Re: (ITS#9060) lmdb corruption after many memory map resizes

[hyc@symas.com]

ruan.declercq@netronome.com wrote:
> Full_Name: Ruan de Clercq
> Version: 
> OS: Ubuntu 19.04
> URL: ftp://ftp.openldap.org/incoming/
> Submission from: (NULL) (155.93.214.171)
> 
> 
> Hi,
> 
> I am using 0.9.23-0ubuntu1 on ubuntu 19.04. 
> 
> I have an application where the exact db size isn't known beforehand. Therefore,
> I set the memory map size beforehand, and then increase the size when I run out
> of space.

This is incorrect usage of LMDB. The docs explicitly state to use a large size at
the beginning and leave it alone.

> However, when I use lmdb in concurrent processes, and frequently
> increase the size of the memory map, I eventually get a corrupt database
> (MDB_CORRUPTED).

Your code is incorrect. The docs explicitly state that there must not be any outstanding
activity when using the set_mapsize call.

Closing this ITS.
>
 Here's a minimal code example:
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <inttypes.h>
> #include <time.h>
> #include "lmdb.h"
> #include <cstring>
> 
> int resize(MDB_env *env) {
>   // read map size and increase
>   int val;
>   MDB_envinfo stat;
>   MDB_txn *txn;
>   if ((val = mdb_env_info(env, &stat) != MDB_SUCCESS) ||
>       (val = mdb_env_set_mapsize(env, stat.me_mapsize + 4096) != MDB_SUCCESS)
> ||
>       (val = mdb_env_info(env, &stat) != MDB_SUCCESS)) {
>     printf("set new mapsize %d\n", val);
>     return val;
>   }
>   printf("Resized to %lu\n", stat.me_mapsize);
>   if (((val = mdb_txn_begin(env, NULL, 0, &txn) != MDB_SUCCESS)) ||
>       ((val = mdb_txn_commit(txn)))) {
>     printf("txn %d\n", val);
>   }
>   return val;
> }
> 
> int main(int argc,char * argv[])
> {
>   timespec tp;
>   clock_gettime(CLOCK_MONOTONIC, &tp);
>   srand(tp.tv_sec + tp.tv_nsec);
> 
>   MDB_env *env = NULL;
>   MDB_txn *txn = NULL;
>   MDB_dbi dbi;
>   int val;
>   if ((val = mdb_env_create(&env) != MDB_SUCCESS) ||
>       (val = mdb_env_set_maxreaders(env, 126) != MDB_SUCCESS)) {
>     printf("Create error %d", val);
>     goto out;
>   }
> 
>   if ((val = mdb_env_set_mapsize(env, 4096 * 128) != MDB_SUCCESS) ||
>       (val = mdb_env_set_maxdbs(env, 1) != MDB_SUCCESS) ||
>       (val = mdb_env_open(env, "./data/", MDB_MAPASYNC | MDB_WRITEMAP, 0664) !=
> MDB_SUCCESS) ||
>       (val = mdb_txn_begin(env, NULL, 0, &txn) != MDB_SUCCESS) ||
>       (val = mdb_dbi_open(txn, "test", MDB_CREATE, &dbi) != MDB_SUCCESS) ||
>       (val = mdb_txn_commit(txn) != MDB_SUCCESS)) {
>     printf("create db %d\n", val);
>     goto out;
>   }
> 
>   for (int i = 0; i < 1000; i++) {
>     char sval[32];
>     sprintf(sval, "%03x %d foo bar", 32, rand());
>     MDB_val mdb_key, mdb_val;
>     mdb_key.mv_size = strlen(sval);;
>     mdb_key.mv_data = sval;
>     mdb_val.mv_size = strlen(sval);
>     mdb_val.mv_data = sval;
> 
>     if ((val = mdb_txn_begin(env, NULL, 0, &txn) != MDB_SUCCESS)) {
>       printf("mdb_txn_begin %d\n", val);
>       goto out;
>     }
>     if ((val = mdb_put(txn, dbi, &mdb_key, &mdb_val, 0)) != MDB_SUCCESS) {
>       mdb_txn_commit(txn);
>       if (val == MDB_MAP_FULL) {
>         val = resize(env);
>         continue;
>       }
>       printf("mdb_put %d\n", val);
>       goto out;
>     }
>     if ((val = mdb_txn_commit(txn)) != MDB_SUCCESS) {
>       if (val == MDB_MAP_FULL) {
>         val = resize(env);
>         continue;
>       }
>       printf("mdb_txn_commit %d\n", val);
>       goto out;
>     }
>   }
> out:
>   if (env) {
>     mdb_dbi_close(env, dbi);
>     mdb_env_close(env);
>   }
>   printf("OK\n");
> }
> 
> After compiling I run the following command a couple of times:
> for i in {1..20}; do echo $i; (lmdb_test &); done
> 
> 


-- 
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/