From hdfs-issues-return-264240-archive-asf-public=cust-asf.ponee.io@hadoop.apache.org Sat May 25 20:20:06 2019 Return-Path: X-Original-To: archive-asf-public@cust-asf.ponee.io Delivered-To: archive-asf-public@cust-asf.ponee.io Received: from mail.apache.org (hermes.apache.org [207.244.88.153]) by mx-eu-01.ponee.io (Postfix) with SMTP id 6456218065D for ; Sat, 25 May 2019 22:20:06 +0200 (CEST) Received: (qmail 12855 invoked by uid 500); 25 May 2019 20:20:05 -0000 Mailing-List: contact hdfs-issues-help@hadoop.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Delivered-To: mailing list hdfs-issues@hadoop.apache.org Received: (qmail 12815 invoked by uid 99); 25 May 2019 20:20:05 -0000 Received: from mailrelay1-us-west.apache.org (HELO mailrelay1-us-west.apache.org) (209.188.14.139) by apache.org (qpsmtpd/0.29) with ESMTP; Sat, 25 May 2019 20:20:05 +0000 Received: from jira-lw-us.apache.org (unknown [207.244.88.139]) by mailrelay1-us-west.apache.org (ASF Mail Server at mailrelay1-us-west.apache.org) with ESMTP id E61BDE02BE for ; Sat, 25 May 2019 20:20:00 +0000 (UTC) Received: from jira-lw-us.apache.org (localhost [127.0.0.1]) by jira-lw-us.apache.org (ASF Mail Server at jira-lw-us.apache.org) with ESMTP id A271820FEB for ; Sat, 25 May 2019 20:20:00 +0000 (UTC) Date: Sat, 25 May 2019 20:20:00 +0000 (UTC) From: "Dennis Huo (JIRA)" To: hdfs-issues@hadoop.apache.org Message-ID: In-Reply-To: References: Subject: [jira] [Updated] (HDFS-13056) Expose file-level composite CRCs in HDFS which are comparable across different instances/layouts MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-JIRA-FingerPrint: 30527f35849b9dde25b450d4833f0394 [ https://issues.apache.org/jira/browse/HDFS-13056?page=3Dcom.atlassia= n.jira.plugin.system.issuetabpanels:all-tabpanel ] Dennis Huo updated HDFS-13056: ------------------------------ Release Note:=20 =20 This feature adds a new `COMPOSITE_CRC` FileChecksum type which uses CRC co= mposition to remain completely chunk/block agnostic, and allows comparison = between striped vs replicated files, between different HDFS instances, and = possible even between HDFS and other external storage systems or local file= s. Without this option, HDFS FileChecksums are computed as "MD5 of MD5 of CRC"= across chunks and blocks, so that the checksums are dependent on the confi= gured chunk and block sizes, rather than only reflecting the logical file c= ontents. The feature works by changing the way individual chunk and block c= hecksums are combined at invocation time, so doesn't depend on or affect an= y persistent metadata; it can be used in-place in existing HDFS deployments= without any recomputation of block metadata. This option can be enabled or disabled at the granularity of individual cli= ent calls by setting the new configuration option `dfs.checksum.combine.mod= e` to `COMPOSITE_CRC`: hdfs dfs -Ddfs.checksum.combine.mode=3DCOMPOSITE_CRC -checksum hdfs:///= tmp/foo.txt By default, this configuration option is set to `MD5MD5CRC`, which preserve= s the fully backwards-compatible existing behavior of HDFS. Note that this "combine mode" is orthogonal to the existing `dfs.checksum.t= ype` configuration option, which configures the checksum algorithm at the l= evel of individual chunk crcs that are stored in block metadata, where `CRC= 32` specifies the legacy "gzip" CRC polynomial, and `CRC32C` specifies the = "Castagnoli" polynomial. The composite CRC mode will adhere to the checksum= type stored in the block metadata; if an HDFS instance stores a mixture of= files with `CRC32` and `CRC32C` types, the list of FileChecksums with `COM= POSITE_CRC` will likewise produce the corresponding