monetdbsolutions / monetdbe-examples Goto Github PK

At cache.c example:

monetdbe_query(remote, "call sys.describe("sys","lineitem"", &schema);

There's a closing parenthesis missing,

In the myserver.c there is a call to monetdbe_listen(). However the monetdbe_listen() is not defined in monetdbe.h.

Further, there is a call to monetdb_error(). I guess that should be monetdbe_error()...

I am trying to access a monetdb-server on another machine in order to initiate a local embedded database with some initial values (C/C++).

However, the cache.c example accessing a remote database seems not to be up to date w.r.t the interface.

E.g. in

monetdbe_open(&remote, "monetdb://localhost:5000/sf1?user=monetdb&password=monetdb");

clearly a NULL is missing in the monetdbe_open(..., NULL) for the Option. However, adding the missing NULL does not seems to make the example work w.r.t be able to connect to the remote database.

Digging into the monetdbe.c, it seems to me like in order to force the monetdbe_open() to try to connect to a remote database, the remote-structure in the Option-structure needs to be filled in.

It would be of great help if you please could update the cache.c example and/or clarify how to connect to a remote named database.

If the option + remote struct has to be used: The remote struct seems to only have variable names for host, port, username, pw and language. How do one enter the database name ("sf1" in the cache-example or "demo" in the example below)?

To be specific, in the full monetdb-version we have e.g:
dbh = mapi_connect("192.168.1.21", 50000, "monetdb", "monetdb", "sql", "demo");

How would the equivalent monetdbe look like?

I was trying to build monetDB Oct2020-SP from source on a RPi4B+ with Ubuntu 20.04 LTS, 64 bit.
The procedure I used to follow, which have worked on all versions previous to Oct2020, was:

export MonetDB_rel=Oct2020-SP3
export MonetDB_ver=11.39.13
export MonetDB_base_dir=$HOME/MonetDB-$MonetDB_rel
export MonetDB_source_dir=$MonetDB_base_dir/MonetDB-$MonetDB_ver
export MonetDB_build_dir=$MonetDB_base_dir/BUILD
export MonetDB_prefix_dir=$MonetDB_base_dir
mkdir $MonetDB_base_dir
cd $MonetDB_base_dir

wget https://dev.monetdb.org/downloads/sources/$MonetDB_rel/MonetDB-11.39.13.tar.xz
tar xf MonetDB-$MonetDB_ver.tar.xz
mkdir $MonetDB_build_dir
cd $MonetDB_build_dir

$MonetDB_source_dir/configure --prefix=$MonetDB_prefix_dir

However the last line results in the error:

-bash: /home/ubuntu/MonetDB-Oct2020-SP3/MonetDB-11.39.13/configure: No such file or directory

It seems like the build process is changed (https://www.monetdb.org/blog/from_automake_to_cmake), but without an updated doc (https://www.monetdb.org/Developers/SourceCompile).

To me it seems like the following is ok (after sudo apt install cmake bison):

export MonetDB_rel=Oct2020-SP3
export MonetDB_ver=11.39.13
export MonetDB_base_dir=$HOME/MonetDB-$MonetDB_rel
export MonetDB_source_dir=$MonetDB_base_dir/MonetDB-$MonetDB_ver
export MonetDB_prefix_dir=$MonetDB_base_dir

mkdir $MonetDB_base_dir
cd $MonetDB_base_dir

wget https://dev.monetdb.org/downloads/sources/$MonetDB_rel/MonetDB-11.39.13.tar.xz

tar xf MonetDB-$MonetDB_ver.tar.xz

cd $MonetDB_source_dir
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
cmake --build .  --parallel -j 4

However, how do one install the compiled version? The old one had e.g.

make -j4 install

Is the one below the right one to use?

sudo cmake --build . --target install --config Release --parallel -j 4

in dbgen.c decimal data types are declared as double but in monetdbe they should be integer data types

((double*)t->cols[i]->data)[k] = s->acctbal;
https://github.com/MonetDBSolutions/monetdbe-examples/blob/master/third_party/dbgen/dbgen.c#L689

The current monetdbe_bind requires the input data too match the parameter /argument of the query. For decimal types the physical type could be any integer (bte,sht,int,lng,hge) with a scale. This is however hard too guess. So we probably need a more flexible interface, including the passed type to monetdbe_bind. That however requires conversion (sometimes)

