3

According to the MongoDB documentation (at least this blog entry https://www.mongodb.com/blog/post/new-compression-options-mongodb-30), prefix compression is enabled by default on MongoDB.

However, when I look at one collection, I see this:

db.myCollection.stats()
{
...,
    "wiredTiger" : {
        "metadata" : {
            "formatVersion" : 1
        },
        "creationString" : "...,prefix_compression=0,prefix_compression_min=4"
...
}

Does prefix_compression=0 means that my indexes are not prefix-compressed ?

1
  • thank you for asking this question! I wondered the same
    – asgs
    Aug 10, 2022 at 14:36

1 Answer 1

3

By default collection stats only include information on the collection data (which uses block-level compression rather than prefix compression).

To see index details you need to provide an additional indexDetails option, eg:

db.myCollection.stats({indexDetails:true}).indexDetails._id_.creationString

You should see "prefix_compression=true" in the index creationString value.

1
  • thank you so much! I was confused like the OP was
    – asgs
    Aug 10, 2022 at 14:36

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