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lmdb: ITS#7974 get a lag of the reading for dreamcatcher.

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Change-Id: I7fc93ce4fa851904521a58a225f04c65eca2d998
This commit is contained in:
Leo Yuriev 2014-10-21 15:34:22 +04:00
parent 7984f8817f
commit 2df38ad58b
2 changed files with 32 additions and 0 deletions
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12
lmdb.h
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@ -1554,6 +1554,18 @@ int mdb_reader_list(MDB_env *env, MDB_msg_func *func, void *ctx);
* @return 0 on success, non-zero on failure.
*/
int mdb_reader_check(MDB_env *env, int *dead);
/** @brief Returns a lag of the reading.
*
* Returns an information for estimate how much given read-only
* transaction is lagging relative the to actual head.
*
* @param[in] txn A transaction handle returned by #mdb_txn_begin()
* @param[out] percent Percentage of page allocation in the database.
* @return Number of transactions committed after the given was started for read, or -1 on failure.
*/
int mdb_txn_straggler(MDB_txn *txnm, int *percent);
/** @} */
#ifdef __cplusplus

20
mdb.c
View File

@ -2838,6 +2838,26 @@ mdb_dbis_update(MDB_txn *txn, int keep)
env->me_numdbs = n;
}
int
mdb_txn_straggler(MDB_txn *txn, int *percent)
{
MDB_env *env;
MDB_meta *meta;
txnid_t lag;
if (! txn || ! txn->mt_u.reader)
return -1;
env = txn->mt_env;
meta = env->me_metas[ mdb_env_pick_meta(env) ];
if (percent) {
long cent = env->me_maxpg / 100;
*percent = (meta->mm_last_pg + cent / 2 + 1) / (cent ? cent : 1);
}
lag = meta->mm_txnid - txn->mt_u.reader->mr_txnid;
return (0 > (int) lag) ? ~0u >> 1: lag;
}
/** Common code for #mdb_txn_reset() and #mdb_txn_abort().
* May be called twice for readonly txns: First reset it, then abort.
* @param[in] txn the transaction handle to reset