);
}

int toku_txn_manager_get_txn_from_xid (TXN_MANAGER txn_manager, TOKU_XA_XID *xid, DB_TXN **txnp) {
    txn_manager_lock(txn_manager);
    int ret_val = 0;
    int num_live_txns = txn_manager->live_txns.size();
    for (int i = 0; i < num_live_txns; i++) {
        TOKUTXN txn;
        {
            int r = txn_manager->live_txns.fetch(i, &txn);
            assert_zero(r);
        }
        if (txn->xa_xid.formatID     == xid->formatID
            && txn->xa_xid.gtrid_length == xid->gtrid_length
            && txn->xa_xid.bqual_length == xid->bqual_length
            && 0==memcmp(txn->xa_xid.data, xid->data, xid->gtrid_length + xid->bqual_length)) {
            *txnp = txn->container_db_txn;
            ret_val = 0;
            goto exit;
        }
    }
    ret_val = DB_NOTFOUND;
exit:
    txn_manager_unlock(txn_manager);
    return ret_val;
}

uint32_t toku_txn_manager_num_live_txns(TXN_MANAGER txn_manager) {
    int ret_val = 0;
    txn_manager_lock(txn_manager);
    ret_val = txn_manager->live_txns.size();
    txn_manager_unlock(txn_manager);
    return ret_val;
}

void toku_txn_manager_add_prepared_txn(TXN_MANAGER txn_manager, TOKUTXN txn) {
    txn_manager_lock(txn_manager);
    assert(txn->state==TOKUTXN_LIVE);
    txn->state = TOKUTXN_PREPARING; // This state transition must be protected against begin_checkpoint
    toku_list_push(&txn_manager->prepared_txns, &txn->prepared_txns_link);
    txn_manager_unlock(txn_manager);
}

static void invalidate_xa_xid (TOKU_XA_XID *xid) {
    HELGRIND_ANNOTATE_NEW_MEMORY(xid, sizeof(*xid)); // consider it to be all invalid for valgrind
    xid->formatID = -1; // According to the XA spec, -1 means "invalid data"
}

void toku_txn_manager_note_abort_txn(TXN_MANAGER txn_manager, TOKUTXN txn) {
    // Purpose:
    //  Delay until any indexer is done pinning this transaction.
    //  Update status of a transaction from live->aborting (or prepared->aborting)
    //  Do so in a thread-safe manner that does not conflict with hot indexing or
    //  begin checkpoint.
    if (toku_txn_is_read_only(txn)) {
        // Neither hot indexing nor checkpoint do any work with readonly txns,
        // so we can skip taking the txn_manager lock here.
        invariant(txn->state==TOKUTXN_LIVE);
        txn->state = TOKUTXN_ABORTING;
        goto done;
    }
    txn_manager_lock(txn_manager);
    if (txn->state==TOKUTXN_PREPARING) {
        invalidate_xa_xid(&txn->xa_xid);
        toku_list_remove(&txn->prepared_txns_link);
    }
    // for hot indexing, if hot index is processing
    // this transaction in some leafentry, then we cannot change
    // the state to commit or abort until
    // hot index is done with that leafentry
    while (txn->num_pin > 0) {
        toku_cond_wait(
            &txn_manager->wait_for_unpin_of_txn,
            &txn_manager->txn_manager_lock
            );
    }
    txn->state = TOKUTXN_ABORTING;
    txn_manager_unlock(txn_manager);
done:
    return;
}

void toku_txn_manager_note_commit_txn(TXN_MANAGER txn_manager, TOKUTXN txn) {
    // Purpose:
    //  Delay until any indexer is done pinning this transaction.
    //  Update status of a transaction from live->committing (or prepared->committing)
    //  Do so in a thread-safe manner that does not conflict with hot indexing or
    //  begin checkpoint.
    if (toku_txn_is_read_only(txn)) {
        // Neither hot indexing nor checkpoint do any work with readonly txns,
        // so we can skip taking the txn_manager lock here.
        invariant(txn->state==TOKUTXN_LIVE);
        txn->state = TOKUTXN_COMMITTING;
        goto done;
    }
    txn_manager_lock(txn_manager);
    if (txn->state==TOKUTXN_PREPARING) {
        invalidate_xa_xid(&txn->xa_xid);
        toku_list_remove(&txn->prepared_txns_link);
    }
    // for hot indexing, if hot index is processing
    // this transaction in some leafentry, then we cannot change
    // the state to commit or abort until
    // hot index is done with that leafentry
    while (txn->num_pin > 0) {
        toku_cond_wait(
            &txn_manager->wait_for_unpin_of_txn, 
            &txn_manager->txn_manager_lock
            );
    }
    txn->state = TOKUTXN_COMMITTING;
    txn_manager_unlock(txn_manager);
done:
    return;
}

