Major Description
In log block container, blocks in .data file are append only, there is a related append only .metadata file to trace blocks in .data, this type of entries in metadata are in CREATE type, the other type of entries in metadata are type of DELETE, it means mark the corresponding CREATE block as deleted.
If there is a pair of CREATE and DELETE entries of a same block id, LBM use hole punch to reclaim disk space in .data file, but the entries in .metadata will not be compacted except bootstrap.
Another way to limit metadata is the .data file offset reach its size limitation(default 10GB), or block number in metadata reach its limitation(no limit on default).
I found a case in product environment that metadata consumed too many disk space and near to .data's disk space, it's a waste, and make users confused and complain that the actual disk space is far more than user's data.
[root@hybrid01 data]# du -cs *.metadata | sort -n | tail 19072 fb58e00979914e95aae7184e3189c8c6.metadata 19092 5bbf54294d5948c4a695e240e81d5f80.metadata 19168 89da5f3c4dfa469a9935f091bced1856.metadata 19200 f27e6ff14bd44fd1838f63f1be35ee64.metadata 19256 7b87a5e3c7fa4d3d86dcd3945d6741e1.metadata 19256 cf054d1aa7cb4f5cbbbce3b99189bbe1.metadata 19496 a6cbb4a284b842deafe6939be051c77c.metadata 19568 ba749640df684cb8868d6e51ea3d1b17.metadata 19924 e5469080934746e58b0fd2ba29d69c9d.metadata 148954280 total // all metadata size ~149GB [root@hybrid01 data]# du -cs *.data | sort -n | tail 64568 46dfbc5ac94d429b8d79a536727495df.data 64568 b4abc59d4eb2473ca267e0b057c8fad7.data 65728 576e09ed7e164ddebe5b1702be296619.data 66368 88d295f38dec4197bfbc6927e0528bde.data 90904 7291e10aafe74f2792168f6146738c5d.data 96788 6e72381ae95840f99864baacbc9169af.data 98060 c413553491764d039e702577606bac02.data 103556 a5db7a9c2e93457aa06103e45f59d8b4.data 138200 3876af02694643d49b19b39789460759.data 176443948 total // all data size ~176GB [root@hybrid01 data]# kudu pbc dump e5469080934746e58b0fd2ba29d69c9d.metadata --oneline | awk '{print $5}' | sort | uniq -c | egrep -v " 2 " 1 6165611810 // low live ratio, only 1 live block