lmdbjava/src/test/java/org/lmdbjava/TutorialTest.java at master · lmdbjava/lmdbjava

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* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

package org.lmdbjava;

import static java.nio.charset.StandardCharsets.UTF_8;

import static java.util.concurrent.TimeUnit.SECONDS;

import static org.assertj.core.api.Assertions.assertThat;

import static org.lmdbjava.ByteBufferProxy.PROXY_OPTIMAL;

import static org.lmdbjava.DbiFlags.MDB_CREATE;

import static org.lmdbjava.DbiFlags.MDB_DUPSORT;

import static org.lmdbjava.DbiFlags.MDB_INTEGERKEY;

import static org.lmdbjava.DbiFlags.MDB_REVERSEKEY;

import static org.lmdbjava.DirectBufferProxy.PROXY_DB;

import static org.lmdbjava.GetOp.MDB_SET;

import static org.lmdbjava.SeekOp.MDB_FIRST;

import static org.lmdbjava.SeekOp.MDB_LAST;

import static org.lmdbjava.SeekOp.MDB_PREV;

import java.nio.ByteBuffer;

import java.nio.ByteOrder;

import java.nio.file.Path;

import java.util.ArrayList;

import java.util.List;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import org.agrona.DirectBuffer;

import org.agrona.MutableDirectBuffer;

import org.agrona.concurrent.UnsafeBuffer;

import org.junit.jupiter.api.AfterEach;

import org.junit.jupiter.api.BeforeEach;

import org.junit.jupiter.api.Test;

import org.lmdbjava.CursorIterable.KeyVal;

/**

* Welcome to LmdbJava!

* <p>This short tutorial will walk you through using LmdbJava step-by-step.

* <p>If you are using a 64-bit Windows, Linux or OS X machine, you can simply run this tutorial by

* adding the LmdbJava JAR to your classpath. It includes the required system libraries. If you are

* using another 64-bit platform, you'll need to install the LMDB system library yourself. 32-bit

* platforms are not supported.

* <p>Start the JVM with arguments <code>--add-opens java.base/java.nio=ALL-UNNAMED

* --add-opens java.base/sun.nio.ch=ALL-UNNAMED</code> to suppress JVM warnings.

public final class TutorialTest {

private static final String DB_NAME = "my DB";

private TempDir tempDir;

@BeforeEach

void beforeEach() {

tempDir = new TempDir();

}

@AfterEach

void afterEach() {

tempDir.cleanup();

}

/** In this first tutorial we will use LmdbJava with some basic defaults. */

@Test

void tutorial1() {

// We need a storage directory first.

// The path cannot be on a remote file system.

final Path dir = tempDir.createTempDir();

// We always need an Env. An Env owns a physical on-disk storage file. One

// Env can store many different databases (ie sorted maps).

final Env<ByteBuffer> env =

Env.create()

// LMDB also needs to know how large our DB might be. Over-estimating is OK.

.setMapSize(10_485_760)

// LMDB also needs to know how many DBs (Dbi) we want to store in this Env.

.setMaxDbs(1)

// Now let's open the Env. The same path can be concurrently opened and

// used in different processes, but do not open the same path twice in

// the same process at the same time.

.open(dir);

// We need a Dbi for each DB. A Dbi roughly equates to a sorted map. The

// MDB_CREATE flag causes the DB to be created if it doesn't already exist.

final Dbi<ByteBuffer> db =

env.createDbi().setDbName(DB_NAME).withDefaultComparator().setDbiFlags(MDB_CREATE).open();

// We want to store some data, so we will need a direct ByteBuffer.

// Note that LMDB keys cannot exceed maxKeySize bytes (511 bytes by default).

// Values can be larger.

final ByteBuffer key = ByteBuffer.allocateDirect(env.getMaxKeySize());

final ByteBuffer val = ByteBuffer.allocateDirect(700);

key.put("greeting".getBytes(UTF_8)).flip();

val.put("Hello world".getBytes(UTF_8)).flip();

final int valSize = val.remaining();

// Now store it. Dbi.put() internally begins and commits a transaction (Txn).

db.put(key, val);

// To fetch any data from LMDB we need a Txn. A Txn is very important in

// LmdbJava because it offers ACID characteristics and internally holds a

// read-only key buffer and read-only value buffer. These read-only buffers

// are always the same two Java objects, but point to different LMDB-managed

// memory as we use Dbi (and Cursor) methods. These read-only buffers remain

// valid only until the Txn is released or the next Dbi or Cursor call. If

// you need data afterwards, you should copy the bytes to your own buffer.

