Hi all,
First, I'm having trouble finding resources to answer a question like this myself, so please forgive me if I've missed something.
I'm considering using LMDB (versus LevelDB) for a project I'm working on where I'll be receiving a high volume (hundreds per second) of high priority requests (over HTTP) and issuing multiple (<10) database queries per request.
I'll also have a separate process receiving updates for the data and writing to the database. This will happen often (several times a minute, perhaps), but the priority is much lower than the read requests.
LMDB appealed to me because of the read performance and that I could have one processing reading data from LMDB and another process writing data updates to LMDB.
For proof of concept, I hacked up the following (I'll use pseudocode since I used the Go bindings for my actual programs, and hopefully my question is sufficiently abstract not to matter):
Process 1, the writer, simply writes a random integer (from 0 to 1000) to a defined set of keys:
env = NewEnv() env.Open("/tmp/foo", 0, 0664) txn = env.BeginTxn(nil, 0) dbi = txn.DBIOpen(nil, 0) txn.Commit()
txn = env.BeginTxn(nil, 0) n_entries = 5 for i = 0; i < n_entries; i++ { key = sprintf("Key-%d", i) val = sprintf("Val-%d", rand.Int(1000)) txn.Put(dbi, key, val, 0) } txn.Commit() env.DBIClose(dbi) env.Close()
Process 2, the reader, simply loops forever and does random access reads on the data from process 1 (I won't benefit from a cursor for my actual problem), and prints out that data occasionally:
env = NewEnv() env.Open("/tmp/foo", 0, 0664) while { txn = BeginTxn(nil, 0) dbi = txn.DBIOpen(nil, 0) txn.Commit() for i = 0; i < n_entries; i++ { key = sprintf("Key-%d", i) val = txn.Get(dbi, key) print("%s: %s", key, value) } env.DBIClose(dbi) sleep(5) }
So my high level question is: What am I doing wrong? This seems to work OK, but a lot of it was guesswork, so I'm sure I'm doing some silly things.
For example, first I put the BeginTxn() and DBIOpen() calls in process 2 outside of the while loop, but when I did that, I never saw the updates values upon running process 1 simultaneously. In my real-world application, it seems like adding these calls to every request (to be sure the data being read is up-to-date) could be an unnecessary performance penalty.
I was suspect there are flags that I can/should be using, but I'm not sure.
Thanks for any input.
Brian