Tried to build the C-code on a 32bit RPi 4B, Bullseye, 4GB ram.
Latest version pr 11-aug-2023 (git clone https://github.com/MonetDB/MonetDB MonetDBe)
FYI: It builds without errors on 64 bit RPi 4B, Bullseye 8GB ram.

cmake --build .
Scanning dependencies of target moptions
[ 0%] Building C object common/options/CMakeFiles/moptions.dir/monet_options.c.o
[ 0%] Linking C static library libmoptions.a
[ 0%] Built target moptions
Scanning dependencies of target stream
[ 1%] Building C object common/stream/CMakeFiles/stream.dir/stream.c.o
In file included from /home/pi/MonetDBe/common/stream/stream_internal.h:19,
from /home/pi/MonetDBe/common/stream/stream.c:58:
/home/pi/MonetDBe/common/utils/matomic.h:90:2: error: #error "we need _Atomic(unsigned long long) to be lock free"
90 | #error "we need _Atomic(unsigned long long) to be lock free"

gmake[2]: *** [common/stream/CMakeFiles/stream.dir/build.make:82: common/stream/CMakeFiles/stream.dir/stream.c.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:2509: common/stream/CMakeFiles/stream.dir/all] Error 2
gmake: *** [Makefile:182: all] Error 2

matomic.h:

#if SIZEOF_LONG_LONG == 8
#if ATOMIC_LLONG_LOCK_FREE != 2
#error "we need _Atomic(unsigned long long) to be lock free"
#endif
typedef volatile atomic_ullong ATOMIC_TYPE;
typedef unsigned long long ATOMIC_BASE_TYPE;
#elif SIZEOF_LONG == 8
#if ATOMIC_LONG_LOCK_FREE != 2
#error "we need _Atomic(unsigned long) to be lock free"
#endif
typedef volatile atomic_ulong ATOMIC_TYPE;
typedef unsigned long ATOMIC_BASE_TYPE;
#else
#error "we need a 64 bit atomic type"
#endif

Other build info:

cmake -DCMAKE_BUILD_TYPE=Release ..
-- The C compiler identification is GNU 10.2.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
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-- Check size of unsigned short - done
-- Searching 16 bit integer - Using unsigned short
-- Check if the system is big endian - little endian
-- Found BISON: /usr/bin/bison (found version "3.7.5")
-- Performing Test Iconv_IS_BUILT_IN
-- Performing Test Iconv_IS_BUILT_IN - Success
-- Found Iconv: /usr/lib/arm-linux-gnueabihf/libc.so
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-- Looking for pthread.h - found
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-- Found Threads: TRUE
-- Found Python3: /usr/bin/python3.9 (found version "3.9.2") found components: Interpreter Development NumPy Development.Module Development.Embed
-- Could NOT find LibLZMA (missing: LIBLZMA_LIBRARY LIBLZMA_INCLUDE_DIR LIBLZMA_HAS_AUTO_DECODER LIBLZMA_HAS_EASY_ENCODER LIBLZMA_HAS_LZMA_PRESET)
-- Could NOT find LibXml2 (missing: LIBXML2_LIBRARY LIBXML2_INCLUDE_DIR)
-- Found PCRE: /usr/lib/arm-linux-gnueabihf/libpcre.so
-- Could NOT find BZip2 (missing: BZIP2_LIBRARIES BZIP2_INCLUDE_DIR)
-- Found CURL: /usr/lib/arm-linux-gnueabihf/libcurl.so (found version "7.74.0")
-- Found ZLIB: /usr/lib/arm-linux-gnueabihf/libz.so (found version "1.2.11")
-- Could NOT find LZ4 (missing: LZ4_LIBRARIES LZ4_INCLUDE_DIR) (Required is at least version "1.8.0")
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The examples indicates that in monetdbe_open() the second argument is a string for the db directory or NULL for in-memory mode.

The following inmemory works ok:

monetdbe_database db = NULL;
monetdbe_open(&db, NULL /* inmemory database /, NULL / no options */);

However, this one (and any variants) fails:

monetdbe_open(&db, "mydbdir/", NULL /* no options */);

Is there an example of how to open a db with persistency, or is it a bug?

I am testing MonetDBe in a multi threaded application (C++/Linux), where some threads insert data into the database and other threads read.

In your blog about MonetDBe you claim that MonetDBe is thread safe. However, for the time being it seems to me that I have to protect the database access by using a mutex to avoid segfault (testing with in-memory database, i.e no persistence).

