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https://issues.apache.org/jira/browse/CASSANDRA-3143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13169900#comment-13169900
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Sylvain Lebresne commented on CASSANDRA-3143:
---------------------------------------------
bq. On the other hand, if we will be using descriptor -> id relationship,
wouldn't it create the same amount of additional I/O (+ expenses on such cache
maintain) as just having Descriptor as cache key?
I'm not talking of changing KeyCacheKey in any way. I'm talking of making the
key cache save being 2 files (keySave and keySaveMetadata) having the key cache
save method looking something like that (in pseudo-code):
{noformat}
Map<Descriptor, Integer> assoc = new HashMap();
int nextId = 0;
for (KeyCacheKey key : keys)
{
Integer id = assoc.get(key.desc);
if (id == null)
{
// descriptor we haven't seen yet during this save
id = nextId++;
assoc.put(key.desc, id);
keySaveMetadata.write(key.desc => id)
}
keySave.write(id => key.key)
}
{noformat}
And the reading would first load the map from keySaveMetadata and read keySave.
bq. Sure, I will just change that to 40 bytes and update doc for
key_cache_size_in_mb
I would be in favor of not documenting this in the yaml as it'll confuse more
user than anything else and we don't want anyone to rely on that formula.
> Global caches (key/row)
> -----------------------
>
> Key: CASSANDRA-3143
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3143
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Pavel Yaskevich
> Assignee: Pavel Yaskevich
> Priority: Minor
> Labels: Core
> Fix For: 1.1
>
> Attachments: 0001-global-key-cache.patch,
> 0002-global-row-cache-and-ASC.readSaved-changed-to-abstra.patch,
> 0003-CacheServiceMBean-and-correct-key-cache-loading.patch,
> 0004-key-row-cache-tests-and-tweaks.patch,
> 0005-cleanup-of-the-CFMetaData-and-thrift-avro-CfDef-and-.patch,
> 0006-row-key-cache-improvements-according-to-Sylvain-s-co.patch
>
>
> Caches are difficult to configure well as ColumnFamilies are added, similar
> to how memtables were difficult pre-CASSANDRA-2006.
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