# Calculating gcache.size value

**URL:** <https://forums.percona.com/t/calculating-gcache-size-value/30201>\
**Category:** Percona XtraDB Cluster 5.x\
**Created:** [May 10, 2024, 3:23am UTC](https://forums.percona.com/t/calculating-gcache-size-value/30201 "2024-05-10T03:23:10Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![brucehvn](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/brucehvn/32/13680_2.png) [@brucehvn](https://forums.percona.com/u/brucehvn)\
**Post date:** [May 10, 2024, 3:23am UTC](https://forums.percona.com/t/calculating-gcache-size-value/30201/1 "2024-05-10T03:23:10Z")

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Is there some formula for determining how large I should set the gcache.size value to? I have a db that looks like it is too large for the default 128M, so IST transfers won’t happen. The total size of the .ibd files in the datadir/dbfolder is about 11GB if that makes any difference.

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**Author:** ![matthewb](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/matthewb/32/34_2.png) [@matthewb](https://forums.percona.com/u/matthewb)\
**Post date:** [May 11, 2024, 5:59pm UTC](https://forums.percona.com/t/calculating-gcache-size-value/30201/4 "2024-05-11T17:59:17Z")

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@brucehvn There is no real guidance on gcache size. The idea is that you size the cache to the amount of data changes you do and how much time you’re willing to accept. For example, regardless of your dataset size, if you only change 5GB/hr, then a 5GB gcache will allow downtime of 1 member up to 1 hour before SST is required. If you change 2GB/hr, a 5GB gcache will allow 2.5hrs of downtime before SST. The choice/decision is up to you and your environment.

You must also ensure `gcache.recover=YES` is set in your config, otherwise IST will never happen.

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**Author:** ![CTutte](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/ctutte/32/1341_2.png) [@CTutte](https://forums.percona.com/u/CTutte)\
**Post date:** [May 13, 2024, 1:20pm UTC](https://forums.percona.com/t/calculating-gcache-size-value/30201/5 "2024-05-13T13:20:18Z")

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BTW; if you know that you will be doing some planned maintenance you can use “freeze\_purge\_at\_seqno” to avoid trashing the gcache until the down is back with IST

source: [Want IST Not SST for Node Rejoins? We Have a Solution!](https://www.percona.com/blog/no-sst-node-rejoins/)