LevelDB.m

#import <Objective-LevelDB/LevelDB.h>
#import <Objective-LevelDB/LDBWriteBatch.h>
#include <mach/mach_time.h>
#include <stdint.h>

NSString *randomString(NSUInteger length) {
    NSMutableString *string = [NSMutableString stringWithCapacity:length];
    for (int i = 0; i < length; i++) {
        [string appendFormat:@"%C", (unichar)('a' + arc4random_uniform(25))];
    }
    return string;
}

void benchmarkLevelDB(NSUInteger approach) {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
    NSString *dbPath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"test.ldb"];
    [[NSFileManager defaultManager] removeItemAtPath:dbPath error:nil];

    NSUInteger numberOfObjects = 30000; // 30,000
    NSMutableArray *randomStrings = [NSMutableArray arrayWithCapacity:numberOfObjects * 9];
    NSInteger stringLength = 10;

    for (NSInteger i = 0; i < numberOfObjects * 9; i++) {
        [randomStrings addObject:randomString(stringLength)];
    }

    const uint64_t startTime = mach_absolute_time();

    // Create 30k LevelDB objects
    // Precomputes random strings
    
    LevelDB *ldb = [LevelDB databaseInLibraryWithName:@"test.ldb"];
    if (approach == 0) {
        // Benchmark: 1.93 seconds (!) on iPhone 5
        ldb.encoder = ^ NSData * (LevelDBKey *key, NSArray *values) {
            return [NSJSONSerialization dataWithJSONObject:values options:0 error:NULL];
        };
        
        LDBWritebatch *wb = [ldb newWritebatch];
        
        for (NSInteger i = 0; i < numberOfObjects; i++) {
            NSArray *subArray = [randomStrings subarrayWithRange:NSMakeRange(i * 9, 9)];
            [wb setObject:subArray forKey:[@(i) stringValue]];
        }
        
        [wb apply];
    } else if (approach == 1) {
        // Benchmark: 10.1 seconds on iPhone 5
        ldb.encoder = ^ NSData * (LevelDBKey *key, NSString *value) {
            return [value dataUsingEncoding:NSASCIIStringEncoding];
        };
        
        LDBWritebatch *wb = [ldb newWritebatch];
        
        for (NSInteger i = 0; i < numberOfObjects; i++) {
            NSArray *subArray = [randomStrings subarrayWithRange:NSMakeRange(i * 9, 9)];
            for (NSUInteger j = 0; j < 9; j++) {
                [wb setObject:subArray[j] forKey:[NSString stringWithFormat:@"%ld.%ld", (long)i, (long)j]];
            }
        }
        
        [wb apply];
    }

    const uint64_t endTime = mach_absolute_time();

    const uint64_t elapsedMTU = endTime - startTime;

    // Get information for converting from MTU to nanoseconds
    mach_timebase_info_data_t info;
    mach_timebase_info(&info);

    // Get elapsed time in nanoseconds
    const double elapsedNS = (double)elapsedMTU * (double)info.numer / (double)info.denom;

    [ldb close];
    NSLog(@"adding %lu objects to LevelDB took %.2f seconds", (unsigned long)numberOfObjects, elapsedNS / 1000000000.0f);
}

Overview

Just a quick performance comparison between LevelDB and Realm. Benchmark inserted 30k objects with 9 string properties each, with random strings.

Realm was **3.7 seconds** on average.
LevelDB was **73.6 seconds** on average.

