Re: how client location a region/tablet?
For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client¹s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
Re: how client location a region/tablet?
Doug, very informative document. Thanks a lot! I read through it and have some thoughts, - Supposing at the beginning, client side cache for region information is empty, and the client wants to GET row-key 123 from table ABC; - The client will read from ROOT table at first. But unfortunately, ROOT table only contains region information for META table (please correct me if I am wrong), but not region information for real data table (e.g. table ABC); - Does the client have to call each META region server one by one, in order to find which META region contains information for region owner of row-key 123 of data table ABC? BTW: I think if there is a way to expose information about what range of table/region each META region contains from .META. region key, it will be better to save time to iterate META region server one by one. Please feel free to correct me if I am wrong. regards, Lin On Thu, Aug 23, 2012 at 8:21 PM, Doug Meil doug.m...@explorysmedical.comwrote: For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client¹s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
Re: how client location a region/tablet?
Dong, Some more thoughts, after reading data structure for HRegionInfo = http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HRegionInfo.html, start key and end key looks informative which we could leverage, - I am not sure if we could leverage this information (stored as part of value in table ROOT) to find which META region may contains region server information for row-key 123 of data table ABC; - But I think unfortunately the information is stored in value of table ROOT, other than key field of table ROOT, so that we have to iterate each row in ROOT table one by one to figure out which META region server to access. Not sure if I get the points. Please feel free to correct me. regards, Lin On Thu, Aug 23, 2012 at 11:15 PM, Lin Ma lin...@gmail.com wrote: Doug, very informative document. Thanks a lot! I read through it and have some thoughts, - Supposing at the beginning, client side cache for region information is empty, and the client wants to GET row-key 123 from table ABC; - The client will read from ROOT table at first. But unfortunately, ROOT table only contains region information for META table (please correct me if I am wrong), but not region information for real data table (e.g. table ABC); - Does the client have to call each META region server one by one, in order to find which META region contains information for region owner of row-key 123 of data table ABC? BTW: I think if there is a way to expose information about what range of table/region each META region contains from .META. region key, it will be better to save time to iterate META region server one by one. Please feel free to correct me if I am wrong. regards, Lin On Thu, Aug 23, 2012 at 8:21 PM, Doug Meil doug.m...@explorysmedical.comwrote: For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client¹s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
Re: how client location a region/tablet?
HBase currently keeps a single META region (Doesn't split it). ROOT holds META region location, and META has a few rows in it, a few of them for each table. See also the class MetaScanner. On Thu, Aug 23, 2012 at 9:00 PM, Lin Ma lin...@gmail.com wrote: Dong, Some more thoughts, after reading data structure for HRegionInfo = http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HRegionInfo.html, start key and end key looks informative which we could leverage, - I am not sure if we could leverage this information (stored as part of value in table ROOT) to find which META region may contains region server information for row-key 123 of data table ABC; - But I think unfortunately the information is stored in value of table ROOT, other than key field of table ROOT, so that we have to iterate each row in ROOT table one by one to figure out which META region server to access. Not sure if I get the points. Please feel free to correct me. regards, Lin On Thu, Aug 23, 2012 at 11:15 PM, Lin Ma lin...@gmail.com wrote: Doug, very informative document. Thanks a lot! I read through it and have some thoughts, - Supposing at the beginning, client side cache for region information is empty, and the client wants to GET row-key 123 from table ABC; - The client will read from ROOT table at first. But unfortunately, ROOT table only contains region information for META table (please correct me if I am wrong), but not region information for real data table (e.g. table ABC); - Does the client have to call each META region server one by one, in order to find which META region contains information for region owner of row-key 123 of data table ABC? BTW: I think if there is a way to expose information about what range of table/region each META region contains from .META. region key, it will be better to save time to iterate META region server one by one. Please feel free to correct me if I am wrong. regards, Lin On Thu, Aug 23, 2012 at 8:21 PM, Doug Meil doug.m...@explorysmedical.comwrote: For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client¹s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack -- Harsh J
Re: how client location a region/tablet?
Lin, On Thu, Aug 23, 2012 at 10:10 PM, Lin Ma lin...@gmail.com wrote: Thanks, Harsh! - HBase currently keeps a single META region (Doesn't split it). -- does it mean there is only one row in ROOT table, which points the only one META region? Yes, currently this is the case. We disabled multiple META regions at some point, I am unsure about why exactly but perhaps it was complex to maintain that. - In Big Table, it seems they have multiple META regions (tablets), is it an advantage over HBase? :-) Well, depends. A single META region hasn't proven as a scalability bottleneck to anyone yet. A single META region can easily serve millions of rows if needed, like any other region, and I've usually not seen META table grow so big in deployments. -- Harsh J
RE: how client location a region/tablet?