//
// This function is called only via env_txn_xa_recover and env_txn_recover.
// See comments for those functions to understand assumptions that 
// can be made when calling this function. Namely, that the system is 
// quiescant, in that we are right after recovery and before user operations
// commence.
//
// I (Zardosht), don't think we take advantage of this fact, as we are holding
// the txn_manager_lock in this function, but in the future we might want
// to take these assumptions into account.
//
int toku_txn_manager_recover_txn (
    TXN_MANAGER txn_manager, 
    struct tokulogger_preplist preplist[/*count*/], 
    long count, 
    long *retp, /*out*/ 
    uint32_t flags
    )
{
    int ret_val = 0;
    txn_manager_lock(txn_manager);
    if (flags==DB_FIRST) {
        // Anything in the returned list goes back on the prepared list.
        while (!toku_list_empty(&txn_manager->prepared_and_returned_txns)) {
            struct toku_list *h = toku_list_head(&txn_manager->prepared_and_returned_txns);
            toku_list_remove(h);
            toku_list_push(&txn_manager->prepared_txns, h);
        }
    } else if (flags!=DB_NEXT) { 
        ret_val = EINVAL;
        goto exit;
    }
    long i;
    for (i=0; i<count; i++) {
        if (!toku_list_empty(&txn_manager->prepared_txns)) {
            struct toku_list *h = toku_list_head(&txn_manager->prepared_txns);
            toku_list_remove(h);
            toku_list_push(&txn_manager->prepared_and_returned_txns, h);
            TOKUTXN txn = toku_list_struct(h, struct tokutxn, prepared_txns_link);
            assert(txn->container_db_txn);
            preplist[i].txn = txn->container_db_txn;
            preplist[i].xid = txn->xa_xid;
        } else {
            break;
        }
    }
    *retp = i;
    ret_val = 0;
exit:
    txn_manager_unlock(txn_manager);
    return ret_val;
}

// needed for hot indexing

// prevents a client thread from transitioning txn from LIVE|PREPAREING -> COMMITTING|ABORTING
// hot indexing may need a transactions to stay in the LIVE|PREPARING state while it processes
// a leafentry.
void toku_txn_manager_pin_live_txn_unlocked(TXN_MANAGER UU(txn_manager), TOKUTXN txn) {
    assert(txn->state == TOKUTXN_LIVE || txn->state == TOKUTXN_PREPARING);
    assert(!toku_txn_is_read_only(txn));
    txn->num_pin++;
}

// allows a client thread to go back to being able to transition txn
// from LIVE|PREPAREING -> COMMITTING|ABORTING
void toku_txn_manager_unpin_live_txn_unlocked(TXN_MANAGER txn_manager, TOKUTXN txn) {
    assert(txn->state == TOKUTXN_LIVE || txn->state == TOKUTXN_PREPARING);
    assert(txn->num_pin > 0);
    txn->num_pin--;
    if (txn->num_pin == 0) {
        toku_cond_broadcast(&txn_manager->wait_for_unpin_of_txn);
    }
}

static void txn_manager_lock(TXN_MANAGER txn_manager) {
    toku_mutex_lock(&txn_manager->txn_manager_lock);
}

static void txn_manager_unlock(TXN_MANAGER txn_manager) {
    toku_mutex_unlock(&txn_manager->txn_manager_lock);
}

void toku_txn_manager_suspend(TXN_MANAGER txn_manager) {
    txn_manager_lock(txn_manager);
}

void toku_txn_manager_resume(TXN_MANAGER txn_manager) {
    txn_manager_unlock(txn_manager);
}

void
toku_txn_manager_set_last_xid_from_logger(TXN_MANAGER txn_manager, TXNID last_xid) {
    invariant(txn_manager->last_xid == TXNID_NONE);
    txn_manager->last_xid = last_xid;
}

void
toku_txn_manager_set_last_xid_from_recovered_checkpoint(TXN_MANAGER txn_manager, TXNID last_xid) {
    txn_manager->last_xid = last_xid;
}

TXNID
toku_txn_manager_get_last_xid(TXN_MANAGER mgr) {
    txn_manager_lock(mgr);
    TXNID last_xid = mgr->last_xid;
    txn_manager_unlock(mgr);
    return last_xid;
}

// Test-only function
void
toku_txn_manager_increase_last_xid(TXN_MANAGER mgr, uint64_t increment) {
    txn_manager_lock(mgr);
    mgr->last_xid += increment;
    txn_manager_unlock(mgr);
}