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Add CondensedStats monitoring utility, equivalent to vmstat
author Dominic Cleal <dominic-cleal@cdo2.com>
date Thu, 05 Aug 2010 11:07:25 +0100
parents 3dc0c5604566
children
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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1 <body>
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2
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Dan Creswell <dan.creswell@gmail.com>
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3 <P> The blitz storage engine lives in this package and is responsible for
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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4 storage and indexing of MangledEntry instances. It is built around the concept
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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5 of virtual memory with EntrySleeves being the equivalent of pages which can
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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6 be cached or written to Storage instances. </P>
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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8 <P> EntrySleeves contain a certain amount of transient information
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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9 (SleeveState) which is used to manage them whilst they are cached in
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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10 memory </P>
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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12 <P> EntrySleeves may be pinned in memory using the PINNED flag. This
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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13 prevents any state changes made from being reflected to disk (this is most
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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14 often used to prevent writes getting to disk until the containing
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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15 transaction has commited). Other flags identify dirty, deleted or never
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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parents:
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16 written EntrySleeves which determines what should be done when EntrySleeve
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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17 state is sync'd back to disk. </P>
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18
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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19 <P> Recently written entries are not immediately written to disk (though they
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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20 are logged) on the assumption that these Entries might well be immediately
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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21 taken which has the potential to save us a disk write/delete cycle. </P>
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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23 <P> Note: flushing in this context means removal from the cache and can only
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24 occur after sync'ing which is the copying of appropriate state to disk. Of
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25 course, if the state of an EntrySleeve hasn't changed disk needn't be updated.
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26 </P>
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27
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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28 <p> Storage management is mostly done in EntryStorage which delegates a lot
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29 of responsibility to WriteScheduler (manages PINNED Sleeves).
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30 WriteScheduler delegates handling of updates to WriteBuffer which
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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31 asynchronously updates disk via WriteDaemon. We use asynchronous writing
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32 because it allows the upper layers to avoid waiting for disks to perform an
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33 operation.</p>
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34
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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35 @see org.dancres.blitz.entry.SleeveState
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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36 @see org.dancres.blitz.entry.WriteScheduler
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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37 @see org.dancres.blitz.entry.WriteBuffer
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38 @see org.dancres.blitz.disk.WriteDaemon
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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39 </body>