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Accumulo by Billie Rinaldi, Aaron Cordova, Michael Wall

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Appendix B. Metadata Table

The metadata table contains a row for every tablet in Accumulo. Tablets are uniquely described by the ID of their table and the last row in the range assigned to the tablet, or end row. Table B-1 describes the columns that can appear in a tablet’s row in the metadata table, and Table B-2 shows some sample entries from a real metadata table.

In addition to tablet entries, there is a section of the metadata table that records file deletion entries. There is also a section for files that are in the process of being bulk-imported into Accumulo, to assist the garbage collector in not deleting these files prematurely. More about file deletion can be found in “Garbage Collector”.

Table B-1. Metadata table description
Row Column family Column qualifier Value

table id ; tablet end row

file

regular data file name

size in bytes , number of keys

table id ; tablet end row

future

tablet server session id

tserver IP : port

table id ; tablet end row

last

tablet server session id

tserver IP : port

table id ; tablet end row

loc

tablet server session id

tserver IP : port

table id ; tablet end row

log

server / log file name

log set | table id

table id ; tablet end row

scan

file currently being scanned

table id ; tablet end row

srv

compact

compaction id

table id ; tablet end row

srv

dir

tablet directory

table id ; tablet end row

srv

flush

flush id

table id ; tablet end row

srv

lock

zookeeper lock location

table id ; tablet end row

srv

time

M

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