mixture of `COMPOSITE-C= RC32` and `COMPOSITE-CRC32C` types. > Expose file-level composite CRCs in HDFS which are comparable across diff= erent instances/layouts > -------------------------------------------------------------------------= ----------------------- > > Key: HDFS-13056 > URL: https://issues.apache.org/jira/browse/HDFS-13056 > Project: Hadoop HDFS > Issue Type: New Feature > Components: datanode, distcp, erasure-coding, federation, hdfs > Affects Versions: 3.0.0 > Reporter: Dennis Huo > Assignee: Dennis Huo > Priority: Major > Fix For: 3.2.0, 3.1.1 > > Attachments: HDFS-13056-branch-2.8.001.patch, HDFS-13056-branch-2= .8.002.patch, HDFS-13056-branch-2.8.003.patch, HDFS-13056-branch-2.8.004.pa= tch, HDFS-13056-branch-2.8.005.patch, HDFS-13056-branch-2.8.poc1.patch, HDF= S-13056.001.patch, HDFS-13056.002.patch, HDFS-13056.003.patch, HDFS-13056.0= 03.patch, HDFS-13056.004.patch, HDFS-13056.005.patch, HDFS-13056.006.patch,= HDFS-13056.007.patch, HDFS-13056.008.patch, HDFS-13056.009.patch, HDFS-130= 56.010.patch, HDFS-13056.011.patch, HDFS-13056.012.patch, HDFS-13056.013.pa= tch, HDFS-13056.014.patch, Reference_only_zhen_PPOC_hadoop2.6.X.diff, hdfs-= file-composite-crc32-v1.pdf, hdfs-file-composite-crc32-v2.pdf, hdfs-file-co= mposite-crc32-v3.pdf > > > FileChecksum was first introduced in [https://issues-test.apache.org/jira= /browse/HADOOP-3981]=C2=A0and ever since then has remained defined as MD5-o= f-MD5-of-CRC, where per-512-byte chunk CRCs are already stored as part of d= atanode metadata, and the MD5 approach is used to=C2=A0compute an aggregate= value in a distributed manner, with individual datanodes computing the MD5= -of-CRCs per-block in parallel, and the HDFS client computing the second-le= vel MD5. > =C2=A0 > A shortcoming of this approach which is=C2=A0often brought up is the fact= that this FileChecksum is=C2=A0sensitive to the internal block-size and ch= unk-size configuration, and thus different HDFS=C2=A0files with different b= lock/chunk settings cannot be compared. More commonly, one might have diffe= rent HDFS clusters which use different block sizes, in which case any data = migration won't be able to use the FileChecksum for distcp's rsync function= ality or for verifying end-to-end data integrity (on top of low-level data = integrity checks applied at data transfer time). > =C2=A0 > This was also revisited in https://issues.apache.org/jira/browse/HDFS-843= 0=C2=A0during the addition of checksum support for striped erasure-coded fi= les; while there was some discussion of using CRC composability, it still u= ltimately settled on=C2=A0hierarchical MD5 approach, which=C2=A0also=C2=A0a= dds the problem that checksums of basic replicated files are not comparable= to striped files. > =C2=A0 > This feature proposes to add a "COMPOSITE-CRC" FileChecksum type which=C2= =A0uses CRC composition to remain completely chunk/block agnostic, and allo= ws comparison between striped vs replicated files, between different HDFS i= nstances, and possible even between HDFS and other=C2=A0external storage sy= stems. This feature can also be added in-place to be compatible with existi= ng block metadata, and doesn't need to change the normal path of chunk veri= fication, so is minimally invasive. This also means even large preexisting = HDFS deployments could adopt this feature to retroactively sync data. A det= ailed design document can be found here:=C2=A0https://storage.googleapis.co= m/dennishuo/hdfs-file-composite-crc32-v1.pdf -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: hdfs-issues-unsubscribe@hadoop.apache.org For additional commands, e-mail: hdfs-issues-help@hadoop.apache.org