try (Txn<ByteBuffer> txn = env.txnRead()) {

final ByteBuffer found = db.get(txn, key);

assertThat(found).isNotNull();

// The fetchedVal is read-only and points to LMDB memory

final ByteBuffer fetchedVal = txn.val();

assertThat(fetchedVal.remaining()).isEqualTo(valSize);

// Let's double-check the fetched value is correct

assertThat(UTF_8.decode(fetchedVal).toString()).isEqualTo("Hello world");

}

// We can also delete. The simplest way is to let Dbi allocate a new Txn...

db.delete(key);

// Now if we try to fetch the deleted row, it won't be present

try (Txn<ByteBuffer> txn = env.txnRead()) {

assertThat(db.get(txn, key)).isNull();

}

env.close();

}

/** In this second tutorial we'll learn more about LMDB's ACID Txns. */

@Test

void tutorial2() {

final Path dir = tempDir.createTempDir();

try {

final Env<ByteBuffer> env = createSimpleEnv(dir);

final Dbi<ByteBuffer> db =

env.createDbi().setDbName(DB_NAME).withDefaultComparator().setDbiFlags(MDB_CREATE).open();

final ByteBuffer key = ByteBuffer.allocateDirect(env.getMaxKeySize());

final ByteBuffer val = ByteBuffer.allocateDirect(700);

// Let's write and commit "key1" via a Txn. A Txn can include multiple Dbis.

// Note write Txns block other write Txns, due to writes being serialized.

// It's therefore important to avoid unnecessarily long-lived write Txns.

try (Txn<ByteBuffer> txn = env.txnWrite()) {

key.put("key1".getBytes(UTF_8)).flip();

val.put("lmdb".getBytes(UTF_8)).flip();

db.put(txn, key, val);

// We can read data too, even though this is a write Txn.

final ByteBuffer found = db.get(txn, key);

assertThat(found).isNotNull();

// An explicit commit is required, otherwise Txn.close() rolls it back.

txn.commit();

}

// Open a read-only Txn. It only sees data that existed at Txn creation time.

final Txn<ByteBuffer> rtx = env.txnRead();

// Our read Txn can fetch key1 without problem, as it existed at Txn creation.

ByteBuffer found = db.get(rtx, key);

assertThat(found).isNotNull();

// Note that our main test thread holds the Txn. Only one Txn per thread is

// typically permitted (the exception is a read-only Env with MDB_NOTLS).

// Let's write out a "key2" via a new write Txn in a different thread.

final ExecutorService es = Executors.newCachedThreadPool();

es.execute(

() -> {

try (Txn<ByteBuffer> txn = env.txnWrite()) {

key.clear();

key.put("key2".getBytes(UTF_8)).flip();

db.put(txn, key, val);

txn.commit();

}

});

es.shutdown();

es.awaitTermination(10, SECONDS);

// Even though key2 has been committed, our read Txn still can't see it.

found = db.get(rtx, key);

assertThat(found).isNull();

// To see key2, we could create a new Txn. But a reset/renew is much faster.

// Reset/renew is also important to avoid long-lived read Txns, as these

// prevent the re-use of free pages by write Txns (ie the DB will grow).

rtx.reset();

// ... potentially long operation here ...

rtx.renew();

found = db.get(rtx, key);

assertThat(found).isNotNull();

// Don't forget to close the read Txn now we're completely finished. We could

// have avoided this if we used a try-with-resources block, but we wanted to

// play around with multiple concurrent Txns to demonstrate the "I" in ACID.

rtx.close();

env.close();

} catch (final InterruptedException e) {

throw new RuntimeException(e);

}

/**

* In this third tutorial we'll have a look at the Cursor. Up until now we've just used Dbi, which

* is good enough for simple cases but unsuitable if you don't know the key to fetch, or want to

* iterate over all the data etc.

@Test

void tutorial3() {

final Path dir = tempDir.createTempDir();

final Env<ByteBuffer> env = createSimpleEnv(dir);

final Dbi<ByteBuffer> db =

env.createDbi().setDbName(DB_NAME).withDefaultComparator().setDbiFlags(MDB_CREATE).open();

final ByteBuffer key = ByteBuffer.allocateDirect(env.getMaxKeySize());

final ByteBuffer val = ByteBuffer.allocateDirect(700);

try (Txn<ByteBuffer> txn = env.txnWrite()) {

// A cursor always belongs to a particular Dbi.

final Cursor<ByteBuffer> c = db.openCursor(txn);

// We can put via a Cursor. Note we're adding keys in a strange order,

// as we want to show you that LMDB returns them in sorted order.

