Cassandra table tombstone不是0

Question

我对cassandra有意见：

if I do nodetool -h 10.169.20.8 cfstats name.name -H

我得到的结果和统计是这样的：

    Read Count: 0
    Read Latency: NaN ms.
    Write Count: 739812
    Write Latency: 0.038670616318740435 ms.
    Pending Flushes: 0
        Table: name
        SSTable count: 10
        Space used (live): 1.48 GB
        Space used (total): 1.48 GB
        Space used by snapshots (total): 0 bytes
        Off heap memory used (total): 3.04 MB
        SSTable Compression Ratio: 0.5047407001982581
        Number of keys (estimate): 701190
        Memtable cell count: 22562
        Memtable data size: 14.12 MB
        Memtable off heap memory used: 0 bytes
        Memtable switch count: 7
        Local read count: 0
        Local read latency: NaN ms
        Local write count: 739812
        Local write latency: 0.043 ms
        Pending flushes: 0
        Bloom filter false positives: 0
        Bloom filter false ratio: 0.00000
        Bloom filter space used: 2.39 MB
        Bloom filter off heap memory used: 2.39 MB
        Index summary off heap memory used: 302.03 KB
        Compression metadata off heap memory used: 366.3 KB
        Compacted partition minimum bytes: 87 bytes
        Compacted partition maximum bytes: 3.22 MB
        Compacted partition mean bytes: 2.99 KB
        Average live cells per slice (last five minutes): 1101.2357892212697
        Maximum live cells per slice (last five minutes): 1109
        Average tombstones per slice (last five minutes): 271.6848030693603
        Maximum tombstones per slice (last five minutes): 1109
        Dropped Mutations: 0 bytes

为什么tombstones的统计数据不是0？我们这里只写Cassandra，没有人删除记录。我们不使用TTL，设置为默认设置。

第二个问题(可能与这个问题有关)-表的行数随机变化，我们不知道是怎么回事。

Answer 1

我不确定有没有办法解释这些墓碑--如果你不做任何删除的话。

我可以提供两种方法来尝试和分析这一点-也许这将有助于更好地理解how是什么以及如何how。

有一个名为sstable2json的工具-它允许获取sstable并将其转储到json -

例如，对于以下架构

cqlsh> describe schema;

CREATE KEYSPACE test WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'}  AND durable_writes = true;

CREATE TABLE test.t1 (
    key text PRIMARY KEY,
    value text
) WITH bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

在具有完整分区的逻辑删除的sstable文件上运行sstable2json提供了以下内容

[
{"key": "key",
 "metadata": {"deletionInfo": {"markedForDeleteAt":1475270192779047,"localDeletionTime":1475270192}},
 "cells": []}
]

在这种情况下，markjer用于使用"key“的分区。

您可以使用的另一种方法(假设tombstone计数正在增加)是使用tcpdump，然后使用wireshark对其进行分析。来自ScyllaDB的Benoit Canet为wireshark贡献了支持CQL的分析器，该分析器现在是最新的稳定版本2.2.0 (https://www.wireshark.org/docs/relnotes/wireshark-2.2.0.html)

请注意，cql删除实际上可以在两种类型中找到:查询和准备(如果删除是使用准备好的语句完成的)。

如果它们是通过预准备语句完成的，则可能需要删除CQL连接，以确保捕获具有预准备语句的特定数据包。

以下是wireshark捕获上述delete语句的示例

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Answer 2

注意:有时可以使用预准备语句中的空值绑定来创建墓碑- http://thelastpickle.com/blog/2016/09/15/Null-bindings-on-prepared-statements-and-undesired-tombstone-creation.html

Answer 3

在列中写入的值与删除相同，并导致逻辑删除。Wait... Say What.