Do you have any thoughts about that? Are there any implementation guidelines to follow for using MonetDBe in a threaded application where different threads access the in-memory database? I am using a global variabel monetdbe_database _db referencing the opened in-memory database (and hence accessible for all threads).

A sort of pseudo code (sorry about the messy formatting):

`
monetdbe_database _dbe = NULL;
mutex monetdbeMutex;
bool _sysRunning = false;

int monetDBeCreateDB(){
	monetdbe_options dbOptions;
	dbOptions.memorylimit    = 1000;
	dbOptions.querytimeout   = 60;
	dbOptions.sessiontimeout = 60; 
	dbOptions.nr_threads     = 4;

	char *msg= NULL;

	int statusDB = monetdbe_open(&_dbe, NULL /*pathDB*/, &dbOptions);
	if (statusDB < 0){
		return statusDB;
	} 

	msg = monetdbe_query(_dbe, "CREATE TABLE table0 (t bigint, x0 double, x1 double, x2 double, x3 double, x4 double, x5 double, x6 double);", NULL, NULL);
	if (msg != NULL) printf("%s\n", msg);

	msg = monetdbe_query(_dbe, "CREATE TABLE table1 (t bigint, y0 double, y1 double, y2 double, y3 double);", NULL, NULL);
	if (msg != NULL) printf("%s\n", msg);

	msg = monetdbe_query(_dbe, "CREATE TABLE table2   (t bigint, y0 double, y1 double, y2 double, y3 double);", NULL, NULL);
	if (msg != NULL) printf("%s\n", msg);

	msg = monetdbe_query(_dbe, "CREATE TABLE table3    (t bigint, u0 double, u1 double, u2 double, u3 double, u4 double);", NULL, NULL);
	if (msg != NULL) printf("%s\n", msg);

	return statusDB;
}

void thread0(){
  
   char* msg = NULL;
   monetdbe_result *result;

   while (_sysRunning){
		this_thread::sleep_for(chrono::milliseconds(10000));
    	if (_dbe != NULL){
		    monetdbeMutex.lock();
		    msg = monetdbe_query(_dbe, "SELECT sys.epoch(t) as t_utc,* FROM table0 order by t desc limit 10;", &result, NULL);
			monetdbeMutex.unlock();

			if ( msg == NULL) {
				//do something with the data

			}

		    monetdbeMutex.lock();
			monetdbe_cleanup_result(_dbe, result);
			monetdbeMutex.unlock();
		}
	}
}

void thread1(){
  
   char* msg = NULL;
   string dbQueryStr;
   int64_t rows_affected;  

   while (_sysRunning){
        this_thread::sleep_for(chrono::milliseconds(1000));
    	if (_dbe != NULL){
			dbQueryStr  = "INSERT INTO table0 (t,x0,x1,x2,x3,x4,x5,x6) VALUES (" ... some values ... ");"; 	
			dbQueryStr += "INSERT INTO table1 (t,y0,y1,y2,y3) VALUES ("        ... som values ... ");"; 	            	
			dbQueryStr += "INSERT INTO table2 (t,u0,u1,u2,u3,u4) VALUES ("      ... some values ... ");"; 	            	
			dbQueryStr += "INSERT INTO table3 (t,y0,y1,y2,y3) VALUES (" ... some values ... ");"; 	   

			monetdbeMutex.lock();
			msg = monetdbe_query(_dbe, (char *)dbQueryStr.c_str(), NULL, &rows_affected); 
			monetdbeMutex.unlock();

			if (msg != NULL) {
	                        printf("%s\n",dbQueryStr.c_str());
				printf("%s\n", msg);
			}
    	}
    } //while
}


int main(int argc, char **ppArgv){

	if (monetDBeCreateDB() >= 0){
		_sysRunning = true;     //must be set false by e.g. a sighandler to stop the application
		threads.push_back(std::thread(thread0)); 
		threads.push_back(std::thread(thread1)); 
	}

 	while (_sysRunning){
		this_thread::sleep_for(chrono::milliseconds(60000));
 	}
        if (_dbe != NULL){
             monetdbe_close(_dbe);
            _dbe = NULL;
          }
}

`

In the code like above, if the mutex protection are removed, the application segfaults after a while.

Tested on RPi4B, g++.

the schema type is INT while the monetdbe type is int64