key.put("zzz".getBytes(UTF_8)).flip();

val.put("lmdb".getBytes(UTF_8)).flip();

c.put(key, val);

key.clear();

key.put("aaa".getBytes(UTF_8)).flip();

c.put(key, val);

key.clear();

key.put("ccc".getBytes(UTF_8)).flip();

c.put(key, val);

// We can read from the Cursor by key.

c.get(key, MDB_SET);

assertThat(UTF_8.decode(c.key()).toString()).isEqualTo("ccc");

// Let's see that LMDB provides the keys in appropriate order....

c.seek(MDB_FIRST);

assertThat(UTF_8.decode(c.key()).toString()).isEqualTo("aaa");

c.seek(MDB_LAST);

assertThat(UTF_8.decode(c.key()).toString()).isEqualTo("zzz");

c.seek(MDB_PREV);

assertThat(UTF_8.decode(c.key()).toString()).isEqualTo("ccc");

// Cursors can also delete the current key.

c.delete();

c.close();

txn.commit();

}

// A read-only Cursor can survive its original Txn being closed. This is

// useful if you want to close the original Txn (eg maybe you created the

// Cursor during the constructor of a singleton with a throw-away Txn). Of

// course, you cannot use the Cursor if its Txn is closed or currently reset.

final Txn<ByteBuffer> tx1 = env.txnRead();

final Cursor<ByteBuffer> c = db.openCursor(tx1);

tx1.close();

// The Cursor becomes usable again by "renewing" it with an active read Txn.

final Txn<ByteBuffer> tx2 = env.txnRead();

c.renew(tx2);

c.seek(MDB_FIRST);

// As usual with read Txns, we can reset and renew them. The Cursor does

// not need any special handling if we do this.

tx2.reset();

// ... potentially long operation here ...

tx2.renew();

c.seek(MDB_LAST);

tx2.close();

env.close();

}

/**

* In this fourth tutorial we'll take a quick look at the iterators. These are a more Java

* idiomatic form of using the Cursors we looked at in tutorial 3.

@Test

void tutorial4() {

final Path dir = tempDir.createTempDir();

final Env<ByteBuffer> env = createSimpleEnv(dir);

final Dbi<ByteBuffer> db =

env.createDbi().setDbName(DB_NAME).withDefaultComparator().setDbiFlags(MDB_CREATE).open();

try (Txn<ByteBuffer> txn = env.txnWrite()) {

final ByteBuffer key = ByteBuffer.allocateDirect(env.getMaxKeySize());

final ByteBuffer val = ByteBuffer.allocateDirect(700);

// Insert some data. Note that ByteBuffer order defaults to Big Endian.

// LMDB does not persist the byte order, but it's critical to sort keys.

// If your numeric keys don't sort as expected, review buffer byte order.

val.putInt(100);

key.putInt(1);

db.put(txn, key, val);

key.clear();

key.putInt(2);

db.put(txn, key, val);

key.clear();

// Each iterable uses a cursor and must be closed when finished. Iterate

// forward in terms of key ordering starting with the first key.

try (CursorIterable<ByteBuffer> ci = db.iterate(txn, KeyRange.all())) {

for (final KeyVal<ByteBuffer> kv : ci) {

assertThat(kv.key()).isNotNull();

assertThat(kv.val()).isNotNull();

}

// Iterate backward in terms of key ordering starting with the last key.

try (CursorIterable<ByteBuffer> ci = db.iterate(txn, KeyRange.allBackward())) {

for (final KeyVal<ByteBuffer> kv : ci) {

assertThat(kv.key()).isNotNull();

assertThat(kv.val()).isNotNull();

}

// There are many ways to control the desired key range via KeyRange, such

// as arbitrary start and stop values, direction etc. We've adopted Guava's

// terminology for our range classes (see KeyRangeType for further details).

key.putInt(1);

final KeyRange<ByteBuffer> range = KeyRange.atLeastBackward(key);

try (CursorIterable<ByteBuffer> ci = db.iterate(txn, range)) {

for (final KeyVal<ByteBuffer> kv : ci) {

assertThat(kv.key()).isNotNull();

assertThat(kv.val()).isNotNull();

}

env.close();

}

/** In this fifth tutorial we'll explore multiple values sharing a single key. */

@Test

void tutorial5() {

final Path dir = tempDir.createTempDir();

final Env<ByteBuffer> env = createSimpleEnv(dir);

// This time we're going to tell the Dbi it can store > 1 value per key.