I too thought there are multiple meta regions where as just one ROOT. May be I am mixing b/w Big Table and Hbase. Thanks, Abhishek -Original Message- From: Lin Ma [mailto:lin...@gmail.com] Sent: Thursday, August 23, 2012 9:41 AM To: user@hbase.apache.org; ha...@cloudera.com Cc: doug.m...@explorysmedical.com Subject: Re: how client location a region/tablet? Thanks, Harsh! - HBase currently keeps a single META region (Doesn't split it). -- does it mean there is only one row in ROOT table, which points the only one META region? - In Big Table, it seems they have multiple META regions (tablets), is it an advantage over HBase? :-) regards, Lin On Thu, Aug 23, 2012 at 11:48 PM, Harsh J ha...@cloudera.com wrote: HBase currently keeps a single META region (Doesn't split it). ROOT holds META region location, and META has a few rows in it, a few of them for each table. See also the class MetaScanner. On Thu, Aug 23, 2012 at 9:00 PM, Lin Ma lin...@gmail.com wrote: Dong, Some more thoughts, after reading data structure for HRegionInfo = http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HRegionInfo. html , start key and end key looks informative which we could leverage, - I am not sure if we could leverage this information (stored as part of value in table ROOT) to find which META region may contains region server information for row-key 123 of data table ABC; - But I think unfortunately the information is stored in value of table ROOT, other than key field of table ROOT, so that we have to iterate each row in ROOT table one by one to figure out which META region server to access. Not sure if I get the points. Please feel free to correct me. regards, Lin On Thu, Aug 23, 2012 at 11:15 PM, Lin Ma lin...@gmail.com wrote: Doug, very informative document. Thanks a lot! I read through it and have some thoughts, - Supposing at the beginning, client side cache for region information is empty, and the client wants to GET row-key 123 from table ABC; - The client will read from ROOT table at first. But unfortunately, ROOT table only contains region information for META table (please correct me if I am wrong), but not region information for real data table (e.g. table ABC); - Does the client have to call each META region server one by one, in order to find which META region contains information for region owner of row-key 123 of data table ABC? BTW: I think if there is a way to expose information about what range of table/region each META region contains from .META. region key, it will be better to save time to iterate META region server one by one. Please feel free to correct me if I am wrong. regards, Lin On Thu, Aug 23, 2012 at 8:21 PM, Doug Meil doug.m...@explorysmedical.comwrote: For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client¹s cache is stale, the location
Re: how client location a region/tablet?
Thank you Harsh. You answered my question. I like the current architecture of HBase, which is designed for extensibility for the future -- we have two layer index of data structure, and we can utilize it when needed for specific problems. It looks like you buy a 4 bed-room house, but only utilizing one room for living before having more children. :-) regards, Lin On Fri, Aug 24, 2012 at 12:46 AM, Harsh J ha...@cloudera.com wrote: Lin, On Thu, Aug 23, 2012 at 10:10 PM, Lin Ma lin...@gmail.com wrote: Thanks, Harsh! - HBase currently keeps a single META region (Doesn't split it). -- does it mean there is only one row in ROOT table, which points the only one META region? Yes, currently this is the case. We disabled multiple META regions at some point, I am unsure about why exactly but perhaps it was complex to maintain that. - In Big Table, it seems they have multiple META regions (tablets), is it an advantage over HBase? :-) Well, depends. A single META region hasn't proven as a scalability bottleneck to anyone yet. A single META region can easily serve millions of rows if needed, like any other region, and I've usually not seen META table grow so big in deployments. -- Harsh J
Re: how client location a region/tablet?
