hbase之宽表与窄表对split的影响

     hbase的hbase.hregion.max.filesize属性值用来指定region分割的阀值， 该值默认为268435456(256MB), 当一个列族文件大小超过该值时，将会分裂成两个region。
     hbase的列可以有很多，设计时有两种方式可选择， 宽表（一行有很多列）和窄表
如有一个存储用户邮件的表
按宽表设计时，可以表示成（一个用户的所有邮件存成一行)
userid1 email1 emali2 email3 ... ... ... ... ... emailn
userid2 email1 emali2 email3 ... ... ... ... ... emailn
useridn                 
按窄表设计时，可以表示成(rowkey由用ID和emailID组成)
userid1_emialid1  email1
userid1_emialid2  email2
userid1_emialid3  email2
userid1_emialidn  emailn
userid2_emialid1  email1
userid2_emialid2  email2
userid2_emialid3  email3
userid2_emialidn  emailn
这两种设计方法会对region的分割造成影响， 今天在看HFileOutputFormat代码时发现它new出的RecordWriter对 region分割有一定的限制，

只有当rowkey不同是才会做分割, 而rowkey相同时即使region大小已经超过hbase.hregion.max.filesize值， 也不会分割
RecordWriter代码:

public void write(ImmutableBytesWritable row, KeyValue kv)
      throws IOException {
        long length = kv.getLength();
        byte [] family = kv.getFamily();
        WriterLength wl = this.writers.get(family);
        if (wl == null || ((length + wl.written) >= maxsize) &&
            Bytes.compareTo(this.previousRow, 0, this.previousRow.length,
              kv.getBuffer(), kv.getRowOffset(), kv.getRowLength()) != 0) {
          // Get a new writer.
          Path basedir = new Path(outputdir, Bytes.toString(family));
          if (wl == null) {
            wl = new WriterLength();
            this.writers.put(family, wl);
            if (this.writers.size() > 1) throw new IOException("One family only");
            // If wl == null, first file in family.  Ensure family dir exits.
            if (!fs.exists(basedir)) fs.mkdirs(basedir);
          }
          wl.writer = getNewWriter(wl.writer, basedir);
          LOG.info("Writer=" + wl.writer.getPath() +
            ((wl.written == 0)? "": ", wrote=" + wl.written));
          wl.written = 0;
        }
        kv.updateLatestStamp(this.now);
        wl.writer.append(kv);
        wl.written += length;
        // Copy the row so we know when a row transition.
        this.previousRow = kv.getRow();
      }

标红加粗部分说明当块大小大于hbase.hregion.max.filesize值， 并却当前行与上一次插入的行不同时才会分割region.
1. 宽表情况下， 单独一行大小超过hbase.hregion.max.filesize值， 不会做分割
2. 相同rowkey下插入很多不同版本的记录，即使大小超过hbase.hregion.max.filesize值， 也不会做分割

下面就来验证下：
为了尽早看到效果， 需要在hbase-site.xml中修改两个配置参数

<property>
    <name>hbase.hregion.memstore.flush.size</name>
    <value>5</value>
    <description>
    Memstore will be flushed to disk if size of the memstore
    exceeds this number of bytes.  Value is checked by a thread that runs
    every hbase.server.thread.wakefrequency.
    </description>
  </property>
<property>
    <name>hbase.hregion.max.filesize</name>
    <value>10</value>
    <description>
    Maximum HStoreFile size. If any one of a column families' HStoreFiles has
    grown to exceed this value, the hosting HRegion is split in two.
    Default: 256M.
    </description>
  </property>

 建测试表t1和t2

hbase(main):076:0* create 't1','f1'
0 row(s) in 1.6460 seconds

hbase(main):077:0> create 't2','f1'
0 row(s) in 1.1790 seconds

查看系统表 .META.

hbase(main):081:0* scan '.META.'
ROW                                                 COLUMN+CELL
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:regioninfo, timestamp=1314720667384, value=REGION => {NAME => 't1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => d8acd6bc659ac8326b88850d645a90ad, TABLE => {{NAME => 't1', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', COMPRESSION => 'NONE', VERSIONS => '3', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:server, timestamp=1314720667941, value=yinjie:60020
 .
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:serverstartcode, timestamp=1314720667941, value=1314716290123
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:regioninfo, timestamp=1314720672241, value=REGION => {NAME => 't2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => 16bb3d2563eab3b4e25477c64e007e71, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', COMPRESSION => 'NONE', VERSIONS => '3', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:server, timestamp=1314720672346, value=yinjie:60020
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:serverstartcode, timestamp=1314720672346, value=1314716290123
 .
2 row(s) in 0.0230 seconds