// There are other flags available if we're storing integers etc.

final Dbi<ByteBuffer> db =

env.createDbi()

.setDbName(DB_NAME)

.withDefaultComparator()

.setDbiFlags(MDB_CREATE, MDB_DUPSORT)

.open();

// Duplicate support requires both keys and values to be <= max key size.

final ByteBuffer key = ByteBuffer.allocateDirect(env.getMaxKeySize());

final ByteBuffer val = ByteBuffer.allocateDirect(env.getMaxKeySize());

try (Txn<ByteBuffer> txn = env.txnWrite()) {

final Cursor<ByteBuffer> c = db.openCursor(txn);

// Store one key, but many values, and in non-natural order.

key.put("key".getBytes(UTF_8)).flip();

val.put("xxx".getBytes(UTF_8)).flip();

c.put(key, val);

val.clear();

val.put("kkk".getBytes(UTF_8)).flip();

c.put(key, val);

val.clear();

val.put("lll".getBytes(UTF_8)).flip();

c.put(key, val);

// Cursor can tell us how many values the current key has.

final long count = c.count();

assertThat(count).isEqualTo(3L);

// Let's position the Cursor. Note sorting still works.

c.seek(MDB_FIRST);

assertThat(UTF_8.decode(c.val()).toString()).isEqualTo("kkk");

c.seek(MDB_LAST);

assertThat(UTF_8.decode(c.val()).toString()).isEqualTo("xxx");

c.seek(MDB_PREV);

assertThat(UTF_8.decode(c.val()).toString()).isEqualTo("lll");

c.close();

txn.commit();

}

env.close();

}

/**

* Next up we'll show you how to easily check your platform (operating system and Java version) is

* working properly with LmdbJava and the embedded LMDB native library.

@Test

void tutorial6() {

final Path dir = tempDir.createTempDir();

// Note we need to specify the Verifier's DBI_COUNT for the Env.

final Env<ByteBuffer> env =

Env.create(PROXY_OPTIMAL)

.setMapSize(10, ByteUnit.MEBIBYTES)

.setMaxDbs(Verifier.DBI_COUNT)

.open(dir);

// Create a Verifier (it's a Callable<Long> for those needing full control).

final Verifier v = new Verifier(env);

// We now run the verifier for 3 seconds; it raises an exception on failure.

// The method returns the number of entries it successfully verified.

v.runFor(3, SECONDS);

env.close();

}

/** In this final tutorial we'll look at using Agrona's DirectBuffer. */

@Test

void tutorial7() {

final Path dir = tempDir.createTempDir();

// The critical difference is we pass the PROXY_DB field to Env.create().

// There's also a PROXY_SAFE if you want to stop ByteBuffer's Unsafe use.

// Aside from that and a different type argument, it's the same as usual...

final Env<DirectBuffer> env =

Env.create(PROXY_DB).setMapSize(10, ByteUnit.MEBIBYTES).setMaxDbs(1).open(dir);

final Dbi<DirectBuffer> db =

env.createDbi().setDbName(DB_NAME).withDefaultComparator().setDbiFlags(MDB_CREATE).open();

final ByteBuffer keyBb = ByteBuffer.allocateDirect(env.getMaxKeySize());

final MutableDirectBuffer key = new UnsafeBuffer(keyBb);

final MutableDirectBuffer val = new UnsafeBuffer(ByteBuffer.allocateDirect(700));

try (Txn<DirectBuffer> txn = env.txnWrite()) {

try (Cursor<DirectBuffer> c = db.openCursor(txn)) {

// Agrona is faster than ByteBuffer and its methods are nicer...

val.putStringWithoutLengthUtf8(0, "The Value");

key.putStringWithoutLengthUtf8(0, "yyy");

c.put(key, val);

key.putStringWithoutLengthUtf8(0, "ggg");

c.put(key, val);

c.seek(MDB_FIRST);

assertThat(c.key().getStringWithoutLengthUtf8(0, env.getMaxKeySize())).startsWith("ggg");

c.seek(MDB_LAST);

assertThat(c.key().getStringWithoutLengthUtf8(0, env.getMaxKeySize())).startsWith("yyy");

// DirectBuffer has no position concept. Often you don't want to store

// the unnecessary bytes of a varying-size buffer. Let's have a look...

final int keyLen = key.putStringWithoutLengthUtf8(0, "12characters");

assertThat(keyLen).isEqualTo(12);

assertThat(key.capacity()).isEqualTo(env.getMaxKeySize());

// To only store the 12 characters, we simply call wrap:

key.wrap(key, 0, keyLen);

assertThat(key.capacity()).isEqualTo(keyLen);

c.put(key, val);

c.seek(MDB_FIRST);

assertThat(c.key().capacity()).isEqualTo(keyLen);

assertThat(c.key().getStringWithoutLengthUtf8(0, c.key().capacity()))

.isEqualTo("12characters");

// To store bigger values again, just wrap the original buffer.

key.wrap(keyBb);

assertThat(key.capacity()).isEqualTo(env.getMaxKeySize());

}

txn.commit();

}

env.close();

}

/**

* In this tutorial we'll look at using keys that are longs. The same approach applies would apply

* to int keys.

