1/*
2 * librdkafka - The Apache Kafka C/C++ library
3 *
4 * Copyright (c) 2015 Magnus Edenhill
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions are met:
9 *
10 * 1. Redistributions of source code must retain the above copyright notice,
11 * this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright notice,
13 * this list of conditions and the following disclaimer in the documentation
14 * and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
17 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
20 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28#include "rdkafka_int.h"
29#include "rdkafka_assignor.h"
30
31
32
33
34
35
36/**
37 * Source: https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/clients/consumer/RangeAssignor.java
38 *
39 * The range assignor works on a per-topic basis. For each topic, we lay out the available partitions in numeric order
40 * and the consumers in lexicographic order. We then divide the number of partitions by the total number of
41 * consumers to determine the number of partitions to assign to each consumer. If it does not evenly
42 * divide, then the first few consumers will have one extra partition.
43 *
44 * For example, suppose there are two consumers C0 and C1, two topics t0 and t1, and each topic has 3 partitions,
45 * resulting in partitions t0p0, t0p1, t0p2, t1p0, t1p1, and t1p2.
46 *
47 * The assignment will be:
48 * C0: [t0p0, t0p1, t1p0, t1p1]
49 * C1: [t0p2, t1p2]
50 */
51
52rd_kafka_resp_err_t
53rd_kafka_range_assignor_assign_cb (rd_kafka_t *rk,
54 const char *member_id,
55 const char *protocol_name,
56 const rd_kafka_metadata_t *metadata,
57 rd_kafka_group_member_t *members,
58 size_t member_cnt,
59 rd_kafka_assignor_topic_t **eligible_topics,
60 size_t eligible_topic_cnt,
61 char *errstr, size_t errstr_size,
62 void *opaque) {
63 unsigned int ti;
64 int i;
65
66 /* The range assignor works on a per-topic basis. */
67 for (ti = 0 ; ti < eligible_topic_cnt ; ti++) {
68 rd_kafka_assignor_topic_t *eligible_topic = eligible_topics[ti];
69 int numPartitionsPerConsumer;
70 int consumersWithExtraPartition;
71
72 /* For each topic, we lay out the available partitions in
73 * numeric order and the consumers in lexicographic order. */
74 rd_list_sort(&eligible_topic->members,
75 rd_kafka_group_member_cmp);
76
77 /* We then divide the number of partitions by the total number of
78 * consumers to determine the number of partitions to assign to
79 * each consumer. */
80 numPartitionsPerConsumer =
81 eligible_topic->metadata->partition_cnt /
82 rd_list_cnt(&eligible_topic->members);
83
84 /* If it does not evenly divide, then the first few consumers
85 * will have one extra partition. */
86 consumersWithExtraPartition =
87 eligible_topic->metadata->partition_cnt %
88 rd_list_cnt(&eligible_topic->members);
89
90 rd_kafka_dbg(rk, CGRP, "ASSIGN",
91 "range: Topic %s with %d partition(s) and "
92 "%d subscribing member(s)",
93 eligible_topic->metadata->topic,
94 eligible_topic->metadata->partition_cnt,
95 rd_list_cnt(&eligible_topic->members));
96
97 for (i = 0 ; i < rd_list_cnt(&eligible_topic->members) ; i++) {
98 rd_kafka_group_member_t *rkgm =
99 rd_list_elem(&eligible_topic->members, i);
100 int start = numPartitionsPerConsumer * i +
101 RD_MIN(i, consumersWithExtraPartition);
102 int length = numPartitionsPerConsumer +
103 (i + 1 > consumersWithExtraPartition ? 0 : 1);
104
105 if (length == 0)
106 continue;
107
108 rd_kafka_dbg(rk, CGRP, "ASSIGN",
109 "range: Member \"%s\": "
110 "assigned topic %s partitions %d..%d",
111 rkgm->rkgm_member_id->str,
112 eligible_topic->metadata->topic,
113 start, start+length-1);
114 rd_kafka_topic_partition_list_add_range(
115 rkgm->rkgm_assignment,
116 eligible_topic->metadata->topic,
117 start, start+length-1);
118 }
119 }
120
121 return 0;
122}
123
124
125
126