[LUCENE-4123] Add CachingRAMDirectory

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: core/store
• Lucene Fields: New
• Assignee: Michael McCandless
• Reporter: Michael McCandless
• Created: 08/Jun/12 16:46
• Updated: 28/Aug/22 13:18

Description

The directory is very simple and useful if you have an index that you
know fully fits into available RAM. You could also use FileSwitchDir if
you want to leave some files (eg stored fields or term vectors) on disk.

It wraps any other Directory and delegates all writing (IndexOutput) to
it, but for reading (IndexInput), it allocates a single byte[] and fully
reads the file in and then serves requests off that single byte[]. It's
more GC friendly than RAMDir since it only allocates a single array per
file.

It has a few nocommits still, but all tests pass if I wrap the delegate
inside MockDirectoryWrapper using this.

I tested with 1M Wikipedia english index (would like to test w/ 10M docs
but I don't have enough RAM...); it seems to give a nice speedup:

                Task    QPS base StdDev base  QPS cachedStdDev cached      Pct diff
             Respell      197.00        7.27      203.19        8.17   -4% -   11%
            PKLookup      121.12        2.80      125.46        3.20   -1% -    8%
              Fuzzy2       66.62        2.62       69.91        2.85   -3% -   13%
              Fuzzy1      206.20        6.47      222.21        6.52    1% -   14%
       TermGroup100K      160.14        6.62      175.71        3.79    3% -   16%
              Phrase       34.85        0.40       38.75        0.61    8% -   14%
      TermBGroup100K      363.75       15.74      406.98       13.23    3% -   20%
            SpanNear       53.08        1.11       59.53        2.94    4% -   20%
    TermBGroup100K1P      222.53        9.78      252.86        5.96    6% -   21%
        SloppyPhrase       70.36        2.05       79.95        4.48    4% -   23%
            Wildcard      238.10        4.29      272.78        4.97   10% -   18%
           OrHighMed      123.49        4.85      149.32        4.66   12% -   29%
             Prefix3      288.46        8.10      350.40        5.38   16% -   26%
          OrHighHigh       76.46        3.27       93.13        2.96   13% -   31%
              IntNRQ       92.25        2.12      113.47        5.74   14% -   32%
                Term      757.12       39.03      958.62       22.68   17% -   36%
         AndHighHigh      103.03        4.48      133.89        3.76   21% -   39%
          AndHighMed      376.36       16.58      493.99       10.00   23% -   40%