RealmStringsBenchmarks.m

#include <mach/mach_time.h>
#include <stdint.h>

#import <Realm/Realm.h>

@interface ANISampleRealmModel : RLMObject

@property (nonatomic, copy) NSString *testString1;
@property (nonatomic, copy) NSString *testString2;
@property (nonatomic, copy) NSString *testString3;
@property (nonatomic, copy) NSString *testString4;
@property (nonatomic, copy) NSString *testString5;
@property (nonatomic, copy) NSString *testString6;
@property (nonatomic, copy) NSString *testString7;
@property (nonatomic, copy) NSString *testString8;
@property (nonatomic, copy) NSString *testString9;

@property (nonatomic, assign) NSInteger testInteger;

@end

@implementation ANISampleRealmModel
@end

NSString *randomString(NSUInteger length) {
    NSMutableString *string = [NSMutableString stringWithCapacity:length];
    for (int i = 0; i < length; i++) {
        [string appendFormat:@"%C", (unichar)('a' + arc4random_uniform(25))];
    }
    return string;
}

NSArray *generateRandomRealmObjects(NSInteger count) { // in this case: 30,000
    NSMutableArray *objects = [NSMutableArray arrayWithCapacity:count];
    NSInteger stringLength = 10;

    for (NSInteger i = 0; i < count; i++) {
        ANISampleRealmModel *model = [[ANISampleRealmModel alloc] init];
        model.testString1 = randomString(stringLength);
        model.testString2 = randomString(stringLength);
        model.testString3 = randomString(stringLength);
        model.testString4 = randomString(stringLength);
        model.testString5 = randomString(stringLength);
        model.testString6 = randomString(stringLength);
        model.testString7 = randomString(stringLength);
        model.testString8 = randomString(stringLength);
        model.testString9 = randomString(stringLength);

        [objects addObject:model];
    }

    return objects.copy;
}

void benchmarkRealm(void) {
    [[NSFileManager defaultManager] removeItemAtPath:[[RLMRealm defaultRealm] path] error:nil];
    NSUInteger approachType = 0; // 0 == slow, 1 == fast

    NSUInteger numberOfObjects = 30000; // 30,000
    NSMutableArray *randomStrings = [NSMutableArray arrayWithCapacity:numberOfObjects * 9];
    NSInteger stringLength = 10;

    for (NSInteger i = 0; i < numberOfObjects * 9; i++) {
        [randomStrings addObject:randomString(stringLength)];
    }

    const uint64_t startTime = mach_absolute_time();

    RLMRealm *realm = [RLMRealm defaultRealm];

    [realm beginWriteTransaction];

    if (approachType == 0) {
        // Approach where Realm objects are added one by one to an NSMutableArray
        // and then that NSMutableArray is iterated over one by one to add each Realm object
        // to the realm
        // Benchmark: 20 seconds on iPhone 5 (19.67, 20.01, 19.71, 19.87, 20.99, 20.41)
        NSArray *realmObjects = generateRandomRealmObjects(numberOfObjects);
        [realmObjects enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
            [realm addObject:obj];
        }];
    } else {
        // Approach where random strings are pre-computed and
        // Realm objects are created and added directly to the realm, never copied
        // Benchmark: 3.7 seconds on iPhone 5 (3.35, 3.71, 3.93, 3.65, 3.77, 3.74)
        for (NSInteger i = 0; i < numberOfObjects; i++) {
            NSArray *subArray = [randomStrings subarrayWithRange:NSMakeRange(i * 9, 9)];
            ANISampleRealmModel *model = [[ANISampleRealmModel alloc] init];
            model.testString1 = subArray[0];
            model.testString2 = subArray[1];
            model.testString3 = subArray[2];
            model.testString4 = subArray[3];
            model.testString5 = subArray[4];
            model.testString6 = subArray[5];
            model.testString7 = subArray[6];
            model.testString8 = subArray[7];
            model.testString9 = subArray[8];
            
            [realm addObject:model];
        }
    }

    [realm commitWriteTransaction];

    const uint64_t endTime = mach_absolute_time();

    const uint64_t elapsedMTU = endTime - startTime;

    // Get information for converting from MTU to nanoseconds
    mach_timebase_info_data_t info;
    mach_timebase_info(&info);

    // Get elapsed time in nanoseconds
    const double elapsedNS = (double)elapsedMTU * (double)info.numer / (double)info.denom;

    NSLog(@"adding %lu objects to the realm took %.2f seconds", (unsigned long)numberOfObjects, elapsedNS / 1000000000.0f);
}