Me too, Abhishek -- you are not alone. But it is good to learn and discuss here to know various design choices. regards, Lin On Fri, Aug 24, 2012 at 1:06 AM, Pamecha, Abhishek apame...@x.com wrote: I too thought there are multiple meta regions where as just one ROOT. May be I am mixing b/w Big Table and Hbase. Thanks, Abhishek -Original Message- From: Lin Ma [mailto:lin...@gmail.com] Sent: Thursday, August 23, 2012 9:41 AM To: user@hbase.apache.org; ha...@cloudera.com Cc: doug.m...@explorysmedical.com Subject: Re: how client location a region/tablet? Thanks, Harsh! - HBase currently keeps a single META region (Doesn't split it). -- does it mean there is only one row in ROOT table, which points the only one META region? - In Big Table, it seems they have multiple META regions (tablets), is it an advantage over HBase? :-) regards, Lin On Thu, Aug 23, 2012 at 11:48 PM, Harsh J ha...@cloudera.com wrote: HBase currently keeps a single META region (Doesn't split it). ROOT holds META region location, and META has a few rows in it, a few of them for each table. See also the class MetaScanner. On Thu, Aug 23, 2012 at 9:00 PM, Lin Ma lin...@gmail.com wrote: Dong, Some more thoughts, after reading data structure for HRegionInfo = http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HRegionInfo. html , start key and end key looks informative which we could leverage, - I am not sure if we could leverage this information (stored as part of value in table ROOT) to find which META region may contains region server information for row-key 123 of data table ABC; - But I think unfortunately the information is stored in value of table ROOT, other than key field of table ROOT, so that we have to iterate each row in ROOT table one by one to figure out which META region server to access. Not sure if I get the points. Please feel free to correct me. regards, Lin On Thu, Aug 23, 2012 at 11:15 PM, Lin Ma lin...@gmail.com wrote: Doug, very informative document. Thanks a lot! I read through it and have some thoughts, - Supposing at the beginning, client side cache for region information is empty, and the client wants to GET row-key 123 from table ABC; - The client will read from ROOT table at first. But unfortunately, ROOT table only contains region information for META table (please correct me if I am wrong), but not region information for real data table (e.g. table ABC); - Does the client have to call each META region server one by one, in order to find which META region contains information for region owner of row-key 123 of data table ABC? BTW: I think if there is a way to expose information about what range of table/region each META region contains from .META. region key, it will be better to save time to iterate META region server one by one. Please feel free to correct me if I am wrong. regards, Lin On Thu, Aug 23, 2012 at 8:21 PM, Doug Meil doug.m...@explorysmedical.comwrote: For further information about the catalog tables and region-regionserver assignment, see thisŠ http://hbase.apache.org/book.html#arch.catalog On 8/19/12 7:36 AM, Lin Ma lin...@gmail.com wrote: Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA
Re: how client location a region/tablet?
That is spot on Stack, it is the worst case scenario as you describe, i.e. all cached information is stale. Lars On Aug 19, 2012, at 6:40 AM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client’s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
Re: how client location a region/tablet?
Thank you Stack, especially for the smart 6 round trip guess for the puzzle. :-) 1. Yeah, we client cache's locations, not the data. -- does it mean for each client, it will cache all location information of a HBase cluster, i.e. which physical server owns which region? Supposing each region has 128M bytes, for a big cluster (P-bytes level), total data size / 128M is not a trivial number, not sure if any overhead to client? 2. A bit confused by what do you mean not the data? For the client cached location information, it should be the data in table METADATA, which is region / physical server mapping data. Why you say not data (do you mean real content in each region)? regards, Lin On Sun, Aug 19, 2012 at 12:40 PM, Stack st...@duboce.net wrote: On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client’s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
how client location a region/tablet?
Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client’s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) have a good weekend, Lin
Re: how client location a region/tablet?
On Sat, Aug 18, 2012 at 2:13 AM, Lin Ma lin...@gmail.com wrote: Hello guys, I am referencing the Big Table paper about how a client locates a tablet. In section 5.1 Tablet location, it is mentioned that client will cache all tablet locations, I think it means client will cache root tablet in METADATA table, and all other tablets in METADATA table (which means client cache the whole METADATA table?). My question is, whether HBase implements in the same or similar way? My concern or confusion is, supposing each tablet or region file is 128M bytes, it will be very huge space (i.e. memory footprint) for each client to cache all tablets or region files of METADATA table. Is it doable or feasible in real HBase clusters? Thanks. Yeah, we client cache's locations, not the data. BTW: another confusion from me is in the paper of Big Table section 5.1 Tablet location, it is mentioned that If the client’s cache is stale, the location algorithm could take up to six round-trips, because stale cache entries are only discovered upon misses (assuming that METADATA tablets do not move very frequently)., I do not know how the 6 times round trip time is calculated, if anyone could answer this puzzle, it will be great. :-) I'm not sure what the 6 is about either. Here is a guesstimate: 1. Go to cached location for a server for a particular user region, but server says that it does not have a region, the client location is stale 2. Go back to client cached meta region that holds user region w/ row we want, but its location is stale. 3. Go to root location, to find new location of meta, but the root location has moved what the client has is stale 4. Find new root location and do lookup of meta region location 5. Go to meta region location to find new user region 6. Go to server w/ user region St.Ack
