Issue 164 in leveldb: leveldb writes blocks occassionarily

[l***@googlecode.com]

Status: New
Owner: ----
Labels: Type-Defect Priority-Medium

New issue 164 by ***@gmail.com: leveldb writes blocks occassionarily
http://code.google.com/p/leveldb/issues/detail?id=164

What steps will reproduce the problem?
1. download and compile leveldb-1.9.0
2. write a test program test.cpp(in attachment), which makes only Put()
operations.
3. compile and run the test

What is the expected output? What do you see instead?

All write operations should be quick enougth(less than 100ms), there should
not print any slow log.

Here the outputs:

nums: 1000
83: slow log: 7151.075
169: slow log: 106.461
403: slow log: 393.466
487: slow log: 112.986
563: slow log: 117.801

the slowest write operation takes 7151.075 ms!

What version of the product are you using? On what operating system?

Linux xen05.wd.corp.qihoo.net 2.6.18-164.el5xen #1 SMP Thu Sep 3 04:03:03
EDT 2009 x86_64 x86_64 x86_64 GNU/Linux

Please provide any additional information below.

How to compile test.cpp: g++ test.cpp
-I../leveldb-1.9.0/include ../leveldb-1.9.0/libleveldb.a -pthread
Run it: ./a.out
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[l***@googlecode.com]

Comment #1 on issue 164 by ***@gmail.com: leveldb writes blocks
occassionarily
http://code.google.com/p/leveldb/issues/detail?id=164

The attachment may be mission, repost.

{{{
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <time.h>
#include <sys/time.h>

#include <string>

#include "leveldb/db.h"
#include "leveldb/options.h"
#include "leveldb/slice.h"

static inline double microtime(){
struct timeval now;
gettimeofday(&now, NULL);
double ret = now.tv_sec + now.tv_usec/1000.0/1000.0;
return ret;
}
int main(int argc, char **argv){
int nums = 1000;
if(argc > 1){
nums = atoi(argv[1]);
}
printf("nums: %d\n", nums);

leveldb::DB* db;
leveldb::Options options;
leveldb::Status status;
options.create_if_missing = true;
status = leveldb::DB::Open(options, "a", &db);
if(!status.ok()){
printf("open leveldb: %s error!\n", "a");
return 0;
}

char buf[1024];
srand ( time(NULL) );

for(int i=0; i<nums; i++){
snprintf(buf, sizeof(buf), "%d%d", rand(), rand());
std::string k(buf);
std::string v(rand()%(100*1024), 'a');
double stime = microtime();
status = db->Put(leveldb::WriteOptions(), k, v);
double ts = 1000 * (microtime() - stime);
if(ts > 100){
printf("%5d: slow log: %8.3f\n", i, ts);
}
if(!status.ok()){
printf("put leveldb error!\n");
break;
}
}

delete db;
return 0;
}
}}}


Attachments:
test.cpp 1.2 KB
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[l***@googlecode.com]

Comment #2 on issue 164 by ***@gmail.com: leveldb writes blocks
occassionarily
http://code.google.com/p/leveldb/issues/detail?id=164

I put debug codes in db_impl.cc, I can see DBImpl::MakeRoomForWrite(bool
force) takes most of the time.

And these lines got executed many times within one Write:

// There are too many level-0 files.
Log(options_.info_log, "waiting...\n");
bg_cv_.Wait();

As the comment show, I think there is something related to background
compaction thread. Maybe leveldb shouldn't wait for compaction to complete?
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[l***@googlecode.com]

Updates:
Cc: ***@chromium.org

Comment #3 on issue 164 by ***@chromium.org: leveldb writes blocks
occassionarily
http://code.google.com/p/leveldb/issues/detail?id=164

(No comment was entered for this change.)
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[王磊]

I meet the same problem. Has this been solved?

Post by l***@googlecode.com
writes blocks
occassionarily
http://code.google.com/p/leveldb/issues/detail?id=164
(No comment was entered for this change.)
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