可以看到此时，t1,t2都已有一个region
先往t1表插入10条记录，rowkwy相同

hbase(main):086:0* for i in 0..9 do\
hbase(main):087:1* put 't1','row1',"f1:c#{i}","swallow#{i}"\
hbase(main):088:1* end
0 row(s) in 0.0180 seconds

0 row(s) in 0.0070 seconds

0 row(s) in 0.0420 seconds

0 row(s) in 0.0620 seconds

0 row(s) in 0.0120 seconds

0 row(s) in 0.0770 seconds

0 row(s) in 0.0150 seconds

0 row(s) in 0.1290 seconds

0 row(s) in 10.0740 seconds

0 row(s) in 0.1230 seconds

=> 0..9
hbase(main):089:0>

查看t1记录

hbase(main):089:0> scan 't1'
ROW                                                 COLUMN+CELL
 row1                                               column=f1:c0, timestamp=1314720946495, value=swallow0
 row1                                               column=f1:c1, timestamp=1314720946507, value=swallow1
 row1                                               column=f1:c2, timestamp=1314720946903, value=swallow2
 row1                                               column=f1:c3, timestamp=1314720946939, value=swallow3
 row1                                               column=f1:c4, timestamp=1314720946976, value=swallow4
 row1                                               column=f1:c5, timestamp=1314720947055, value=swallow5
 row1                                               column=f1:c6, timestamp=1314720947070, value=swallow6
 row1                                               column=f1:c7, timestamp=1314720947198, value=swallow7
 row1                                               column=f1:c8, timestamp=1314720957272, value=swallow8
 row1                                               column=f1:c9, timestamp=1314720957392, value=swallow9
1 row(s) in 0.0300 seconds

查看 .META.

hbase(main):090:0> scan '.META.'
ROW                                                 COLUMN+CELL
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:regioninfo, timestamp=1314720667384, value=REGION => {NAME => 't1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => d8acd6bc659ac8326b88850d645a90ad, TABLE => {{NAME => 't1', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', COMPRESSION => 'NONE', VERSIONS => '3', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:server, timestamp=1314720667941, value=yinjie:60020
 .
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:serverstartcode, timestamp=1314720667941, value=1314716290123
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:regioninfo, timestamp=1314720672241, value=REGION => {NAME => 't2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => 16bb3d2563eab3b4e25477c64e007e71, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', COMPRESSION => 'NONE', VERSIONS => '3', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:server, timestamp=1314720672346, value=yinjie:60020
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:serverstartcode, timestamp=1314720672346, value=1314716290123
 .
2 row(s) in 0.0210 seconds

可以看到t1仍旧只有一个region

接下去往往t2表插入10条相同记录，但rowkwy不同

hbase(main):091:0> for i in 0..9 do\
hbase(main):092:1* put 't2',"row#{i}","f1:c#{i}","swallow#{i}"\
hbase(main):093:1* end
0 row(s) in 0.1140 seconds

0 row(s) in 0.0080 seconds

0 row(s) in 0.0410 seconds

0 row(s) in 0.0820 seconds

0 row(s) in 0.0210 seconds

0 row(s) in 0.0410 seconds

0 row(s) in 0.0200 seconds

0 row(s) in 0.1210 seconds

0 row(s) in 0.0140 seconds

0 row(s) in 0.0360 seconds

=> 0..9

查看t2记录

hbase(main):097:0* scan 't2'
ROW                                                 COLUMN+CELL
 row0                                               column=f1:c0, timestamp=1314721110769, value=swallow0
 row1                                               column=f1:c1, timestamp=1314721110787, value=swallow1
 row2                                               column=f1:c2, timestamp=1314721110830, value=swallow2
 row3                                               column=f1:c3, timestamp=1314721110916, value=swallow3
 row4                                               column=f1:c4, timestamp=1314721110932, value=swallow4
 row5                                               column=f1:c5, timestamp=1314721110971, value=swallow5
 row6                                               column=f1:c6, timestamp=1314721110989, value=swallow6
 row7                                               column=f1:c7, timestamp=1314721111121, value=swallow7
 row8                                               column=f1:c8, timestamp=1314721111130, value=swallow8
 row9                                               column=f1:c9, timestamp=1314721111172, value=swallow9
10 row(s) in 1.0450 seconds

