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Hi, We recently upgraded out MongoDB from community version 3.4.14 to 4.0.1 We see that the compression ratio differs for the same type of data between the version Hence we did a test and found that compression ratio drastically fell for 3.6+ Version Raw size Storage size Comp Ratio 4.0 10378066324 1594658816 6.5x 3.6 10378066324 1599205376 6.49x 3.4 10378066324 634499072 16.35x Can you please suggest if any changes has to be made in the configuration of MongoDB or WiredTiger? Below is the wired tiger configuration we are using wiredTiger: collectionConfig: blockCompressor: zlib engineConfig: directoryForIndexes: true journalCompressor: none cacheSizeGB: 40 configString: "eviction_dirty_target=60, eviction_dirty_trigger=80, eviction=(threads_min=20,threads_max=20)" Thanks, Tanveer

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tanveerm@xilinx.com commented on Thu, 23 Aug 2018 15:59:03 +0000: Thanks Eric !!! milkie commented on Thu, 23 Aug 2018 15:52:43 +0000: Version 4.0.2 is still unreleased, but it will be released in the coming months; watch for an announcement on the mongodb-announce google group. The fix is also proposed for backport into the 3.6 branch. tanveerm@xilinx.com commented on Thu, 23 Aug 2018 15:41:31 +0000: Hi Eric, Thanks for sharing the information !!!! I see that currently 4.0.1 is marked as the Current Stable Release on https://www.mongodb.com/download-center#community Can you share the link with me where to get 4.0.2 binaries? Thanks, Tanveer milkie commented on Thu, 23 Aug 2018 12:31:08 +0000: Thank you for your report. I believe we have fixed the compression ratio issue you are experiencing. Please see the linked tickets for more info; in particular, in WT-3968 we improved compression for zlib in version 4.0.2.

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