@Test

void tutorial8() {

final Path dir = tempDir.createTempDir();

final Env<ByteBuffer> env = createSimpleEnv(dir);

// This time we're going to tell the Dbi that all the keys are integers.

// MDB_INTEGERKEY applies to both int and long keys.

// LMDB can make optimisations for better performance.

final Dbi<ByteBuffer> db =

env.createDbi()

.setDbName(DB_NAME)

.withDefaultComparator()

.setDbiFlags(MDB_CREATE, MDB_INTEGERKEY)

.open();

// MDB_INTEGERKEY requires that the keys are written/read in native order

final ByteBuffer key = ByteBuffer.allocateDirect(Long.BYTES).order(ByteOrder.nativeOrder());

final ByteBuffer val = ByteBuffer.allocateDirect(100);

try (Txn<ByteBuffer> txn = env.txnWrite()) {

// Store one key, but many values, and in non-natural order.

key.putLong(42L).flip();

val.put("val-42".getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.putLong(1L).flip();

val.put("val-1".getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.putLong(Long.MAX_VALUE).flip();

val.put(("val-" + Long.MAX_VALUE).getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.putLong(1_000L).flip();

val.put("val-1".getBytes(UTF_8)).flip();

db.put(txn, key, val);

// Get all the keys

final List<Long> keys = new ArrayList<>();

try (CursorIterable<ByteBuffer> ci = db.iterate(txn, KeyRange.all())) {

for (final KeyVal<ByteBuffer> kv : ci) {

assertThat(kv.key()).isNotNull();

assertThat(kv.val()).isNotNull();

keys.add(kv.key().order(ByteOrder.nativeOrder()).getLong());

}

assertThat(keys).containsExactly(1L, 42L, 1_000L, Long.MAX_VALUE);

txn.commit();

}

env.close();

}

/** In this tutorial we'll look storing the data in reverse order */

@Test

void tutorial9() {

final Path dir = tempDir.createTempDir();

final Env<ByteBuffer> env = createSimpleEnv(dir);

final Dbi<ByteBuffer> db =

env.createDbi()

.setDbName(DB_NAME)

.withDefaultComparator()

.setDbiFlags(MDB_CREATE, MDB_REVERSEKEY)

.open();

final ByteBuffer key = ByteBuffer.allocateDirect(100);

final ByteBuffer val = ByteBuffer.allocateDirect(100);

try (Txn<ByteBuffer> txn = env.txnWrite()) {

// Store one key, but many values, and in non-natural order.

key.put("tac".getBytes(UTF_8)).flip();

val.put("CAT".getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.put("god".getBytes(UTF_8)).flip();

val.put("DOG".getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.put("esroh".getBytes(UTF_8)).flip();

val.put("HORSE".getBytes(UTF_8)).flip();

db.put(txn, key, val);

key.clear();

val.clear();

key.put("tnahpele".getBytes(UTF_8)).flip();

val.put("ELEPHANT".getBytes(UTF_8)).flip();

db.put(txn, key, val);

// Get all the keys

final List<String> keys = new ArrayList<>();

final List<String> values = new ArrayList<>();

try (CursorIterable<ByteBuffer> ci = db.iterate(txn, KeyRange.all())) {

for (final KeyVal<ByteBuffer> kv : ci) {

assertThat(kv.key()).isNotNull();

assertThat(kv.val()).isNotNull();

keys.add(UTF_8.decode(kv.key()).toString());

values.add(UTF_8.decode(kv.val()).toString());

}

assertThat(keys).containsExactly("tac", "god", "tnahpele", "esroh");

assertThat(values).containsExactly("CAT", "DOG", "ELEPHANT", "HORSE");

txn.commit();

}

env.close();

}

// You've finished! There are lots of other neat things we could show you (eg

// how to speed up inserts by appending them in key order, using integer

// or reverse ordered keys, using Env.DISABLE_CHECKS_PROP etc), but you now

// know enough to tackle the JavaDocs with confidence. Have fun!

private Env<ByteBuffer> createSimpleEnv(final Path path) {

return Env.create().setMapSize(10, ByteUnit.MEBIBYTES).setMaxDbs(1).setMaxReaders(1).open(path);

}

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