查看 .META.

hbase(main):102:0> scan '.META.'
ROW                                                 COLUMN+CELL
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:regioninfo, timestamp=1314720667384, value=REGION => {NAME => 't1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => d8acd6bc659ac8326b88850d645a90ad, TABLE => {{NAME => 't1', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', COMPRESSION => 'NONE', VERSIONS => '3', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:server, timestamp=1314720667941, value=yinjie:60020
 .
 t1,,1314720667274.d8acd6bc659ac8326b88850d645a90ad column=info:serverstartcode, timestamp=1314720667941, value=1314716290123
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:regioninfo, timestamp=1314721112130, value=REGION => {NAME => 't2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71.', STARTKEY => '', ENDK
 .                                                  EY => '', ENCODED => 16bb3d2563eab3b4e25477c64e007e71, OFFLINE => true, SPLIT => true, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILT
                                                    ER => 'NONE', REPLICATION_SCOPE => '0', VERSIONS => '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOC
                                                    KCACHE => 'true'}]}}
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:server, timestamp=1314720672346, value=yinjie:60020
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:serverstartcode, timestamp=1314720672346, value=1314716290123
 .
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:splitA, timestamp=1314721112130, value=REGION => {NAME => 't2,,1314721111490.71df02214242923574b71fe5e2a19360.', STARTKEY => '', ENDKEY =
 .                                                  > 'row0', ENCODED => 71df02214242923574b71fe5e2a19360, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SCOPE
                                                    => '0', VERSIONS => '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,,1314720672168.16bb3d2563eab3b4e25477c64e007e71 column=info:splitB, timestamp=1314721112130, value=REGION => {NAME => 't2,row0,1314721111490.915ee8d4a32c59a4ec3960e335b061ca.', STARTKEY => 'row0',
 .                                                  ENDKEY => '', ENCODED => 915ee8d4a32c59a4ec3960e335b061ca, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SC
                                                    OPE => '0', VERSIONS => '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,,1314721111490.71df02214242923574b71fe5e2a19360 column=info:regioninfo, timestamp=1314721112267, value=REGION => {NAME => 't2,,1314721111490.71df02214242923574b71fe5e2a19360.', STARTKEY => '', ENDK
 .                                                  EY => 'row0', ENCODED => 71df02214242923574b71fe5e2a19360, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATION_SC
                                                    OPE => '0', VERSIONS => '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,,1314721111490.71df02214242923574b71fe5e2a19360 column=info:server, timestamp=1314721112267, value=yinjie:60020
 .
 t2,,1314721111490.71df02214242923574b71fe5e2a19360 column=info:serverstartcode, timestamp=1314721112267, value=1314716290123
 .
 t2,row0,1314721111490.915ee8d4a32c59a4ec3960e335b0 column=info:regioninfo, timestamp=1314721112627, value=REGION => {NAME => 't2,row0,1314721111490.915ee8d4a32c59a4ec3960e335b061ca.', STARTKEY => 'row
 61ca.                                              0', ENDKEY => '', ENCODED => 915ee8d4a32c59a4ec3960e335b061ca, TABLE => {{NAME => 't2', FAMILIES => [{NAME => 'f1', BLOOMFILTER => 'NONE', REPLICATIO
                                                    N_SCOPE => '0', VERSIONS => '3', COMPRESSION => 'NONE', TTL => '2147483647', BLOCKSIZE => '65536', IN_MEMORY => 'false', BLOCKCACHE => 'true'}]}}
 t2,row0,1314721111490.915ee8d4a32c59a4ec3960e335b0 column=info:server, timestamp=1314721112627, value=yinjie:60020
 61ca.
 t2,row0,1314721111490.915ee8d4a32c59a4ec3960e335b0 column=info:serverstartcode, timestamp=1314721112627, value=1314716290123
 61ca.
4 row(s) in 0.0380 seconds

可以看到t2的region已经分裂.