Every S3 object has an associated Entity tag or ETag\nwhich can be used for file and object comparison. <\/p>\n\n\n\n
The ETag may or may not be an MD5 digest of the object\ndata. Basically, if the object was uploaded with a single PUT operation and\ndoesnt use Customer Managed or KMS keys for encryption then the resulting ETag\nis just the MD5 hexdigest of the object. If an object is created by either the\nMultipart Upload or Part Copy operation, the ETag is not an MD5 digest,\nregardless of the method of encryption.<\/p>\n\n\n\n
For multipart uploads the ETag is the MD5 hexdigest of\neach part\u2019s MD5 digest concatenated together, followed by the number of parts\nseparated by a dash.<\/p>\n\n\n\n
E.g. for a two part object the ETag may look something\nlike this: d41d8cd98f00b204e9800998ecf8427e-2<\/p>\n\n\n\n
Which can be represented by: hexmd5(md5(part1) +\nmd5(part2))-2<\/p>\n\n\n\n
Many S3 clients store a pre-calculated MD5 checksum of\nthe object for use in comparison and sync operations. This is time consuming\nand essentially obsolete as the existing ETag can be used for comparison\nresulting in quicker uploads\/sync operations.<\/p>\n\n\n\n
Clients should instead implement a method to compute an\nETag for local file comparison.<\/p>\n","protected":false},"excerpt":{"rendered":"
AWS S3 ETag Every S3 object has an associated Entity tag or ETag which can be used for file and object comparison. The ETag may or may not be an MD5 digest of the object data. Basically, if the object was uploaded with a single PUT operation and doesnt use Customer Managed or KMS keys…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"categories":[2],"tags":[],"class_list":["post-1082","page","type-page","status-publish","hentry","category-amazon-aws"],"acf":[],"yoast_head":"\n